Merge branch 'dev' into dankrad-patch-3

# Conflicts: # specs/simple-serialize.md
2019-05-07 18:10:18 +01:00 · 2019-05-07 18:10:18 +01:00 · b3501fbf2b
parent b1930d2239 f0fcbfd8fc
commit b3501fbf2b
51 changed files with 1146 additions and 820 deletions
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@ -60,15 +60,15 @@ jobs:
      - restore_cache:
          key: v1-specs-repo-{{ .Branch }}-{{ .Revision }}
      - restore_cached_venv:
-          venv_name: v1-test_libs
-          reqs_checksum: '{{ checksum "test_libs/pyspec/setup.py" }}'
+          venv_name: v1-pyspec
+          reqs_checksum: '{{ checksum "test_libs/pyspec/requirements.txt" }}-{{ checksum "test_libs/pyspec/requirements-testing.txt" }}'
      - run:
          name: Install pyspec requirements
          command: make install_test
      - save_cached_venv:
-          venv_name: v1-test_libs
-          reqs_checksum: '{{ checksum "test_libs/pyspec/setup.py" }}'
-          venv_path: ./test_libs/venv
+          venv_name: v1-pyspec
+          reqs_checksum: '{{ checksum "test_libs/pyspec/requirements.txt" }}-{{ checksum "test_libs/pyspec/requirements-testing.txt" }}'
+          venv_path: ./test_libs/pyspec/venv
  test:
    docker:
      - image: circleci/python:3.6
@ -77,8 +77,8 @@ jobs:
      - restore_cache:
          key: v1-specs-repo-{{ .Branch }}-{{ .Revision }}
      - restore_cached_venv:
-          venv_name: v1-test_libs
-          reqs_checksum: '{{ checksum "test_libs/pyspec/setup.py" }}'
+          venv_name: v1-pyspec
+          reqs_checksum: '{{ checksum "test_libs/pyspec/requirements.txt" }}-{{ checksum "test_libs/pyspec/requirements-testing.txt" }}'
      - run:
          name: Run py-tests
          command: make citest
--- a/.gitignore
+++ b/.gitignore
@ -4,10 +4,6 @@ venv
 .venvs
 .venv
 /.pytest_cache
-*.egg
-*.egg-info
-eggs
-.eggs

 build/
 output/
@ -17,6 +13,3 @@ eth2.0-spec-tests/

 # Dynamically built from Markdown spec
 test_libs/pyspec/eth2spec/phase0/spec.py
-
-# vscode
-.vscode/**
--- a/14
+++ b/14
@ -2,7 +2,6 @@ SPEC_DIR = ./specs
 SCRIPT_DIR = ./scripts
 TEST_LIBS_DIR = ./test_libs
 PY_SPEC_DIR = $(TEST_LIBS_DIR)/pyspec
-CONFIG_HELPERS_DIR = $(TEST_LIBS_DIR)/config_helpers
 YAML_TEST_DIR = ./eth2.0-spec-tests/tests
 GENERATOR_DIR = ./test_generators
 CONFIGS_DIR = ./configs
@ -24,8 +23,7 @@ all: $(PY_SPEC_ALL_TARGETS) $(YAML_TEST_DIR) $(YAML_TEST_TARGETS)
 clean:
 	rm -rf $(YAML_TEST_DIR)
 	rm -rf $(GENERATOR_VENVS)
-	rm -rf $(TEST_LIBS_DIR)/venv
-	rm -rf $(PY_SPEC_DIR)/.pytest_cache
+	rm -rf $(PY_SPEC_DIR)/venv $(PY_SPEC_DIR)/.pytest_cache
 	rm -rf $(PY_SPEC_ALL_TARGETS)

 # "make gen_yaml_tests" to run generators
@ -33,17 +31,13 @@ gen_yaml_tests: $(PY_SPEC_ALL_TARGETS) $(YAML_TEST_TARGETS)

 # installs the packages to run pyspec tests
 install_test:
-	cd $(TEST_LIBS_DIR); python3 -m venv venv; . venv/bin/activate; \
-	cd ..; cd $(CONFIG_HELPERS_DIR); pip3 install -e .; \
-	cd ../..; cd $(PY_SPEC_DIR); pip3 install -e .[dev];
+	cd $(PY_SPEC_DIR); python3 -m venv venv; . venv/bin/activate; pip3 install -r requirements-testing.txt;

 test: $(PY_SPEC_ALL_TARGETS)
-	cd $(TEST_LIBS_DIR); . venv/bin/activate; \
-	cd ..; cd $(PY_SPEC_DIR); python -m pytest .;
+	cd $(PY_SPEC_DIR); . venv/bin/activate; python -m pytest .

 citest: $(PY_SPEC_ALL_TARGETS)
-	cd $(TEST_LIBS_DIR); . venv/bin/activate; \
-	cd ..; cd $(PY_SPEC_DIR); mkdir -p test-reports/eth2spec; python -m pytest --junitxml=test-reports/eth2spec/test_results.xml .
+	cd $(PY_SPEC_DIR); mkdir -p test-reports/eth2spec; . venv/bin/activate; python -m pytest --junitxml=test-reports/eth2spec/test_results.xml .

 # "make pyspec" to create the pyspec for all phases.
 pyspec: $(PY_SPEC_ALL_TARGETS)
--- a/README.md
+++ b/README.md
@ -2,20 +2,20 @@

 [![Join the chat at https://gitter.im/ethereum/sharding](https://badges.gitter.im/ethereum/sharding.svg)](https://gitter.im/ethereum/sharding?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)

-To learn more about sharding and eth2.0/Serenity, see the [sharding FAQ](https://github.com/ethereum/wiki/wiki/Sharding-FAQ) and the [research compendium](https://notes.ethereum.org/s/H1PGqDhpm).
+To learn more about sharding and Ethereum 2.0 (Serenity), see the [sharding FAQ](https://github.com/ethereum/wiki/wiki/Sharding-FAQ) and the [research compendium](https://notes.ethereum.org/s/H1PGqDhpm).

-This repo hosts the current eth2.0 specifications. Discussions about design rationale and proposed changes can be brought up and discussed as issues. Solidified, agreed upon changes to spec can be made through pull requests.
+This repository hosts the current Eth 2.0 specifications. Discussions about design rationale and proposed changes can be brought up and discussed as issues. Solidified, agreed-upon changes to the spec can be made through pull requests.


 ## Specs

-Core specifications for eth2.0 client validation can be found in [specs/core](specs/core). These are divided into phases. Each subsequent phase depends upon the prior. The current phases specified are:
+Core specifications for Eth 2.0 client validation can be found in [specs/core](specs/core). These are divided into phases. Each subsequent phase depends upon the prior. The current phases specified are:

 ### Phase 0
 * [The Beacon Chain](specs/core/0_beacon-chain.md)
 * [Fork Choice](specs/core/0_fork-choice.md)
 * [Deposit Contract](specs/core/0_deposit-contract.md)
-* [Honest validator implementation doc](specs/validator/0_beacon-chain-validator.md)
+* [Honest Validator](specs/validator/0_beacon-chain-validator.md)

 ### Phase 1
 * [Custody Game](specs/core/1_custody-game.md)
@ -30,7 +30,7 @@ Core specifications for eth2.0 client validation can be found in [specs/core](sp
 * [Light client syncing protocol](specs/light_client/sync_protocol.md)


-### Design goals
+## Design goals

 The following are the broad design goals for Ethereum 2.0:
 * to minimize complexity, even at the cost of some losses in efficiency
--- a/configs/constant_presets/README.md
+++ b/configs/constant_presets/README.md
@ -10,11 +10,11 @@ Later-fork constants can be ignored, e.g. ignore phase1 constants as a client th
 Each preset is a key-value mapping.

 **Key**: an `UPPER_SNAKE_CASE` (a.k.a. "macro case") formatted string, name of the constant.
-**Value**: can be any of:
+
+**Value** can be either:
 - an unsigned integer number, can be up to 64 bits (incl.)
 - a hexadecimal string, prefixed with `0x`

 Presets may contain comments to describe the values.

-See `mainnet.yaml` for a complete example.
-
+See [`mainnet.yaml`](./mainnet.yaml) for a complete example.
--- a/configs/constant_presets/mainnet.yaml
+++ b/configs/constant_presets/mainnet.yaml
@ -15,6 +15,8 @@ MAX_INDICES_PER_ATTESTATION: 4096
 MIN_PER_EPOCH_CHURN_LIMIT: 4
 # 2**16 (= 65,536)
 CHURN_LIMIT_QUOTIENT: 65536
+# Normalizes base rewards
+BASE_REWARDS_PER_EPOCH: 5
 # See issue 563
 SHUFFLE_ROUND_COUNT: 90

@ -36,7 +38,7 @@ MAX_EFFECTIVE_BALANCE: 32000000000
 # 2**4 * 10**9 (= 16,000,000,000) Gwei
 EJECTION_BALANCE: 16000000000
 # 2**0 * 10**9 (= 1,000,000,000) Gwei
-HIGH_BALANCE_INCREMENT: 1000000000
+EFFECTIVE_BALANCE_INCREMENT: 1000000000


 # Initial values
@ -71,6 +73,8 @@ MIN_VALIDATOR_WITHDRAWABILITY_DELAY: 256
 PERSISTENT_COMMITTEE_PERIOD: 2048
 # 2**6 (= 64) epochs ~7 hours
 MAX_CROSSLINK_EPOCHS: 64
+# 2**2 (= 4) epochs 25.6 minutes
+MIN_EPOCHS_TO_INACTIVITY_PENALTY: 4


 # State list lengths
@ -91,14 +95,14 @@ BASE_REWARD_QUOTIENT: 32
 WHISTLEBLOWING_REWARD_QUOTIENT: 512
 # 2**3 (= 8)
 PROPOSER_REWARD_QUOTIENT: 8
-# 2**24 (= 16,777,216)
-INACTIVITY_PENALTY_QUOTIENT: 16777216
+# 2**25 (= 33,554,432)
+INACTIVITY_PENALTY_QUOTIENT: 33554432
+# 2**5 (= 32)
+MIN_SLASHING_PENALTY_QUOTIENT: 32


 # Max operations per block
 # ---------------------------------------------------------------
-# 2**5 (= 32)
-MIN_PENALTY_QUOTIENT: 32
 # 2**4 (= 16)
 MAX_PROPOSER_SLASHINGS: 16
 # 2**0 (= 1)
--- a/configs/constant_presets/minimal.yaml
+++ b/configs/constant_presets/minimal.yaml
@ -6,7 +6,6 @@

 # [customized] Just 8 shards for testing purposes
 SHARD_COUNT: 8
-
 # [customized] unsecure, but fast
 TARGET_COMMITTEE_SIZE: 4
 # 2**12 (= 4,096)
@ -15,6 +14,8 @@ MAX_INDICES_PER_ATTESTATION: 4096
 MIN_PER_EPOCH_CHURN_LIMIT: 4
 # 2**16 (= 65,536)
 CHURN_LIMIT_QUOTIENT: 65536
+# Normalizes base rewards
+BASE_REWARDS_PER_EPOCH: 5
 # [customized] Faster, but unsecure.
 SHUFFLE_ROUND_COUNT: 10

@ -36,7 +37,7 @@ MAX_EFFECTIVE_BALANCE: 32000000000
 # 2**4 * 10**9 (= 16,000,000,000) Gwei
 EJECTION_BALANCE: 16000000000
 # 2**0 * 10**9 (= 1,000,000,000) Gwei
-HIGH_BALANCE_INCREMENT: 1000000000
+EFFECTIVE_BALANCE_INCREMENT: 1000000000


 # Initial values
@ -71,6 +72,8 @@ MIN_VALIDATOR_WITHDRAWABILITY_DELAY: 256
 PERSISTENT_COMMITTEE_PERIOD: 2048
 # 2**6 (= 64) epochs ~7 hours
 MAX_CROSSLINK_EPOCHS: 64
+# 2**2 (= 4) epochs 25.6 minutes
+MIN_EPOCHS_TO_INACTIVITY_PENALTY: 4


 # State list lengths
@ -91,14 +94,14 @@ BASE_REWARD_QUOTIENT: 32
 WHISTLEBLOWING_REWARD_QUOTIENT: 512
 # 2**3 (= 8)
 PROPOSER_REWARD_QUOTIENT: 8
-# 2**24 (= 16,777,216)
-INACTIVITY_PENALTY_QUOTIENT: 16777216
+# 2**25 (= 33,554,432)
+INACTIVITY_PENALTY_QUOTIENT: 33554432
+# 2**5 (= 32)
+MIN_SLASHING_PENALTY_QUOTIENT: 32


 # Max operations per block
 # ---------------------------------------------------------------
-# 2**5 (= 32)
-MIN_PENALTY_QUOTIENT: 32
 # 2**4 (= 16)
 MAX_PROPOSER_SLASHINGS: 16
 # 2**0 (= 1)
--- a/configs/fork_timelines/README.md
+++ b/configs/fork_timelines/README.md
@ -3,16 +3,17 @@
 This directory contains a set of fork timelines used for testing, testnets, and mainnet.

 A timeline file contains all the forks known for its target.
-Later forks can be ignored, e.g. ignore fork `phase1` as a client that only supports phase 0 currently.
+Later forks can be ignored, e.g. ignore fork `phase1` as a client that only supports Phase 0 currently.

 ## Format

 Each preset is a key-value mapping.

 **Key**: an `lower_snake_case` (a.k.a. "python case") formatted string, name of the fork.
-**Value**: an unsigned integer number, epoch number of activation of the fork
+
+**Value**: an unsigned integer number, epoch number of activation of the fork.

 Timelines may contain comments to describe the values.

-See `mainnet.yaml` for a complete example.
+See [`mainnet.yaml`](./mainnet.yaml) for a complete example.

--- a/scripts/phase0/build_spec.py
+++ b/scripts/phase0/build_spec.py
@ -5,10 +5,8 @@ import function_puller
 def build_phase0_spec(sourcefile, outfile):
    code_lines = []
    code_lines.append("""
-    
 from typing import (
    Any,
-    Callable,
    Dict,
    List,
    NewType,
@ -17,19 +15,16 @@ from typing import (
 from eth2spec.utils.minimal_ssz import *
 from eth2spec.utils.bls_stub import *

-
-    """)
+""")
    for i in (1, 2, 3, 4, 8, 32, 48, 96):
        code_lines.append("def int_to_bytes%d(x): return x.to_bytes(%d, 'little')" % (i, i))

    code_lines.append("""
+
 # stub, will get overwritten by real var
 SLOTS_PER_EPOCH = 64


-def slot_to_epoch(x): return x // SLOTS_PER_EPOCH
-
-
 Slot = NewType('Slot', int)  # uint64
 Epoch = NewType('Epoch', int)  # uint64
 Shard = NewType('Shard', int)  # uint64
@ -38,31 +33,24 @@ Gwei = NewType('Gwei', int)  # uint64
 Bytes32 = NewType('Bytes32', bytes)  # bytes32
 BLSPubkey = NewType('BLSPubkey', bytes)  # bytes48
 BLSSignature = NewType('BLSSignature', bytes)  # bytes96
-Any = None
 Store = None
-    """)
+""")

    code_lines += function_puller.get_spec(sourcefile)

    code_lines.append("""
-# Monkey patch validator get committee code
+# Monkey patch validator compute committee code
 _compute_committee = compute_committee
 committee_cache = {}


-def compute_committee(validator_indices: List[ValidatorIndex],
-                      seed: Bytes32,
-                      index: int,
-                      total_committees: int) -> List[ValidatorIndex]:
-
-    param_hash = (hash_tree_root(validator_indices), seed, index, total_committees)
+def compute_committee(indices: List[ValidatorIndex], seed: Bytes32, index: int, count: int) -> List[ValidatorIndex]:
+    param_hash = (hash_tree_root(indices), seed, index, count)

    if param_hash in committee_cache:
-        # print("Cache hit, epoch={0}".format(epoch))
        return committee_cache[param_hash]
    else:
-        # print("Cache miss, epoch={0}".format(epoch))
-        ret = _compute_committee(validator_indices, seed, index, total_committees)
+        ret = _compute_committee(indices, seed, index, count)
        committee_cache[param_hash] = ret
        return ret

@ -88,7 +76,7 @@ def apply_constants_preset(preset: Dict[str, Any]):

    # Deal with derived constants
    global_vars['GENESIS_EPOCH'] = slot_to_epoch(GENESIS_SLOT)
-    
+
    # Initialize SSZ types again, to account for changed lengths
    init_SSZ_types()
 """)
--- a/scripts/phase0/function_puller.py
+++ b/scripts/phase0/function_puller.py
@ -62,9 +62,10 @@ def get_spec(file_name: str) -> List[str]:
        code_lines.append('')
        for type_line in ssz_type:
            code_lines.append('    ' + type_line)
-    code_lines.append('')
+    code_lines.append('\n')
    code_lines.append('ssz_types = [' + ', '.join([f'\'{ssz_type_name}\'' for (ssz_type_name, _) in type_defs]) + ']')
-    code_lines.append('')
-    code_lines.append('def get_ssz_type_by_name(name: str) -> SSZType: return globals()[name]')
+    code_lines.append('\n')
+    code_lines.append('def get_ssz_type_by_name(name: str) -> SSZType:')
+    code_lines.append('    return globals()[name]')
    code_lines.append('')
    return code_lines
--- a/specs/bls_signature.md
+++ b/specs/bls_signature.md
@ -118,7 +118,7 @@ Let `bls_aggregate_signatures(signatures: List[Bytes96]) -> Bytes96` return `sig

 ## Signature verification

-In the following `e` is the pairing function and `g` is the G1 generator with the following coordinates (see [here](https://github.com/zkcrypto/pairing/tree/master/src/bls12_381#g1)):
+In the following, `e` is the pairing function and `g` is the G1 generator with the following coordinates (see [here](https://github.com/zkcrypto/pairing/tree/master/src/bls12_381#g1)):

 ```python
 g_x = 3685416753713387016781088315183077757961620795782546409894578378688607592378376318836054947676345821548104185464507
--- a/specs/core/0_beacon-chain.md
+++ b/specs/core/0_beacon-chain.md
@ -1,6 +1,6 @@
 # Ethereum 2.0 Phase 0 -- The Beacon Chain

-**NOTICE**: This document is a work in progress for researchers and implementers.
+**Notice**: This document is a work-in-progress for researchers and implementers.

 ## Table of contents
 <!-- TOC -->
@ -45,7 +45,7 @@
            - [`BeaconBlock`](#beaconblock)
        - [Beacon state](#beacon-state)
            - [`BeaconState`](#beaconstate)
-    - [Custom Types](#custom-types)
+    - [Custom types](#custom-types)
    - [Helper functions](#helper-functions)
        - [`xor`](#xor)
        - [`hash`](#hash)
@ -60,20 +60,20 @@
        - [`get_active_validator_indices`](#get_active_validator_indices)
        - [`increase_balance`](#increase_balance)
        - [`decrease_balance`](#decrease_balance)
-        - [`get_permuted_index`](#get_permuted_index)
-        - [`get_split_offset`](#get_split_offset)
        - [`get_epoch_committee_count`](#get_epoch_committee_count)
        - [`get_shard_delta`](#get_shard_delta)
-        - [`compute_committee`](#compute_committee)
-        - [`get_crosslink_committees_at_slot`](#get_crosslink_committees_at_slot)
+        - [`get_epoch_start_shard`](#get_epoch_start_shard)
+        - [`get_attestation_data_slot`](#get_attestation_data_slot)
        - [`get_block_root_at_slot`](#get_block_root_at_slot)
        - [`get_block_root`](#get_block_root)
-        - [`get_state_root`](#get_state_root)
        - [`get_randao_mix`](#get_randao_mix)
        - [`get_active_index_root`](#get_active_index_root)
        - [`generate_seed`](#generate_seed)
        - [`get_beacon_proposer_index`](#get_beacon_proposer_index)
        - [`verify_merkle_branch`](#verify_merkle_branch)
+        - [`get_shuffled_index`](#get_shuffled_index)
+        - [`compute_committee`](#compute_committee)
+        - [`get_crosslink_committee`](#get_crosslink_committee)
        - [`get_attesting_indices`](#get_attesting_indices)
        - [`int_to_bytes1`, `int_to_bytes2`, ...](#int_to_bytes1-int_to_bytes2-)
        - [`bytes_to_int`](#bytes_to_int)
@ -83,8 +83,7 @@
        - [`verify_bitfield`](#verify_bitfield)
        - [`convert_to_indexed`](#convert_to_indexed)
        - [`verify_indexed_attestation`](#verify_indexed_attestation)
-        - [`is_double_vote`](#is_double_vote)
-        - [`is_surround_vote`](#is_surround_vote)
+        - [`is_slashable_attestation_data`](#is_slashable_attestation_data)
        - [`integer_squareroot`](#integer_squareroot)
        - [`get_delayed_activation_exit_epoch`](#get_delayed_activation_exit_epoch)
        - [`get_churn_limit`](#get_churn_limit)
@ -94,7 +93,10 @@
        - [Routines for updating validator status](#routines-for-updating-validator-status)
            - [`initiate_validator_exit`](#initiate_validator_exit)
            - [`slash_validator`](#slash_validator)
-    - [On genesis](#on-genesis)
+    - [Genesis](#genesis)
+        - [`Eth2Genesis`](#eth2genesis)
+        - [Genesis state](#genesis-state)
+        - [Genesis block](#genesis-block)
    - [Beacon chain state transition function](#beacon-chain-state-transition-function)
        - [State caching](#state-caching)
        - [Per-epoch processing](#per-epoch-processing)
@ -135,25 +137,25 @@ Code snippets appearing in `this style` are to be interpreted as Python code.

 ## Terminology

-* **Validator** <a id="dfn-validator"></a> - a registered participant in the beacon chain. You can become one by sending ether into the Ethereum 1.0 deposit contract.
-* **Active validator** <a id="dfn-active-validator"></a> - an active participant in the Ethereum 2.0 consensus invited to, among other things, propose and attest to blocks and vote for crosslinks.
-* **Committee** - a (pseudo-) randomly sampled subset of [active validators](#dfn-active-validator). When a committee is referred to collectively, as in "this committee attests to X", this is assumed to mean "some subset of that committee that contains enough [validators](#dfn-validator) that the protocol recognizes it as representing the committee".
-* **Proposer** - the [validator](#dfn-validator) that creates a beacon chain block.
-* **Attester** - a [validator](#dfn-validator) that is part of a committee that needs to sign off on a beacon chain block while simultaneously creating a link (crosslink) to a recent shard block on a particular shard chain.
-* **Beacon chain** - the central PoS chain that is the base of the sharding system.
-* **Shard chain** - one of the chains on which user transactions take place and account data is stored.
-* **Block root** - a 32-byte Merkle root of a beacon chain block or shard chain block. Previously called "block hash".
-* **Crosslink** - a set of signatures from a committee attesting to a block in a shard chain that can be included into the beacon chain. Crosslinks are the main means by which the beacon chain "learns about" the updated state of shard chains.
-* **Slot** - a period during which one proposer has the ability to create a beacon chain block and some attesters have the ability to make attestations.
-* **Epoch** - an aligned span of slots during which all [validators](#dfn-validator) get exactly one chance to make an attestation.
-* **Finalized**, **justified** - see the [Casper FFG paper](https://arxiv.org/abs/1710.09437).
-* **Withdrawal period** - the number of slots between a [validator](#dfn-validator) exit and the [validator](#dfn-validator) balance being withdrawable.
-* **Genesis time** - the Unix time of the genesis beacon chain block at slot 0.
+* **Validator**<a id="dfn-validator"></a>—a registered participant in the beacon chain. You can become one by sending ether into the Ethereum 1.0 deposit contract.
+* **Active validator**<a id="dfn-active-validator"></a>—an active participant in the Ethereum 2.0 consensus invited to, among other things, propose and attest to blocks and vote for crosslinks.
+* **Committee**—a (pseudo-) randomly sampled subset of [active validators](#dfn-active-validator). When a committee is referred to collectively, as in "this committee attests to X", this is assumed to mean "some subset of that committee that contains enough [validators](#dfn-validator) that the protocol recognizes it as representing the committee".
+* **Proposer**—the [validator](#dfn-validator) that creates a beacon chain block.
+* **Attester**—a [validator](#dfn-validator) that is part of a committee that needs to sign off on a beacon chain block while simultaneously creating a link (crosslink) to a recent shard block on a particular shard chain.
+* **Beacon chain**—the central PoS chain that is the base of the sharding system.
+* **Shard chain**—one of the chains on which user transactions take place and account data is stored.
+* **Block root**—a 32-byte Merkle root of a beacon chain block or shard chain block. Previously called "block hash".
+* **Crosslink**—a set of signatures from a committee attesting to a block in a shard chain that can be included into the beacon chain. Crosslinks are the main means by which the beacon chain "learns about" the updated state of shard chains.
+* **Slot**—a period during which one proposer has the ability to create a beacon chain block and some attesters have the ability to make attestations.
+* **Epoch**—an aligned span of slots during which all [validators](#dfn-validator) get exactly one chance to make an attestation.
+* **Finalized**, **justified**—see the [Casper FFG paper](https://arxiv.org/abs/1710.09437).
+* **Withdrawal period**—the number of slots between a [validator](#dfn-validator) exit and the [validator](#dfn-validator) balance being withdrawable.
+* **Genesis time**—the Unix time of the genesis beacon chain block at slot 0.

 ## Constants

-Note: the default mainnet values for the constants are included here for spec-design purposes.
-The different configurations for mainnet, testnets, and yaml-based testing can be found in the `configs/constant_presets/` directory.
+*Note*: The default mainnet values for the constants are included here for spec-design purposes.
+The different configurations for mainnet, testnets, and YAML-based testing can be found in the `configs/constant_presets/` directory.
 These configurations are updated for releases, but may be out of sync during `dev` changes.

 ### Misc
@ -166,7 +168,7 @@ These configurations are updated for releases, but may be out of sync during `de
 | `MIN_PER_EPOCH_CHURN_LIMIT` | `2**2` (= 4) |
 | `CHURN_LIMIT_QUOTIENT` | `2**16` (= 65,536) |
 | `BASE_REWARDS_PER_EPOCH` | `5` |
-| `SHUFFLE_ROUND_COUNT` | 90 |
+| `SHUFFLE_ROUND_COUNT` | `90` |

 * For the safety of crosslinks `TARGET_COMMITTEE_SIZE` exceeds [the recommended minimum committee size of 111](https://vitalik.ca/files/Ithaca201807_Sharding.pdf); with sufficient active validators (at least `SLOTS_PER_EPOCH * TARGET_COMMITTEE_SIZE`), the shuffling algorithm ensures committee sizes of at least `TARGET_COMMITTEE_SIZE`. (Unbiasable randomness with a Verifiable Delay Function (VDF) will improve committee robustness and lower the safe minimum committee size.)

@ -230,7 +232,7 @@ These configurations are updated for releases, but may be out of sync during `de
 | `INACTIVITY_PENALTY_QUOTIENT` | `2**25` (= 33,554,432) |
 | `MIN_SLASHING_PENALTY_QUOTIENT` | `2**5` (= 32) |

-* **The `BASE_REWARD_QUOTIENT` is NOT final. Once all other protocol details are finalized it will be adjusted, to target a theoretical maximum total issuance of `2**21` ETH per year if `2**27` ETH is validating (and therefore `2**20` per year if `2**25` ETH is validating, etc etc)**
+* **The `BASE_REWARD_QUOTIENT` is NOT final. Once all other protocol details are finalized, it will be adjusted to target a theoretical maximum total issuance of `2**21` ETH per year if `2**27` ETH is validating (and therefore `2**20` per year if `2**25` ETH is validating, etc.)**
 * The `INACTIVITY_PENALTY_QUOTIENT` equals `INVERSE_SQRT_E_DROP_TIME**2` where `INVERSE_SQRT_E_DROP_TIME := 2**12 epochs` (~18 days) is the time it takes the inactivity penalty to reduce the balance of non-participating [validators](#dfn-validator) to about `1/sqrt(e) ~= 60.6%`. Indeed, the balance retained by offline [validators](#dfn-validator) after `n` epochs is about `(1 - 1/INACTIVITY_PENALTY_QUOTIENT)**(n**2/2)` so after `INVERSE_SQRT_E_DROP_TIME` epochs it is roughly `(1 - 1/INACTIVITY_PENALTY_QUOTIENT)**(INACTIVITY_PENALTY_QUOTIENT/2) ~= 1/sqrt(e)`.

 ### Max operations per block
@ -307,12 +309,12 @@ The types are defined topologically to aid in facilitating an executable version
 ```python
 {
    # LMD GHOST vote
-    'slot': 'uint64',
    'beacon_block_root': 'bytes32',

    # FFG vote
    'source_epoch': 'uint64',
    'source_root': 'bytes32',
+    'target_epoch': 'uint64',
    'target_root': 'bytes32',

    # Crosslink vote
@ -404,8 +406,8 @@ The types are defined topologically to aid in facilitating an executable version
    'aggregation_bitfield': 'bytes',
    # Attestation data
    'data': AttestationData,
-    # Inclusion slot
-    'inclusion_slot': 'uint64',
+    # Inclusion delay
+    'inclusion_delay': 'uint64',
    # Proposer index
    'proposer_index': 'uint64',
 }
@ -518,6 +520,7 @@ The types are defined topologically to aid in facilitating an executable version
 {
    'randao_reveal': 'bytes96',
    'eth1_data': Eth1Data,
+    'graffiti': 'bytes32',
    'proposer_slashings': [ProposerSlashing],
    'attester_slashings': [AttesterSlashing],
    'attestations': [Attestation],
@ -587,7 +590,7 @@ The types are defined topologically to aid in facilitating an executable version
 }
 ```

-## Custom Types
+## Custom types

 We define the following Python custom types for type hinting and readability:

@ -604,7 +607,7 @@ We define the following Python custom types for type hinting and readability:

 ## Helper functions

-Note: The definitions below are for specification purposes and are not necessarily optimal implementations.
+*Note*: The definitions below are for specification purposes and are not necessarily optimal implementations.

 ### `xor`

@ -617,7 +620,7 @@ def xor(bytes1: Bytes32, bytes2: Bytes32) -> Bytes32:

 The `hash` function is SHA256.

-Note: We aim to migrate to a S[T/N]ARK-friendly hash function in a future Ethereum 2.0 deployment phase.
+*Note*: We aim to migrate to a S[T/N]ARK-friendly hash function in a future Ethereum 2.0 deployment phase.

 ### `hash_tree_root`

@ -687,7 +690,6 @@ def is_slashable_validator(validator: Validator, epoch: Epoch) -> bool:
    Check if ``validator`` is slashable.
    """
    return validator.slashed is False and (validator.activation_epoch <= epoch < validator.withdrawable_epoch)
-
 ```

 ### `get_active_validator_indices`
@ -720,43 +722,6 @@ def decrease_balance(state: BeaconState, index: ValidatorIndex, delta: Gwei) ->
    state.balances[index] = 0 if delta > state.balances[index] else state.balances[index] - delta
 ```

-### `get_permuted_index`
-
-```python
-def get_permuted_index(index: int, list_size: int, seed: Bytes32) -> int:
-    """
-    Return `p(index)` in a pseudorandom permutation `p` of `0...list_size - 1` with ``seed`` as entropy.
-
-    Utilizes 'swap or not' shuffling found in
-    https://link.springer.com/content/pdf/10.1007%2F978-3-642-32009-5_1.pdf
-    See the 'generalized domain' algorithm on page 3.
-    """
-    assert index < list_size
-    assert list_size <= 2**40
-
-    for round in range(SHUFFLE_ROUND_COUNT):
-        pivot = bytes_to_int(hash(seed + int_to_bytes1(round))[0:8]) % list_size
-        flip = (pivot - index) % list_size
-        position = max(index, flip)
-        source = hash(seed + int_to_bytes1(round) + int_to_bytes4(position // 256))
-        byte = source[(position % 256) // 8]
-        bit = (byte >> (position % 8)) % 2
-        index = flip if bit else index
-
-    return index
-```
-
-### `get_split_offset`
-
-```python
-def get_split_offset(list_size: int, chunks: int, index: int) -> int:
-    """
-    Returns a value such that for a list L, chunk count k and index i,
-    split(L, k)[i] == L[get_split_offset(len(L), k, i): get_split_offset(len(L), k, i+1)]
-    """
-    return (list_size * index) // chunks
-```
-
 ### `get_epoch_committee_count`

 ```python
@ -784,65 +749,26 @@ def get_shard_delta(state: BeaconState, epoch: Epoch) -> int:
    return min(get_epoch_committee_count(state, epoch), SHARD_COUNT - SHARD_COUNT // SLOTS_PER_EPOCH)
 ```

-### `compute_committee`
+### `get_epoch_start_shard`

 ```python
-def compute_committee(validator_indices: List[ValidatorIndex],
-                      seed: Bytes32,
-                      index: int,
-                      total_committees: int) -> List[ValidatorIndex]:
-    """
-    Return the ``index``'th shuffled committee out of a total ``total_committees``
-    using ``validator_indices`` and ``seed``.
-    """
-    start_offset = get_split_offset(len(validator_indices), total_committees, index)
-    end_offset = get_split_offset(len(validator_indices), total_committees, index + 1)
-    return [
-        validator_indices[get_permuted_index(i, len(validator_indices), seed)]
-        for i in range(start_offset, end_offset)
-    ]
+def get_epoch_start_shard(state: BeaconState, epoch: Epoch) -> Shard:
+    assert epoch <= get_current_epoch(state) + 1
+    check_epoch = get_current_epoch(state) + 1
+    shard = (state.latest_start_shard + get_shard_delta(state, get_current_epoch(state))) % SHARD_COUNT
+    while check_epoch > epoch:
+        check_epoch -= 1
+        shard = (shard + SHARD_COUNT - get_shard_delta(state, check_epoch)) % SHARD_COUNT
+    return shard
 ```

-Note: this definition and the next few definitions are highly inefficient as algorithms, as they re-calculate many sub-expressions. Production implementations are expected to appropriately use caching/memoization to avoid redoing work.
-
-### `get_crosslink_committees_at_slot`
+### `get_attestation_data_slot`

 ```python
-def get_crosslink_committees_at_slot(state: BeaconState,
-                                     slot: Slot) -> List[Tuple[List[ValidatorIndex], Shard]]:
-    """
-    Return the list of ``(committee, shard)`` tuples for the ``slot``.
-    """
-    epoch = slot_to_epoch(slot)
-    current_epoch = get_current_epoch(state)
-    previous_epoch = get_previous_epoch(state)
-    next_epoch = current_epoch + 1
-
-    assert previous_epoch <= epoch <= next_epoch
-    indices = get_active_validator_indices(state, epoch)
-
-    if epoch == current_epoch:
-        start_shard = state.latest_start_shard
-    elif epoch == previous_epoch:
-        previous_shard_delta = get_shard_delta(state, previous_epoch)
-        start_shard = (state.latest_start_shard - previous_shard_delta) % SHARD_COUNT
-    elif epoch == next_epoch:
-        current_shard_delta = get_shard_delta(state, current_epoch)
-        start_shard = (state.latest_start_shard + current_shard_delta) % SHARD_COUNT
-
-    committees_per_epoch = get_epoch_committee_count(state, epoch)
-    committees_per_slot = committees_per_epoch // SLOTS_PER_EPOCH
-    offset = slot % SLOTS_PER_EPOCH
-    slot_start_shard = (start_shard + committees_per_slot * offset) % SHARD_COUNT
-    seed = generate_seed(state, epoch)
-
-    return [
-        (
-            compute_committee(indices, seed, committees_per_slot * offset + i, committees_per_epoch),
-            (slot_start_shard + i) % SHARD_COUNT,
-        )
-        for i in range(committees_per_slot)
-    ]
+def get_attestation_data_slot(state: BeaconState, data: AttestationData) -> Slot:
+    committee_count = get_epoch_committee_count(state, data.target_epoch)
+    offset = (data.shard + SHARD_COUNT - get_epoch_start_shard(state, data.target_epoch)) % SHARD_COUNT
+    return get_epoch_start_slot(data.target_epoch) + offset // (committee_count // SLOTS_PER_EPOCH)
 ```

 ### `get_block_root_at_slot`
@ -868,18 +794,6 @@ def get_block_root(state: BeaconState,
    return get_block_root_at_slot(state, get_epoch_start_slot(epoch))
 ```

-### `get_state_root`
-
-```python
-def get_state_root(state: BeaconState,
-                   slot: Slot) -> Bytes32:
-    """
-    Return the state root at a recent ``slot``.
-    """
-    assert slot < state.slot <= slot + SLOTS_PER_HISTORICAL_ROOT
-    return state.latest_state_roots[slot % SLOTS_PER_HISTORICAL_ROOT]
-```
-
 ### `get_randao_mix`

 ```python
@ -887,8 +801,8 @@ def get_randao_mix(state: BeaconState,
                   epoch: Epoch) -> Bytes32:
    """
    Return the randao mix at a recent ``epoch``.
+    ``epoch`` expected to be between (current_epoch - LATEST_RANDAO_MIXES_LENGTH, current_epoch].
    """
-    assert get_current_epoch(state) - LATEST_RANDAO_MIXES_LENGTH < epoch <= get_current_epoch(state)
    return state.latest_randao_mixes[epoch % LATEST_RANDAO_MIXES_LENGTH]
 ```

@ -899,8 +813,9 @@ def get_active_index_root(state: BeaconState,
                          epoch: Epoch) -> Bytes32:
    """
    Return the index root at a recent ``epoch``.
+    ``epoch`` expected to be between
+    (current_epoch - LATEST_ACTIVE_INDEX_ROOTS_LENGTH + ACTIVATION_EXIT_DELAY, current_epoch + ACTIVATION_EXIT_DELAY].
    """
-    assert get_current_epoch(state) - LATEST_ACTIVE_INDEX_ROOTS_LENGTH + ACTIVATION_EXIT_DELAY < epoch <= get_current_epoch(state) + ACTIVATION_EXIT_DELAY
    return state.latest_active_index_roots[epoch % LATEST_ACTIVE_INDEX_ROOTS_LENGTH]
 ```

@ -913,7 +828,7 @@ def generate_seed(state: BeaconState,
    Generate a seed for the given ``epoch``.
    """
    return hash(
-        get_randao_mix(state, epoch - MIN_SEED_LOOKAHEAD) +
+        get_randao_mix(state, epoch + LATEST_RANDAO_MIXES_LENGTH - MIN_SEED_LOOKAHEAD) +
        get_active_index_root(state, epoch) +
        int_to_bytes32(epoch)
    )
@ -924,15 +839,19 @@ def generate_seed(state: BeaconState,
 ```python
 def get_beacon_proposer_index(state: BeaconState) -> ValidatorIndex:
    """
-    Return the beacon proposer index at ``state.slot``.
+    Return the current beacon proposer index.
    """
-    current_epoch = get_current_epoch(state)
-    first_committee, _ = get_crosslink_committees_at_slot(state, state.slot)[0]
+    epoch = get_current_epoch(state)
+    committees_per_slot = get_epoch_committee_count(state, epoch) // SLOTS_PER_EPOCH
+    offset = committees_per_slot * (state.slot % SLOTS_PER_EPOCH)
+    shard = (get_epoch_start_shard(state, epoch) + offset) % SHARD_COUNT
+    first_committee = get_crosslink_committee(state, epoch, shard)
    MAX_RANDOM_BYTE = 2**8 - 1
+    seed = generate_seed(state, epoch)
    i = 0
    while True:
-        candidate_index = first_committee[(current_epoch + i) % len(first_committee)]
-        random_byte = hash(generate_seed(state, current_epoch) + int_to_bytes8(i // 32))[i % 32]
+        candidate_index = first_committee[(epoch + i) % len(first_committee)]
+        random_byte = hash(seed + int_to_bytes8(i // 32))[i % 32]
        effective_balance = state.validator_registry[candidate_index].effective_balance
        if effective_balance * MAX_RANDOM_BYTE >= MAX_EFFECTIVE_BALANCE * random_byte:
            return candidate_index
@ -956,6 +875,51 @@ def verify_merkle_branch(leaf: Bytes32, proof: List[Bytes32], depth: int, index:
    return value == root
 ```

+### `get_shuffled_index`
+
+```python
+def get_shuffled_index(index: ValidatorIndex, index_count: int, seed: Bytes32) -> ValidatorIndex:
+    """
+    Return the shuffled validator index corresponding to ``seed`` (and ``index_count``).
+    """
+    assert index < index_count
+    assert index_count <= 2**40
+
+    # Swap or not (https://link.springer.com/content/pdf/10.1007%2F978-3-642-32009-5_1.pdf)
+    # See the 'generalized domain' algorithm on page 3
+    for round in range(SHUFFLE_ROUND_COUNT):
+        pivot = bytes_to_int(hash(seed + int_to_bytes1(round))[0:8]) % index_count
+        flip = (pivot - index) % index_count
+        position = max(index, flip)
+        source = hash(seed + int_to_bytes1(round) + int_to_bytes4(position // 256))
+        byte = source[(position % 256) // 8]
+        bit = (byte >> (position % 8)) % 2
+        index = flip if bit else index
+
+    return index
+```
+
+### `compute_committee`
+
+```python
+def compute_committee(indices: List[ValidatorIndex], seed: Bytes32, index: int, count: int) -> List[ValidatorIndex]:
+    start = (len(indices) * index) // count
+    end = (len(indices) * (index + 1)) // count
+    return [indices[get_shuffled_index(i, len(indices), seed)] for i in range(start, end)]
+```
+
+### `get_crosslink_committee`
+
+```python
+def get_crosslink_committee(state: BeaconState, epoch: Epoch, shard: Shard) -> List[ValidatorIndex]:
+    return compute_committee(
+        indices=get_active_validator_indices(state, epoch),
+        seed=generate_seed(state, epoch),
+        index=(shard + SHARD_COUNT - get_epoch_start_shard(state, epoch)) % SHARD_COUNT,
+        count=get_epoch_committee_count(state, epoch),
+    )
+```
+
 ### `get_attesting_indices`

 ```python
@ -965,10 +929,9 @@ def get_attesting_indices(state: BeaconState,
    """
    Return the sorted attesting indices corresponding to ``attestation_data`` and ``bitfield``.
    """
-    crosslink_committees = get_crosslink_committees_at_slot(state, attestation_data.slot)
-    crosslink_committee = [committee for committee, shard in crosslink_committees if shard == attestation_data.shard][0]
-    assert verify_bitfield(bitfield, len(crosslink_committee))
-    return sorted([index for i, index in enumerate(crosslink_committee) if get_bitfield_bit(bitfield, i) == 0b1])
+    committee = get_crosslink_committee(state, attestation_data.target_epoch, attestation_data.shard)
+    assert verify_bitfield(bitfield, len(committee))
+    return sorted([index for i, index in enumerate(committee) if get_bitfield_bit(bitfield, i) == 0b1])
 ```

 ### `int_to_bytes1`, `int_to_bytes2`, ...
@ -1088,37 +1051,23 @@ def verify_indexed_attestation(state: BeaconState, indexed_attestation: IndexedA
            hash_tree_root(AttestationDataAndCustodyBit(data=indexed_attestation.data, custody_bit=0b1)),
        ],
        signature=indexed_attestation.signature,
-        domain=get_domain(state, DOMAIN_ATTESTATION, slot_to_epoch(indexed_attestation.data.slot)),
+        domain=get_domain(state, DOMAIN_ATTESTATION, indexed_attestation.data.target_epoch),
    )
 ```

-### `is_double_vote`
+### `is_slashable_attestation_data`

 ```python
-def is_double_vote(attestation_data_1: AttestationData,
-                   attestation_data_2: AttestationData) -> bool:
+def is_slashable_attestation_data(data_1: AttestationData, data_2: AttestationData) -> bool:
    """
-    Check if ``attestation_data_1`` and ``attestation_data_2`` have the same target.
+    Check if ``data_1`` and ``data_2`` are slashable according to Casper FFG rules.
    """
-    target_epoch_1 = slot_to_epoch(attestation_data_1.slot)
-    target_epoch_2 = slot_to_epoch(attestation_data_2.slot)
-    return target_epoch_1 == target_epoch_2
-```
-
-### `is_surround_vote`
-
-```python
-def is_surround_vote(attestation_data_1: AttestationData,
-                     attestation_data_2: AttestationData) -> bool:
-    """
-    Check if ``attestation_data_1`` surrounds ``attestation_data_2``.
-    """
-    source_epoch_1 = attestation_data_1.source_epoch
-    source_epoch_2 = attestation_data_2.source_epoch
-    target_epoch_1 = slot_to_epoch(attestation_data_1.slot)
-    target_epoch_2 = slot_to_epoch(attestation_data_2.slot)
-
-    return source_epoch_1 < source_epoch_2 and target_epoch_2 < target_epoch_1
+    return (
+        # Double vote
+        (data_1 != data_2 and data_1.target_epoch == data_2.target_epoch) or
+        # Surround vote
+        (data_1.source_epoch < data_2.source_epoch and data_2.target_epoch < data_1.target_epoch)
+    )
 ```

 ### `integer_squareroot`
@ -1151,6 +1100,9 @@ def get_delayed_activation_exit_epoch(epoch: Epoch) -> Epoch:

 ```python
 def get_churn_limit(state: BeaconState) -> int:
+    """
+    Return the churn limit based on the active validator count.
+    """
    return max(
        MIN_PER_EPOCH_CHURN_LIMIT,
        len(get_active_validator_indices(state, get_current_epoch(state))) // CHURN_LIMIT_QUOTIENT
@ -1171,7 +1123,7 @@ def get_churn_limit(state: BeaconState) -> int:

 ### Routines for updating validator status

-Note: All functions in this section mutate `state`.
+*Note*: All functions in this section mutate `state`.

 #### `initiate_validator_exit`

@ -1179,7 +1131,6 @@ Note: All functions in this section mutate `state`.
 def initiate_validator_exit(state: BeaconState, index: ValidatorIndex) -> None:
    """
    Initiate the validator of the given ``index``.
-    Note that this function mutates ``state``.
    """
    # Return if validator already initiated exit
    validator = state.validator_registry[index]
@ -1204,7 +1155,6 @@ def initiate_validator_exit(state: BeaconState, index: ValidatorIndex) -> None:
 def slash_validator(state: BeaconState, slashed_index: ValidatorIndex, whistleblower_index: ValidatorIndex=None) -> None:
    """
    Slash the validator with index ``slashed_index``.
-    Note that this function mutates ``state``.
    """
    current_epoch = get_current_epoch(state)
    initiate_validator_exit(state, slashed_index)
@ -1223,38 +1173,38 @@ def slash_validator(state: BeaconState, slashed_index: ValidatorIndex, whistlebl
    decrease_balance(state, slashed_index, whistleblowing_reward)
 ```

-## On genesis
+## Genesis

-When enough full deposits have been made to the deposit contract, an `Eth2Genesis` log is emitted. Construct a corresponding `genesis_state` and `genesis_block` as follows:
+### `Eth2Genesis`

-* Let `genesis_validator_deposits` be the list of deposits, ordered chronologically, up to and including the deposit that triggered the `Eth2Genesis` log.
-* Let `genesis_time` be the timestamp specified in the `Eth2Genesis` log.
-* Let `genesis_eth1_data` be the `Eth1Data` object where:
-    * `genesis_eth1_data.deposit_root` is the `deposit_root` contained in the `Eth2Genesis` log.
-    * `genesis_eth1_data.deposit_count` is the `deposit_count` contained in the `Eth2Genesis` log.
-    * `genesis_eth1_data.block_hash` is the hash of the Ethereum 1.0 block that emitted the `Eth2Genesis` log.
-* Let `genesis_state = get_genesis_beacon_state(genesis_validator_deposits, genesis_time, genesis_eth1_data)`.
-* Let `genesis_block = BeaconBlock(state_root=hash_tree_root(genesis_state))`.
+When enough deposits of size `MAX_EFFECTIVE_BALANCE` have been made to the deposit contract an `Eth2Genesis` log is emitted triggering the genesis of the beacon chain. Let:
+
+* `eth2genesis` be the object corresponding to `Eth2Genesis`
+* `genesis_eth1_data` be object of type `Eth1Data` where
+    * `genesis_eth1_data.deposit_root = eth2genesis.deposit_root`
+    * `genesis_eth1_data.deposit_count = eth2genesis.deposit_count`
+    * `genesis_eth1_data.block_hash` is the hash of the Ethereum 1.0 block that emitted the `Eth2Genesis` log
+* `genesis_deposits` be the object of type `List[Deposit]` with deposits ordered chronologically up to and including the deposit that triggered the `Eth2Genesis` log
+
+### Genesis state
+
+Let `genesis_state = get_genesis_beacon_state(genesis_deposits, eth2genesis.genesis_time, genesis_eth1_data)`.

 ```python
-def get_genesis_beacon_state(genesis_validator_deposits: List[Deposit],
-                             genesis_time: int,
-                             genesis_eth1_data: Eth1Data) -> BeaconState:
-    """
-    Get the genesis ``BeaconState``.
-    """
+def get_genesis_beacon_state(deposits: List[Deposit], genesis_time: int, genesis_eth1_data: Eth1Data) -> BeaconState:
    state = BeaconState(genesis_time=genesis_time, latest_eth1_data=genesis_eth1_data)

    # Process genesis deposits
-    for deposit in genesis_validator_deposits:
+    for deposit in deposits:
        process_deposit(state, deposit)

    # Process genesis activations
-    for index, validator in enumerate(state.validator_registry):
+    for validator in state.validator_registry:
        if validator.effective_balance >= MAX_EFFECTIVE_BALANCE:
            validator.activation_eligibility_epoch = GENESIS_EPOCH
            validator.activation_epoch = GENESIS_EPOCH

+    # Populate latest_active_index_roots
    genesis_active_index_root = hash_tree_root(get_active_validator_indices(state, GENESIS_EPOCH))
    for index in range(LATEST_ACTIVE_INDEX_ROOTS_LENGTH):
        state.latest_active_index_roots[index] = genesis_active_index_root
@ -1262,6 +1212,10 @@ def get_genesis_beacon_state(genesis_validator_deposits: List[Deposit],
    return state
 ```

+### Genesis block
+
+Let `genesis_block = BeaconBlock(state_root=hash_tree_root(genesis_state))`.
+
 ## Beacon chain state transition function

 We now define the state transition function. At a high level, the state transition is made up of four parts:
@ -1279,7 +1233,7 @@ Transition section notes:

 Beacon blocks that trigger unhandled Python exceptions (e.g. out-of-range list accesses) and failed `assert`s during the state transition are considered invalid.

-Note: If there are skipped slots between a block and its parent block, run the steps in the [state-root](#state-caching), [per-epoch](#per-epoch-processing), and [per-slot](#per-slot-processing) sections once for each skipped slot and then once for the slot containing the new block.
+*Note*: If there are skipped slots between a block and its parent block, run the steps in the [state-root](#state-caching), [per-epoch](#per-epoch-processing), and [per-slot](#per-slot-processing) sections once for each skipped slot and then once for the slot containing the new block.

 ### State caching

@ -1331,7 +1285,7 @@ def get_matching_target_attestations(state: BeaconState, epoch: Epoch) -> List[P
 def get_matching_head_attestations(state: BeaconState, epoch: Epoch) -> List[PendingAttestation]:
    return [
        a for a in get_matching_source_attestations(state, epoch)
-        if a.data.beacon_block_root == get_block_root_at_slot(state, a.data.slot)
+        if a.data.beacon_block_root == get_block_root_at_slot(state, get_attestation_data_slot(state, a.data))
    ]
 ```

@ -1351,14 +1305,14 @@ def get_attesting_balance(state: BeaconState, attestations: List[PendingAttestat
 ```python
 def get_crosslink_from_attestation_data(state: BeaconState, data: AttestationData) -> Crosslink:
    return Crosslink(
-        epoch=min(slot_to_epoch(data.slot), state.current_crosslinks[data.shard].epoch + MAX_CROSSLINK_EPOCHS),
+        epoch=min(data.target_epoch, state.current_crosslinks[data.shard].epoch + MAX_CROSSLINK_EPOCHS),
        previous_crosslink_root=data.previous_crosslink_root,
        crosslink_data_root=data.crosslink_data_root,
    )
 ```

 ```python
-def get_winning_crosslink_and_attesting_indices(state: BeaconState, shard: Shard, epoch: Epoch) -> Tuple[Crosslink, List[ValidatorIndex]]:
+def get_winning_crosslink_and_attesting_indices(state: BeaconState, epoch: Epoch, shard: Shard) -> Tuple[Crosslink, List[ValidatorIndex]]:
    shard_attestations = [a for a in get_matching_source_attestations(state, epoch) if a.data.shard == shard]
    shard_crosslinks = [get_crosslink_from_attestation_data(state, a.data) for a in shard_attestations]
    candidate_crosslinks = [
@ -1366,7 +1320,7 @@ def get_winning_crosslink_and_attesting_indices(state: BeaconState, shard: Shard
        if hash_tree_root(state.current_crosslinks[shard]) in (c.previous_crosslink_root, hash_tree_root(c))
    ]
    if len(candidate_crosslinks) == 0:
-        return Crosslink(epoch=GENESIS_EPOCH, previous_crosslink_root=ZERO_HASH, crosslink_data_root=ZERO_HASH), []
+        return Crosslink(), []

    def get_attestations_for(crosslink: Crosslink) -> List[PendingAttestation]:
        return [a for a in shard_attestations if get_crosslink_from_attestation_data(state, a.data) == crosslink]
@ -1378,13 +1332,6 @@ def get_winning_crosslink_and_attesting_indices(state: BeaconState, shard: Shard
    return winning_crosslink, get_unslashed_attesting_indices(state, get_attestations_for(winning_crosslink))
 ```

-```python
-def get_earliest_attestation(state: BeaconState, attestations: List[PendingAttestation], index: ValidatorIndex) -> PendingAttestation:
-    return min([
-        a for a in attestations if index in get_attesting_indices(state, a.data, a.aggregation_bitfield)
-    ], key=lambda a: a.inclusion_slot)
-```
-
 #### Justification and finalization

 Run the following function:
@ -1441,12 +1388,11 @@ Run the following function:
 ```python
 def process_crosslinks(state: BeaconState) -> None:
    state.previous_crosslinks = [c for c in state.current_crosslinks]
-    previous_epoch = get_previous_epoch(state)
-    next_epoch = get_current_epoch(state) + 1
-    for slot in range(get_epoch_start_slot(previous_epoch), get_epoch_start_slot(next_epoch)):
-        epoch = slot_to_epoch(slot)
-        for crosslink_committee, shard in get_crosslink_committees_at_slot(state, slot):
-            winning_crosslink, attesting_indices = get_winning_crosslink_and_attesting_indices(state, shard, epoch)
+    for epoch in (get_previous_epoch(state), get_current_epoch(state)):
+        for offset in range(get_epoch_committee_count(state, epoch)):
+            shard = (get_epoch_start_shard(state, epoch) + offset) % SHARD_COUNT
+            crosslink_committee = get_crosslink_committee(state, epoch, shard)
+            winning_crosslink, attesting_indices = get_winning_crosslink_and_attesting_indices(state, epoch, shard)
            if 3 * get_total_balance(state, attesting_indices) >= 2 * get_total_balance(state, crosslink_committee):
                state.current_crosslinks[shard] = winning_crosslink
 ```
@ -1461,15 +1407,14 @@ def get_base_reward(state: BeaconState, index: ValidatorIndex) -> Gwei:
    if adjusted_quotient == 0:
        return 0
    return state.validator_registry[index].effective_balance // adjusted_quotient // BASE_REWARDS_PER_EPOCH
-
 ```

 ```python
 def get_attestation_deltas(state: BeaconState) -> Tuple[List[Gwei], List[Gwei]]:
    previous_epoch = get_previous_epoch(state)
    total_balance = get_total_active_balance(state)
-    rewards = [0 for index in range(len(state.validator_registry))]
-    penalties = [0 for index in range(len(state.validator_registry))]
+    rewards = [0 for _ in range(len(state.validator_registry))]
+    penalties = [0 for _ in range(len(state.validator_registry))]
    eligible_validator_indices = [
        index for index, v in enumerate(state.validator_registry)
        if is_active_validator(v, previous_epoch) or (v.slashed and previous_epoch + 1 < v.withdrawable_epoch)
@ -1490,10 +1435,12 @@ def get_attestation_deltas(state: BeaconState) -> Tuple[List[Gwei], List[Gwei]]:

    # Proposer and inclusion delay micro-rewards
    for index in get_unslashed_attesting_indices(state, matching_source_attestations):
-        earliest_attestation = get_earliest_attestation(state, matching_source_attestations, index)
-        rewards[earliest_attestation.proposer_index] += get_base_reward(state, index) // PROPOSER_REWARD_QUOTIENT
-        inclusion_delay = earliest_attestation.inclusion_slot - earliest_attestation.data.slot
-        rewards[index] += get_base_reward(state, index) * MIN_ATTESTATION_INCLUSION_DELAY // inclusion_delay
+        attestation = min([
+            a for a in matching_source_attestations
+            if index in get_attesting_indices(state, a.data, a.aggregation_bitfield)
+        ], key=lambda a: a.inclusion_delay)
+        rewards[attestation.proposer_index] += get_base_reward(state, index) // PROPOSER_REWARD_QUOTIENT
+        rewards[index] += get_base_reward(state, index) * MIN_ATTESTATION_INCLUSION_DELAY // attestation.inclusion_delay

    # Inactivity penalty
    finality_delay = previous_epoch - state.finalized_epoch
@ -1504,26 +1451,27 @@ def get_attestation_deltas(state: BeaconState) -> Tuple[List[Gwei], List[Gwei]]:
            if index not in matching_target_attesting_indices:
                penalties[index] += state.validator_registry[index].effective_balance * finality_delay // INACTIVITY_PENALTY_QUOTIENT

-    return [rewards, penalties]
+    return rewards, penalties
 ```

 ```python
 def get_crosslink_deltas(state: BeaconState) -> Tuple[List[Gwei], List[Gwei]]:
    rewards = [0 for index in range(len(state.validator_registry))]
    penalties = [0 for index in range(len(state.validator_registry))]
-    for slot in range(get_epoch_start_slot(get_previous_epoch(state)), get_epoch_start_slot(get_current_epoch(state))):
-        epoch = slot_to_epoch(slot)
-        for crosslink_committee, shard in get_crosslink_committees_at_slot(state, slot):
-            winning_crosslink, attesting_indices = get_winning_crosslink_and_attesting_indices(state, shard, epoch)
-            attesting_balance = get_total_balance(state, attesting_indices)
-            committee_balance = get_total_balance(state, crosslink_committee)
-            for index in crosslink_committee:
-                base_reward = get_base_reward(state, index)
-                if index in attesting_indices:
-                    rewards[index] += base_reward * attesting_balance // committee_balance
-                else:
-                    penalties[index] += base_reward
-    return [rewards, penalties]
+    epoch = get_previous_epoch(state)
+    for offset in range(get_epoch_committee_count(state, epoch)):
+        shard = (get_epoch_start_shard(state, epoch) + offset) % SHARD_COUNT
+        crosslink_committee = get_crosslink_committee(state, epoch, shard)
+        winning_crosslink, attesting_indices = get_winning_crosslink_and_attesting_indices(state, epoch, shard)
+        attesting_balance = get_total_balance(state, attesting_indices)
+        committee_balance = get_total_balance(state, crosslink_committee)
+        for index in crosslink_committee:
+            base_reward = get_base_reward(state, index)
+            if index in attesting_indices:
+                rewards[index] += base_reward * attesting_balance // committee_balance
+            else:
+                penalties[index] += base_reward
+    return rewards, penalties
 ```

 Run the following function:
@ -1562,6 +1510,7 @@ def process_registry_updates(state: BeaconState) -> None:
    ], key=lambda index: state.validator_registry[index].activation_eligibility_epoch)
    # Dequeued validators for activation up to churn limit (without resetting activation epoch)
    for index in activation_queue[:get_churn_limit(state)]:
+        validator = state.validator_registry[index]
        if validator.activation_epoch == FAR_FUTURE_EPOCH:
            validator.activation_epoch = get_delayed_activation_exit_epoch(get_current_epoch(state))
 ```
@ -1603,10 +1552,10 @@ def process_final_updates(state: BeaconState) -> None:
        state.eth1_data_votes = []
    # Update effective balances with hysteresis
    for index, validator in enumerate(state.validator_registry):
-        balance = min(state.balances[index], MAX_EFFECTIVE_BALANCE)
+        balance = state.balances[index]
        HALF_INCREMENT = EFFECTIVE_BALANCE_INCREMENT // 2
        if balance < validator.effective_balance or validator.effective_balance + 3 * HALF_INCREMENT < balance:
-            validator.effective_balance = balance - balance % EFFECTIVE_BALANCE_INCREMENT
+            validator.effective_balance = min(balance - balance % EFFECTIVE_BALANCE_INCREMENT, MAX_EFFECTIVE_BALANCE)
    # Update start shard
    state.latest_start_shard = (state.latest_start_shard + get_shard_delta(state, current_epoch)) % SHARD_COUNT
    # Set active index root
@ -1691,6 +1640,8 @@ def process_eth1_data(state: BeaconState, block: BeaconBlock) -> None:

 #### Operations

+*Note*: All functions in this section mutate `state`.
+
 ##### Proposer slashings

 Verify that `len(block.body.proposer_slashings) <= MAX_PROPOSER_SLASHINGS`.
@ -1702,7 +1653,6 @@ def process_proposer_slashing(state: BeaconState,
                              proposer_slashing: ProposerSlashing) -> None:
    """
    Process ``ProposerSlashing`` operation.
-    Note that this function mutates ``state``.
    """
    proposer = state.validator_registry[proposer_slashing.proposer_index]
    # Verify that the epoch is the same
@ -1730,31 +1680,21 @@ def process_attester_slashing(state: BeaconState,
                              attester_slashing: AttesterSlashing) -> None:
    """
    Process ``AttesterSlashing`` operation.
-    Note that this function mutates ``state``.
    """
-    attestation1 = attester_slashing.attestation_1
-    attestation2 = attester_slashing.attestation_2
-    # Check that the attestations are conflicting
-    assert attestation1.data != attestation2.data
-    assert (
-        is_double_vote(attestation1.data, attestation2.data) or
-        is_surround_vote(attestation1.data, attestation2.data)
-    )
+    attestation_1 = attester_slashing.attestation_1
+    attestation_2 = attester_slashing.attestation_2
+    assert is_slashable_attestation_data(attestation_1.data, attestation_2.data)
+    assert verify_indexed_attestation(state, attestation_1)
+    assert verify_indexed_attestation(state, attestation_2)

-    assert verify_indexed_attestation(state, attestation1)
-    assert verify_indexed_attestation(state, attestation2)
-    attesting_indices_1 = attestation1.custody_bit_0_indices + attestation1.custody_bit_1_indices
-    attesting_indices_2 = attestation2.custody_bit_0_indices + attestation2.custody_bit_1_indices
-    slashable_indices = [
-        index for index in attesting_indices_1
-        if (
-            index in attesting_indices_2 and
-            is_slashable_validator(state.validator_registry[index], get_current_epoch(state))
-        )
-    ]
-    assert len(slashable_indices) >= 1
-    for index in slashable_indices:
-        slash_validator(state, index)
+    slashed_any = False
+    attesting_indices_1 = attestation_1.custody_bit_0_indices + attestation_1.custody_bit_1_indices
+    attesting_indices_2 = attestation_2.custody_bit_0_indices + attestation_2.custody_bit_1_indices
+    for index in set(attesting_indices_1).intersection(attesting_indices_2):
+        if is_slashable_validator(state.validator_registry[index], get_current_epoch(state)):
+            slash_validator(state, index)
+            slashed_any = True
+    assert slashed_any
 ```

 ##### Attestations
@ -1767,15 +1707,13 @@ For each `attestation` in `block.body.attestations`, run the following function:
 def process_attestation(state: BeaconState, attestation: Attestation) -> None:
    """
    Process ``Attestation`` operation.
-    Note that this function mutates ``state``.
    """
    data = attestation.data
-    min_slot = state.slot - SLOTS_PER_EPOCH if get_current_epoch(state) > GENESIS_EPOCH else GENESIS_SLOT
-    assert min_slot <= data.slot <= state.slot - MIN_ATTESTATION_INCLUSION_DELAY
+    attestation_slot = get_attestation_data_slot(state, data)
+    assert attestation_slot + MIN_ATTESTATION_INCLUSION_DELAY <= state.slot <= attestation_slot + SLOTS_PER_EPOCH

    # Check target epoch, source epoch, source root, and source crosslink
-    target_epoch = slot_to_epoch(data.slot)
-    assert (target_epoch, data.source_epoch, data.source_root, data.previous_crosslink_root) in {
+    assert (data.target_epoch, data.source_epoch, data.source_root, data.previous_crosslink_root) in {
        (get_current_epoch(state), state.current_justified_epoch, state.current_justified_root, hash_tree_root(state.current_crosslinks[data.shard])),
        (get_previous_epoch(state), state.previous_justified_epoch, state.previous_justified_root, hash_tree_root(state.previous_crosslinks[data.shard])),
    }
@ -1790,10 +1728,10 @@ def process_attestation(state: BeaconState, attestation: Attestation) -> None:
    pending_attestation = PendingAttestation(
        data=data,
        aggregation_bitfield=attestation.aggregation_bitfield,
-        inclusion_slot=state.slot,
+        inclusion_delay=state.slot - attestation_slot,
        proposer_index=get_beacon_proposer_index(state),
    )
-    if target_epoch == get_current_epoch(state):
+    if data.target_epoch == get_current_epoch(state):
        state.current_epoch_attestations.append(pending_attestation)
    else:
        state.previous_epoch_attestations.append(pending_attestation)
@ -1809,7 +1747,6 @@ For each `deposit` in `block.body.deposits`, run the following function:
 def process_deposit(state: BeaconState, deposit: Deposit) -> None:
    """
    Process an Eth1 deposit, registering a validator or increasing its balance.
-    Note that this function mutates ``state``.
    """
    # Verify the Merkle branch
    assert verify_merkle_branch(
@ -1840,7 +1777,7 @@ def process_deposit(state: BeaconState, deposit: Deposit) -> None:
            activation_epoch=FAR_FUTURE_EPOCH,
            exit_epoch=FAR_FUTURE_EPOCH,
            withdrawable_epoch=FAR_FUTURE_EPOCH,
-            effective_balance=amount - amount % EFFECTIVE_BALANCE_INCREMENT
+            effective_balance=min(amount - amount % EFFECTIVE_BALANCE_INCREMENT, MAX_EFFECTIVE_BALANCE)
        ))
        state.balances.append(amount)
    else:
@ -1859,7 +1796,6 @@ For each `exit` in `block.body.voluntary_exits`, run the following function:
 def process_voluntary_exit(state: BeaconState, exit: VoluntaryExit) -> None:
    """
    Process ``VoluntaryExit`` operation.
-    Note that this function mutates ``state``.
    """
    validator = state.validator_registry[exit.validator_index]
    # Verify the validator is active
@ -1869,7 +1805,7 @@ def process_voluntary_exit(state: BeaconState, exit: VoluntaryExit) -> None:
    # Exits must specify an epoch when they become valid; they are not valid before then
    assert get_current_epoch(state) >= exit.epoch
    # Verify the validator has been active long enough
-    assert get_current_epoch(state) - validator.activation_epoch >= PERSISTENT_COMMITTEE_PERIOD
+    assert get_current_epoch(state) >= validator.activation_epoch + PERSISTENT_COMMITTEE_PERIOD
    # Verify signature
    domain = get_domain(state, DOMAIN_VOLUNTARY_EXIT, exit.epoch)
    assert bls_verify(validator.pubkey, signing_root(exit), exit.signature, domain)
@ -1887,7 +1823,6 @@ For each `transfer` in `block.body.transfers`, run the following function:
 def process_transfer(state: BeaconState, transfer: Transfer) -> None:
    """
    Process ``Transfer`` operation.
-    Note that this function mutates ``state``.
    """
    # Verify the amount and fee are not individually too big (for anti-overflow purposes)
    assert state.balances[transfer.sender] >= max(transfer.amount, transfer.fee)
--- a/specs/core/0_deposit-contract.md
+++ b/specs/core/0_deposit-contract.md
@ -1,6 +1,6 @@
 # Ethereum 2.0 Phase 0 -- Deposit Contract

-**NOTICE**: This document is a work in progress for researchers and implementers.
+**Notice**: This document is a work-in-progress for researchers and implementers.

 ## Table of contents
 <!-- TOC -->
@ -9,53 +9,70 @@
    - [Table of contents](#table-of-contents)
    - [Introduction](#introduction)
    - [Constants](#constants)
-        - [Deposit contract](#time-parameters)
+        - [Gwei values](#gwei-values)
+        - [Contract](#contract)
    - [Ethereum 1.0 deposit contract](#ethereum-10-deposit-contract)
-        - [Deposit arguments](#deposit-arguments)
-        - [Withdrawal credentials](#withdrawal-credentials)
+        - [Arguments](#arguments)
+            - [Withdrawal credentials](#withdrawal-credentials)
+            - [Amount](#amount)
+    - [Event logs](#event-logs)
        - [`Deposit` logs](#deposit-logs)
        - [`Eth2Genesis` log](#eth2genesis-log)
-        - [Vyper code](#vyper-code)
+    - [Vyper code](#vyper-code)

 <!-- /TOC -->

 ## Introduction

-This document represents is the specification for the beacon chain deposit contract, part of Ethereum 2.0 phase 0.
+This document represents the specification for the beacon chain deposit contract, part of Ethereum 2.0 Phase 0.

 ## Constants

-### Deposit contract
+### Gwei values
+
+| Name | Value | Unit |
+| - | - | - |
+| `FULL_DEPOSIT_AMOUNT` | `32 * 10**9` | Gwei |
+
+### Contract

 | Name | Value |
 | - | - |
 | `DEPOSIT_CONTRACT_ADDRESS` | **TBD** |
 | `DEPOSIT_CONTRACT_TREE_DEPTH` | `2**5` (= 32) |
+| `CHAIN_START_FULL_DEPOSIT_THRESHOLD` | `2**16` (= 65,536) |

 ## Ethereum 1.0 deposit contract

-The initial deployment phases of Ethereum 2.0 are implemented without consensus changes to Ethereum 1.0. A deposit contract at address `DEPOSIT_CONTRACT_ADDRESS` is added to Ethereum 1.0 for deposits of ETH to the beacon chain. Validator balances will be withdrawable to the shards in phase 2, i.e. when the EVM2.0 is deployed and the shards have state.
+The initial deployment phases of Ethereum 2.0 are implemented without consensus changes to Ethereum 1.0. A deposit contract at address `DEPOSIT_CONTRACT_ADDRESS` is added to Ethereum 1.0 for deposits of ETH to the beacon chain. Validator balances will be withdrawable to the shards in Phase 2 (i.e. when the EVM 2.0 is deployed and the shards have state).

-### Deposit arguments
+### Arguments

-The deposit contract has a single `deposit` function which takes as argument a SimpleSerialize'd `DepositData`.
+The deposit contract has a `deposit` function which takes the amount in Ethereum 1.0 transaction, and arguments `pubkey: bytes[48], withdrawal_credentials: bytes[32], signature: bytes[96]` corresponding to `DepositData`.

-### Withdrawal credentials
+#### Withdrawal credentials

-One of the `DepositData` fields is `withdrawal_credentials`. It is a commitment to credentials for withdrawals to shards. The first byte of `withdrawal_credentials` is a version number. As of now the only expected format is as follows:
+One of the `DepositData` fields is `withdrawal_credentials`. It is a commitment to credentials for withdrawals to shards. The first byte of `withdrawal_credentials` is a version number. As of now, the only expected format is as follows:

 * `withdrawal_credentials[:1] == BLS_WITHDRAWAL_PREFIX_BYTE`
 * `withdrawal_credentials[1:] == hash(withdrawal_pubkey)[1:]` where `withdrawal_pubkey` is a BLS pubkey

 The private key corresponding to `withdrawal_pubkey` will be required to initiate a withdrawal. It can be stored separately until a withdrawal is required, e.g. in cold storage.

+#### Amount
+
+* A valid deposit amount should be at least `MIN_DEPOSIT_AMOUNT` in Gwei.
+* A deposit with an amount greater than or equal to `FULL_DEPOSIT_AMOUNT` in Gwei is considered as a full deposit.
+
+## Event logs
+
 ### `Deposit` logs

-Every Ethereum 1.0 deposit, of size between `MIN_DEPOSIT_AMOUNT` and `MAX_DEPOSIT_AMOUNT`, emits a `Deposit` log for consumption by the beacon chain. The deposit contract does little validation, pushing most of the validator onboarding logic to the beacon chain. In particular, the proof of possession (a BLS12 signature) is not verified by the deposit contract.
+Every Ethereum 1.0 deposit, of size at least `MIN_DEPOSIT_AMOUNT`, emits a `Deposit` log for consumption by the beacon chain. The deposit contract does little validation, pushing most of the validator onboarding logic to the beacon chain. In particular, the proof of possession (a BLS12-381 signature) is not verified by the deposit contract.

 ### `Eth2Genesis` log

-When a sufficient amount of full deposits have been made, the deposit contract emits the `Eth2Genesis` log. The beacon chain state may then be initialized by calling the `get_genesis_beacon_state` function (defined below) where:
+When `CHAIN_START_FULL_DEPOSIT_THRESHOLD` of full deposits have been made, the deposit contract emits the `Eth2Genesis` log. The beacon chain state may then be initialized by calling the `get_genesis_beacon_state` function (defined below) where:

 * `genesis_time` equals `time` in the `Eth2Genesis` log
 * `latest_eth1_data.deposit_root` equals `deposit_root` in the `Eth2Genesis` log
@ -63,14 +80,14 @@ When a sufficient amount of full deposits have been made, the deposit contract e
 * `latest_eth1_data.block_hash` equals the hash of the block that included the log
 * `genesis_validator_deposits` is a list of `Deposit` objects built according to the `Deposit` logs up to the deposit that triggered the `Eth2Genesis` log, processed in the order in which they were emitted (oldest to newest)

-### Vyper code
+## Vyper code

 The source for the Vyper contract lives in a [separate repository](https://github.com/ethereum/deposit_contract) at [https://github.com/ethereum/deposit_contract/blob/master/deposit_contract/contracts/validator_registration.v.py](https://github.com/ethereum/deposit_contract/blob/master/deposit_contract/contracts/validator_registration.v.py).

-Note: to save ~10x on gas this contract uses a somewhat unintuitive progressive Merkle root calculation algo that requires only O(log(n)) storage. See https://github.com/ethereum/research/blob/master/beacon_chain_impl/progressive_merkle_tree.py for an implementation of the same algo in python tested for correctness.
+*Note*: To save ~10x on gas, this contract uses a somewhat unintuitive progressive Merkle root calculation algo that requires only O(log(n)) storage. See https://github.com/ethereum/research/blob/master/beacon_chain_impl/progressive_merkle_tree.py for an implementation of the same algo in Python tested for correctness.

 For convenience, we provide the interface to the contract here:

 * `__init__()`: initializes the contract
 * `get_deposit_root() -> bytes32`: returns the current root of the deposit tree
-* `deposit(bytes[512])`: adds a deposit instance to the deposit tree, incorporating the input argument and the value transferred in the given call. Note: the amount of value transferred *must* be within `MIN_DEPOSIT_AMOUNT` and `MAX_DEPOSIT_AMOUNT`, inclusive. Each of these constants are specified in units of Gwei.
+* `deposit(pubkey: bytes[48], withdrawal_credentials: bytes[32], signature: bytes[96])`: adds a deposit instance to the deposit tree, incorporating the input arguments and the value transferred in the given call. *Note*: The amount of value transferred *must* be at least `MIN_DEPOSIT_AMOUNT`. Each of these constants are specified in units of Gwei.
--- a/specs/core/0_fork-choice.md
+++ b/specs/core/0_fork-choice.md
@ -1,6 +1,6 @@
 # Ethereum 2.0 Phase 0 -- Beacon Chain Fork Choice

-**NOTICE**: This document is a work in progress for researchers and implementers.
+**Notice**: This document is a work-in-progress for researchers and implementers.

 ## Table of contents
 <!-- TOC -->
@ -13,12 +13,14 @@
        - [Time parameters](#time-parameters)
    - [Beacon chain processing](#beacon-chain-processing)
        - [Beacon chain fork choice rule](#beacon-chain-fork-choice-rule)
+    - [Implementation notes](#implementation-notes)
+        - [Justification and finality at genesis](#justification-and-finality-at-genesis)

 <!-- /TOC -->

 ## Introduction

-This document represents is the specification for the beacon chain fork choice rule, part of Ethereum 2.0 phase 0.
+This document represents the specification for the beacon chain fork choice rule, part of Ethereum 2.0 Phase 0.

 ## Prerequisites

@ -40,17 +42,17 @@ Processing the beacon chain is similar to processing the Ethereum 1.0 chain. Cli
 * An Ethereum 1.0 block pointed to by the `state.latest_eth1_data.block_hash` has been processed and accepted.
 * The node's Unix time is greater than or equal to `state.genesis_time + block.slot * SECONDS_PER_SLOT`.

-Note: Leap seconds mean that slots will occasionally last `SECONDS_PER_SLOT + 1` or `SECONDS_PER_SLOT - 1` seconds, possibly several times a year.
+*Note*: Leap seconds mean that slots will occasionally last `SECONDS_PER_SLOT + 1` or `SECONDS_PER_SLOT - 1` seconds, possibly several times a year.

-Note: Nodes needs to have a clock that is roughly (i.e. within `SECONDS_PER_SLOT` seconds) synchronized with the other nodes.
+*Note*: Nodes needs to have a clock that is roughly (i.e. within `SECONDS_PER_SLOT` seconds) synchronized with the other nodes.

 ### Beacon chain fork choice rule

-The beacon chain fork choice rule is a hybrid that combines justification and finality with Latest Message Driven (LMD) Greediest Heaviest Observed SubTree (GHOST). At any point in time a [validator](#dfn-validator) `v` subjectively calculates the beacon chain head as follows.
+The beacon chain fork choice rule is a hybrid that combines justification and finality with Latest Message Driven (LMD) Greediest Heaviest Observed SubTree (GHOST). At any point in time, a validator `v` subjectively calculates the beacon chain head as follows.

-* Abstractly define `Store` as the type of storage object for the chain data and `store` be the set of attestations and blocks that the [validator](#dfn-validator) `v` has observed and verified (in particular, block ancestors must be recursively verified). Attestations not yet included in any chain are still included in `store`.
-* Let `finalized_head` be the finalized block with the highest epoch. (A block `B` is finalized if there is a descendant of `B` in `store` the processing of which sets `B` as finalized.)
-* Let `justified_head` be the descendant of `finalized_head` with the highest epoch that has been justified for at least 1 epoch. (A block `B` is justified if there is a descendant of `B` in `store` the processing of which sets `B` as justified.) If no such descendant exists set `justified_head` to `finalized_head`.
+* Abstractly define `Store` as the type of storage object for the chain data, and let `store` be the set of attestations and blocks that the validator `v` has observed and verified (in particular, block ancestors must be recursively verified). Attestations not yet included in any chain are still included in `store`.
+* Let `finalized_head` be the finalized block with the highest epoch. (A block `B` is finalized if there is a descendant of `B` in `store`, the processing of which sets `B` as finalized.)
+* Let `justified_head` be the descendant of `finalized_head` with the highest epoch that has been justified for at least 1 epoch. (A block `B` is justified if there is a descendant of `B` in `store` the processing of which sets `B` as justified.) If no such descendant exists, set `justified_head` to `finalized_head`.
 * Let `get_ancestor(store: Store, block: BeaconBlock, slot: Slot) -> BeaconBlock` be the ancestor of `block` with slot number `slot`. The `get_ancestor` function can be defined recursively as:

 ```python
@ -66,9 +68,9 @@ def get_ancestor(store: Store, block: BeaconBlock, slot: Slot) -> BeaconBlock:
        return get_ancestor(store, store.get_parent(block), slot)
 ```

-* Let `get_latest_attestation(store: Store, index: ValidatorIndex) -> Attestation` be the attestation with the highest slot number in `store` from the validator with the given `index`. If several such attestations exist, use the one the [validator](#dfn-validator) `v` observed first.
+* Let `get_latest_attestation(store: Store, index: ValidatorIndex) -> Attestation` be the attestation with the highest slot number in `store` from the validator with the given `index`. If several such attestations exist, use the one the validator `v` observed first.
 * Let `get_latest_attestation_target(store: Store, index: ValidatorIndex) -> BeaconBlock` be the target block in the attestation `get_latest_attestation(store, index)`.
-* Let `get_children(store: Store, block: BeaconBlock) -> List[BeaconBlock]` returns the child blocks of the given `block`.
+* Let `get_children(store: Store, block: BeaconBlock) -> List[BeaconBlock]` return the child blocks of the given `block`.
 * Let `justified_head_state` be the resulting `BeaconState` object from processing the chain up to the `justified_head`.
 * The `head` is `lmd_ghost(store, justified_head_state, justified_head)` where the function `lmd_ghost` is defined below. Note that the implementation below is suboptimal; there are implementations that compute the head in time logarithmic in slot count.

@ -99,3 +101,9 @@ def lmd_ghost(store: Store, start_state: BeaconState, start_block: BeaconBlock)
        # Ties broken by favoring block with lexicographically higher root
        head = max(children, key=lambda x: (get_vote_count(x), hash_tree_root(x)))
 ```
+
+## Implementation notes
+
+### Justification and finality at genesis
+
+During genesis, justification and finality root fields within the `BeaconState` reference `ZERO_HASH` rather than a known block. `ZERO_HASH` in `previous_justified_root`, `current_justified_root`, and `finalized_root` should be considered as an alias to the root of the genesis block.
--- a/specs/core/1_custody-game.md
+++ b/specs/core/1_custody-game.md
@ -1,6 +1,6 @@
 # Ethereum 2.0 Phase 1 -- Custody Game

-**NOTICE**: This spec is a work-in-progress for researchers and implementers.
+**Notice**: This document is a work-in-progress for researchers and implementers.

 ## Table of contents

@ -14,6 +14,7 @@
        - [Misc](#misc)
        - [Time parameters](#time-parameters)
        - [Max operations per block](#max-operations-per-block)
+        - [Reward and penalty quotients](#reward-and-penalty-quotients)
        - [Signature domains](#signature-domains)
    - [Data structures](#data-structures)
        - [Custody objects](#custody-objects)
@ -22,7 +23,9 @@
            - [`CustodyChunkChallengeRecord`](#custodychunkchallengerecord)
            - [`CustodyBitChallengeRecord`](#custodybitchallengerecord)
            - [`CustodyResponse`](#custodyresponse)
+        - [New beacon operations](#new-beacon-operations)
            - [`CustodyKeyReveal`](#custodykeyreveal)
+            - [`EarlyDerivedSecretReveal`](#earlyderivedsecretreveal)
        - [Phase 0 container updates](#phase-0-container-updates)
            - [`Validator`](#validator)
            - [`BeaconState`](#beaconstate)
@ -32,37 +35,40 @@
        - [`empty`](#empty)
        - [`get_crosslink_chunk_count`](#get_crosslink_chunk_count)
        - [`get_custody_chunk_bit`](#get_custody_chunk_bit)
-        - [`epoch_to_custody_period`](#epoch_to_custody_period)
+        - [`get_randao_epoch_for_custody_period`](#get_randao_epoch_for_custody_period)
+        - [`get_validators_custody_reveal_period`](#get_validators_custody_reveal_period)
+        - [`get_chunk_bits_root`](#get_chunk_bits_root)
        - [`replace_empty_or_append`](#replace_empty_or_append)
-        - [`verify_custody_key`](#verify_custody_key)
    - [Per-block processing](#per-block-processing)
        - [Operations](#operations)
-            - [Custody reveals](#custody-reveals)
+            - [Custody key reveals](#custody-key-reveals)
+            - [Early derived secret reveals](#early-derived-secret-reveals)
            - [Chunk challenges](#chunk-challenges)
            - [Bit challenges](#bit-challenges)
            - [Custody responses](#custody-responses)
    - [Per-epoch processing](#per-epoch-processing)
+        - [Handling of custody-related deadlines](#handling-of-custody-related-deadlines)

 <!-- /TOC -->

 ## Introduction

-This document details the beacon chain additions and changes in Phase 1 of Ethereum 2.0 to support the shard data custody game, building upon the [phase 0](0_beacon-chain.md) specification.
+This document details the beacon chain additions and changes in Phase 1 of Ethereum 2.0 to support the shard data custody game, building upon the [Phase 0](0_beacon-chain.md) specification.

 ## Terminology

-* **Custody game**:
-* **Custody period**:
-* **Custody chunk**:
-* **Custody chunk bit**:
-* **Custody chunk challenge**:
-* **Custody bit**:
-* **Custody bit challenge**:
-* **Custody key**:
-* **Custody key reveal**:
-* **Custody key mask**:
-* **Custody response**:
-* **Custody response deadline**:
+* **Custody game**—
+* **Custody period**—
+* **Custody chunk**—
+* **Custody chunk bit**—
+* **Custody chunk challenge**—
+* **Custody bit**—
+* **Custody bit challenge**—
+* **Custody key**—
+* **Custody key reveal**—
+* **Custody key mask**—
+* **Custody response**—
+* **Custody response deadline**—

 ## Constants

@ -79,24 +85,32 @@ This document details the beacon chain additions and changes in Phase 1 of Ether
 | Name | Value | Unit | Duration |
 | - | - | :-: | :-: |
 | `MAX_CHUNK_CHALLENGE_DELAY` | `2**11` (= 2,048) | epochs | ~9 days |
-| `EPOCHS_PER_CUSTODY_PERIOD` | `2**11` (= 2,048) | epochs | ~9 days |
 | `CUSTODY_RESPONSE_DEADLINE` | `2**14` (= 16,384) | epochs | ~73 days |
+| `RANDAO_PENALTY_EPOCHS` | `2**1` (= 2) | epochs | 12.8 minutes |
+| `EARLY_DERIVED_SECRET_PENALTY_MAX_FUTURE_EPOCHS` | `2**14` | epochs | ~73 days |
+| `EPOCHS_PER_CUSTODY_PERIOD` | `2**11` (= 2,048) | epochs | ~9 days |
+| `CUSTODY_PERIOD_TO_RANDAO_PADDING` | `2**11` (= 2,048) | epochs | ~9 days |
+| `MAX_REVEAL_LATENESS_DECREMENT` | `2**7` (= 128) | epochs | ~14 hours |

 ### Max operations per block

 | Name | Value |
 | - | - |
 | `MAX_CUSTODY_KEY_REVEALS` | `2**4` (= 16) |
+| `MAX_EARLY_DERIVED_SECRET_REVEALS` | `1` |
 | `MAX_CUSTODY_CHUNK_CHALLENGES` | `2**2` (= 4) |
 | `MAX_CUSTODY_BIT_CHALLENGES` | `2**2` (= 4) |
 | `MAX_CUSTODY_RESPONSES` | `2**5` (= 32) |

+### Reward and penalty quotients
+
+| `EARLY_DERIVED_SECRET_REVEAL_SLOT_REWARD_MULTIPLE` | `2**1` (= 2) |
+
 ### Signature domains

 | Name | Value |
 | - | - |
-| `DOMAIN_CUSTODY_KEY_REVEAL` | `6` |
-| `DOMAIN_CUSTODY_BIT_CHALLENGE` | `7` |
+| `DOMAIN_CUSTODY_BIT_CHALLENGE` | `6` |

 ## Data structures

@ -148,7 +162,8 @@ This document details the beacon chain additions and changes in Phase 1 of Ether
    'responder_index': ValidatorIndex,
    'deadline': Epoch,
    'crosslink_data_root': Hash,
-    'chunk_bits': Bitfield,
+    'chunk_count': 'uint64',
+    'chunk_bits_merkle_root': Hash,
    'responder_key': BLSSignature,
 }
 ```
@ -160,19 +175,41 @@ This document details the beacon chain additions and changes in Phase 1 of Ether
    'challenge_index': 'uint64',
    'chunk_index': 'uint64',
    'chunk': ['byte', BYTES_PER_CUSTODY_CHUNK],
-    'branch': [Hash],
+    'data_branch': [Hash],
+    'chunk_bits_branch': [Hash],
+    'chunk_bits_leaf': Hash,
 }
 ```

+### New beacon operations
+
 #### `CustodyKeyReveal`

 ```python
 {
-    'revealer_index': ValidatorIndex,
-    'period': 'uint64',
-    'key': BLSSignature,
-    'masker_index': ValidatorIndex,
-    'mask': Hash,
+    # Index of the validator whose key is being revealed
+    'revealer_index': 'uint64',
+    # Reveal (masked signature)
+    'reveal': 'bytes96',
+}
+```
+
+#### `EarlyDerivedSecretReveal`
+
+Represents an early (punishable) reveal of one of the derived secrets, where derived secrets are RANDAO reveals and custody reveals (both are part of the same domain).
+
+```python
+{
+    # Index of the validator whose key is being revealed
+    'revealed_index': 'uint64',
+    # RANDAO epoch of the key that is being revealed
+    'epoch': 'uint64',
+    # Reveal (masked signature)
+    'reveal': 'bytes96',
+    # Index of the validator who revealed (whistleblower)
+    'masker_index': 'uint64',
+    # Mask used to hide the actual reveal signature (prevent reveal from being stolen)
+    'mask': 'bytes32',
 }
 ```

@ -183,7 +220,10 @@ Add the following fields to the end of the specified container objects. Fields w
 #### `Validator`

 ```python
-    'custody_reveal_index': 'uint64',
+    # next_custody_reveal_period is initialized to the custody period
+    # (of the particular validator) in which the validator is activated
+    # = get_validators_custody_reveal_period(...)
+    'next_custody_reveal_period': 'uint64',
    'max_reveal_lateness': 'uint64',
 ```

@ -193,15 +233,20 @@ Add the following fields to the end of the specified container objects. Fields w
    'custody_chunk_challenge_records': [CustodyChunkChallengeRecord],
    'custody_bit_challenge_records': [CustodyBitChallengeRecord],
    'custody_challenge_index': 'uint64',
+
+    # Future derived secrets already exposed; contains the indices of the exposed validator
+    # at RANDAO reveal period % EARLY_DERIVED_SECRET_PENALTY_MAX_FUTURE_EPOCHS
+    'exposed_derived_secrets': [['uint64'], EARLY_DERIVED_SECRET_PENALTY_MAX_FUTURE_EPOCHS],
 ```

 #### `BeaconBlockBody`

 ```python
-    'custody_key_reveals': [CustodyKeyReveal],
    'custody_chunk_challenges': [CustodyChunkChallenge],
    'custody_bit_challenges': [CustodyBitChallenge],
    'custody_responses': [CustodyResponse],
+    'custody_key_reveals': [CustodyKeyReveal],
+    'early_derived_secret_reveals': [EarlyDerivedSecretReveal],
 ```

 ## Helpers
@ -233,15 +278,44 @@ def get_custody_chunk_bit(key: BLSSignature, chunk: bytes) -> bool:
    return get_bitfield_bit(hash(challenge.responder_key + chunk), 0)
 ```

-### `epoch_to_custody_period`
+### `get_chunk_bits_root`

 ```python
-def epoch_to_custody_period(epoch: Epoch) -> int:
-    return epoch // EPOCHS_PER_CUSTODY_PERIOD
+def get_chunk_bits_root(chunk_bitfield: Bitfield) -> Bytes32:
+    aggregated_bits = bytearray([0] * 32)
+    for i in range(0, len(chunk_bitfield), 32):
+        for j in range(32):
+            aggregated_bits[j] ^= chunk_bitfield[i+j]
+    return hash(aggregated_bits)
+```
+
+### `get_randao_epoch_for_custody_period`
+
+```python
+def get_randao_epoch_for_custody_period(period: int, validator_index: ValidatorIndex) -> Epoch:
+    next_period_start = (period + 1) * EPOCHS_PER_CUSTODY_PERIOD - validator_index % EPOCHS_PER_CUSTODY_PERIOD
+    return next_period_start + CUSTODY_PERIOD_TO_RANDAO_PADDING
+```
+
+### `get_validators_custody_reveal_period`
+
+ ```python
+def get_validators_custody_reveal_period(state: BeaconState,
+                                         validator_index: ValidatorIndex,
+                                         epoch: Epoch=None) -> int:
+    '''
+    This function returns the reveal period for a given validator.
+    If no epoch is supplied, the current epoch is assumed.
+    Note: This function implicitly requires that validators are not removed from the
+    validator set in fewer than EPOCHS_PER_CUSTODY_PERIOD epochs
+    '''
+    epoch = get_current_epoch(state) if epoch is None else epoch
+    return (epoch + validator_index % EPOCHS_PER_CUSTODY_PERIOD) // EPOCHS_PER_CUSTODY_PERIOD
 ```

 ### `replace_empty_or_append`

+
 ```python
 def replace_empty_or_append(list: List[Any], new_element: Any) -> int:
    for i in range(len(list)):
@ -252,68 +326,131 @@ def replace_empty_or_append(list: List[Any], new_element: Any) -> int:
    return len(list) - 1
 ```

-### `verify_custody_key`
-
-```python
-def verify_custody_key(state: BeaconState, reveal: CustodyKeyReveal) -> bool:
-    # Case 1: non-masked non-punitive non-early reveal
-    pubkeys = [state.validator_registry[reveal.revealer_index].pubkey]
-    message_hashes = [hash_tree_root(reveal.period)]
-
-    # Case 2: masked punitive early reveal
-    # Masking prevents proposer stealing the whistleblower reward
-    # Secure under the aggregate extraction infeasibility assumption
-    # See pages 11-12 of https://crypto.stanford.edu/~dabo/pubs/papers/aggreg.pdf
-    if reveal.mask != ZERO_HASH:
-        pubkeys.append(state.validator_registry[reveal.masker_index].pubkey)
-        message_hashes.append(reveal.mask)
-
-    return bls_verify_multiple(
-        pubkeys=pubkeys,
-        message_hashes=message_hashes,
-        signature=reveal.key,
-        domain=get_domain(
-            fork=state.fork,
-            epoch=reveal.period * EPOCHS_PER_CUSTODY_PERIOD,
-            domain_type=DOMAIN_CUSTODY_KEY_REVEAL,
-        ),
-    )
-```
-
 ## Per-block processing

 ### Operations

-Add the following operations to the per-block processing, in order the given below and after all other operations in phase 0.
+Add the following operations to the per-block processing, in the order given below and after all other operations in Phase 0.

-#### Custody reveals
+#### Custody key reveals

 Verify that `len(block.body.custody_key_reveals) <= MAX_CUSTODY_KEY_REVEALS`.

 For each `reveal` in `block.body.custody_key_reveals`, run the following function:

 ```python
-def process_custody_reveal(state: BeaconState,
+def process_custody_key_reveal(state: BeaconState,
                           reveal: CustodyKeyReveal) -> None:
-    assert verify_custody_key(state, reveal)
+
+    """
+    Process ``CustodyKeyReveal`` operation.
+    Note that this function mutates ``state``.
+    """
+
    revealer = state.validator_registry[reveal.revealer_index]
-    current_custody_period = epoch_to_custody_period(get_current_epoch(state))
+    epoch_to_sign = get_randao_epoch_for_custody_period(revealer.next_custody_reveal_period, reveal.revealed_index)

-    # Case 1: non-masked non-punitive non-early reveal
-    if reveal.mask == ZERO_HASH:
-        assert reveal.period == epoch_to_custody_period(revealer.activation_epoch) + revealer.custody_reveal_index
-        # Revealer is active or exited
-        assert is_active_validator(revealer, get_current_epoch(state)) or revealer.exit_epoch > get_current_epoch(state)
-        revealer.custody_reveal_index += 1
-        revealer.max_reveal_lateness = max(revealer.max_reveal_lateness, current_custody_period - reveal.period)
-        proposer_index = get_beacon_proposer_index(state)
-        increase_balance(state, proposer_index, base_reward(state, index) // MINOR_REWARD_QUOTIENT)
+    assert revealer.next_custody_reveal_period < get_validators_custody_reveal_period(state, reveal.revealed_index)

-    # Case 2: masked punitive early reveal
+    # Revealed validator is active or exited, but not withdrawn
+    assert is_slashable_validator(revealer, get_current_epoch(state))
+
+    # Verify signature
+    assert bls_verify(
+        pubkey=revealer.pubkey,
+        message_hash=hash_tree_root(epoch_to_sign),
+        signature=reveal.reveal,
+        domain=get_domain(
+            state=state,
+            domain_type=DOMAIN_RANDAO,
+            message_epoch=epoch_to_sign,
+        ),
+    )
+
+    # Decrement max reveal lateness if response is timely
+    if revealer.next_custody_reveal_period == get_validators_custody_reveal_period(state, reveal.revealer_index) - 2:
+            revealer.max_reveal_lateness -=  MAX_REVEAL_LATENESS_DECREMENT
+    revealer.max_reveal_lateness = max(revealed_validator.max_reveal_lateness, get_validators_custody_reveal_period(state, reveal.revealed_index) - revealer.next_custody_reveal_period)
+
+    # Process reveal
+    revealer.next_custody_reveal_period += 1
+
+    # Reward Block Preposer
+    proposer_index = get_beacon_proposer_index(state)
+    increase_balance(state, proposer_index, base_reward(state, index) // MINOR_REWARD_QUOTIENT)
+```
+
+##### Early derived secret reveals
+
+Verify that `len(block.body.early_derived_secret_reveals) <= MAX_EARLY_DERIVED_SECRET_REVEALS`.
+
+For each `reveal` in `block.body.early_derived_secret_reveals`, run the following function:
+
+```python
+def process_early_derived_secret_reveal(state: BeaconState,
+                              reveal: EarlyDerivedSecretReveal) -> None:
+    """
+    Process ``EarlyDerivedSecretReveal`` operation.
+    Note that this function mutates ``state``.
+    """
+
+    revealed_validator = state.validator_registry[reveal.revealed_index]
+    masker = state.validator_registry[reveal.masker_index]
+
+    assert reveal.epoch >= get_current_epoch(state) + RANDAO_PENALTY_EPOCHS
+    assert reveal.epoch < get_current_epoch(state) + EARLY_DERIVED_SECRET_PENALTY_MAX_FUTURE_EPOCHS
+    assert revealed_validator.slashed is False
+    assert reveal.revealed_index not in state.exposed_derived_secrets[reveal.epoch % EARLY_DERIVED_SECRET_PENALTY_MAX_FUTURE_EPOCHS]
+
+    # Verify signature correctness
+    masker = state.validator_registry[reveal.masker_index]
+    pubkeys = [revealed_validator.pubkey, masker.pubkey]
+    message_hashes = [
+        hash_tree_root(reveal.epoch),
+        reveal.mask,
+    ]
+
+    assert bls_verify_multiple(
+        pubkeys=pubkeys,
+        message_hashes=message_hashes,
+        signature=reveal.reveal,
+        domain=get_domain(
+            state=state,
+            domain_type=DOMAIN_RANDAO,
+            message_epoch=reveal.epoch,
+        ),
+    )
+
+    if reveal.epoch >= get_current_epoch(state) + CUSTODY_PERIOD_TO_RANDAO_PADDING:
+        # Full slashing when the secret was revealed so early it may be a valid custody
+        # round key
+        slash_validator(state, reveal.revealed_index, reveal.masker_index)
    else:
-        assert reveal.period > current_custody_period
-        assert revealer.slashed is False
-        slash_validator(state, reveal.revealer_index, reveal.masker_index)
+        # Only a small penalty proportional to proposer slot reward for RANDAO reveal 
+        # that does not interfere with the custody period
+        # The penalty is proportional to the max proposer reward 
+        
+        # Calculate penalty
+        max_proposer_slot_reward = (
+            get_base_reward(state, reveal.revealed_index) *
+            SLOTS_PER_EPOCH //
+            len(get_active_validator_indices(state, get_current_epoch(state))) //
+            PROPOSER_REWARD_QUOTIENT
+        )
+        penalty = max_proposer_slot_reward * EARLY_DERIVED_SECRET_REVEAL_SLOT_REWARD_MULTIPLE * (len(state.exposed_derived_secrets[reveal.epoch % EARLY_DERIVED_SECRET_PENALTY_MAX_FUTURE_EPOCHS]) + 1)
+
+        # Apply penalty
+        proposer_index = get_beacon_proposer_index(state)
+        whistleblower_index = reveal.masker_index
+        whistleblowing_reward = penalty // WHISTLEBLOWING_REWARD_QUOTIENT
+        proposer_reward = whistleblowing_reward // PROPOSER_REWARD_QUOTIENT
+        increase_balance(state, proposer_index, proposer_reward)
+        increase_balance(state, whistleblower_index, whistleblowing_reward - proposer_reward)
+        decrease_balance(state, reveal.revealed_index, penalty)
+
+        # Mark this derived secret as exposed so validator cannot be punished repeatedly 
+        state.exposed_derived_secrets[reveal.epoch % EARLY_DERIVED_SECRET_PENALTY_MAX_FUTURE_EPOCHS].append(reveal.revealed_index)
+
 ```

 #### Chunk challenges
@ -326,7 +463,7 @@ For each `challenge` in `block.body.custody_chunk_challenges`, run the following
 def process_chunk_challenge(state: BeaconState,
                            challenge: CustodyChunkChallenge) -> None:
    # Verify the attestation
-    assert verify_standalone_attestation(state, convert_to_standalone(state, challenge.attestation))
+    assert verify_indexed_attestation(state, convert_to_indexed(state, challenge.attestation))
    # Verify it is not too late to challenge
    assert slot_to_epoch(challenge.attestation.data.slot) >= get_current_epoch(state) - MAX_CHUNK_CHALLENGE_DELAY
    responder = state.validator_registry[challenge.responder_index]
@ -369,6 +506,7 @@ For each `challenge` in `block.body.custody_bit_challenges`, run the following f
 ```python
 def process_bit_challenge(state: BeaconState,
                          challenge: CustodyBitChallenge) -> None:
+
    # Verify challenge signature
    challenger = state.validator_registry[challenge.challenger_index]
    assert bls_verify(
@ -377,50 +515,63 @@ def process_bit_challenge(state: BeaconState,
        signature=challenge.signature,
        domain=get_domain(state, get_current_epoch(state), DOMAIN_CUSTODY_BIT_CHALLENGE),
    )
-    # Verify the challenger is not slashed
-    assert challenger.slashed is False
+    assert is_slashable_validator(challenger, get_current_epoch(state))
+
    # Verify the attestation
-    assert verify_standalone_attestation(state, convert_to_standalone(state, challenge.attestation))
+    assert verify_indexed_attestation(state, convert_to_indexed(state, challenge.attestation))
    # Verify the attestation is eligible for challenging
    responder = state.validator_registry[challenge.responder_index]
-    min_challengeable_epoch = responder.exit_epoch - EPOCHS_PER_CUSTODY_PERIOD * (1 + responder.max_reveal_lateness)
-    assert min_challengeable_epoch <= slot_to_epoch(challenge.attestation.data.slot)
+    assert (slot_to_epoch(challenge.attestation.data.slot) + responder.max_reveal_lateness <=
+            get_validators_custody_reveal_period(state, challenge.responder_index))
+
    # Verify the responder participated in the attestation
    attesters = get_attesting_indices(state, attestation.data, attestation.aggregation_bitfield)
    assert challenge.responder_index in attesters
+
    # A validator can be the challenger or responder for at most one challenge at a time
    for record in state.custody_bit_challenge_records:
        assert record.challenger_index != challenge.challenger_index
        assert record.responder_index != challenge.responder_index
-    # Verify the responder key
-    assert verify_custody_key(state, CustodyKeyReveal(
-        revealer_index=challenge.responder_index,
-        period=epoch_to_custody_period(slot_to_epoch(attestation.data.slot)),
-        key=challenge.responder_key,
-        masker_index=0,
-        mask=ZERO_HASH,
-    ))
+
+    # Verify the responder is a valid custody key
+    epoch_to_sign = get_randao_epoch_for_custody_period(
+        get_validators_custody_reveal_period(
+            state=state,
+            index=challenge.responder_index,
+            epoch=slot_to_epoch(attestation.data.slot),
+        challenge.responder_index
+    )
+    assert bls_verify(
+        pubkey=responder.pubkey,
+        message_hash=hash_tree_root(epoch_to_sign),
+        signature=challenge.responder_key,
+        domain=get_domain(
+            state=state,
+            domain_type=DOMAIN_RANDAO,
+            message_epoch=epoch_to_sign,
+        ),
+    )
+
    # Verify the chunk count
    chunk_count = get_custody_chunk_count(challenge.attestation)
    assert verify_bitfield(challenge.chunk_bits, chunk_count)
-    # Verify the xor of the chunk bits does not equal the custody bit
-    chunk_bits_xor = 0b0
-    for i in range(chunk_count):
-        chunk_bits_xor ^ get_bitfield_bit(challenge.chunk_bits, i)
+    # Verify the first bit of the hash of the chunk bits does not equal the custody bit
    custody_bit = get_bitfield_bit(attestation.custody_bitfield, attesters.index(responder_index))
-    assert custody_bit != chunk_bits_xor
+    assert custody_bit != get_bitfield_bit(get_chunk_bits_root(challenge.chunk_bits), 0)
    # Add new bit challenge record
    new_record = CustodyBitChallengeRecord(
        challenge_index=state.custody_challenge_index,
        challenger_index=challenge.challenger_index,
        responder_index=challenge.responder_index,
-        deadline=get_current_epoch(state) + CUSTODY_RESPONSE_DEADLINE
-        crosslink_data_root=challenge.attestation.crosslink_data_root,
-        chunk_bits=challenge.chunk_bits,
+        deadline=get_current_epoch(state) + CUSTODY_RESPONSE_DEADLINE,
+        crosslink_data_root=challenge.attestation.data.crosslink_data_root,
+        chunk_count=chunk_count,
+        chunk_bits_merkle_root=merkle_root(pad_to_power_of_2((challenge.chunk_bits))),
        responder_key=challenge.responder_key,
    )
    replace_empty_or_append(state.custody_bit_challenge_records, new_record)
    state.custody_challenge_index += 1
+
    # Postpone responder withdrawability
    responder.withdrawable_epoch = FAR_FUTURE_EPOCH
 ```
@ -451,10 +602,12 @@ def process_chunk_challenge_response(state: BeaconState,
                                     challenge: CustodyChunkChallengeRecord) -> None:
    # Verify chunk index
    assert response.chunk_index == challenge.chunk_index
+    # Verify bit challenge data is null
+    assert response.chunk_bits_branch == [] and response.chunk_bits_leaf == ZERO_HASH
    # Verify the chunk matches the crosslink data root
    assert verify_merkle_branch(
        leaf=hash_tree_root(response.chunk),
-        branch=response.branch,
+        branch=response.data_branch,
        depth=challenge.depth,
        index=response.chunk_index,
        root=challenge.crosslink_data_root,
@ -472,17 +625,25 @@ def process_bit_challenge_response(state: BeaconState,
                                   response: CustodyResponse,
                                   challenge: CustodyBitChallengeRecord) -> None:
    # Verify chunk index
-    assert response.chunk_index < len(challenge.chunk_bits)
+    assert response.chunk_index < challenge.chunk_count
    # Verify the chunk matches the crosslink data root
    assert verify_merkle_branch(
        leaf=hash_tree_root(response.chunk),
-        branch=response.branch,
-        depth=math.log2(next_power_of_two(len(challenge.chunk_bits))),
+        branch=response.data_branch,
+        depth=math.log2(next_power_of_two(challenge.chunk_count)),
        index=response.chunk_index,
        root=challenge.crosslink_data_root,
    )
+    # Verify the chunk bit leaf matches the challenge data
+    assert verify_merkle_branch(
+        leaf=response.chunk_bits_leaf,
+        branch=response.chunk_bits_branch,
+        depth=math.log2(next_power_of_two(challenge.chunk_count) // 256),
+        index=response.chunk_index // 256,
+        root=challenge.chunk_bits_merkle_root
+    )
    # Verify the chunk bit does not match the challenge chunk bit
-    assert get_custody_chunk_bit(challenge.responder_key, response.chunk) != get_bitfield_bit(challenge.chunk_bits, response.chunk_index)
+    assert get_custody_chunk_bit(challenge.responder_key, response.chunk) != get_bitfield_bit(challenge.chunk_bits_leaf, response.chunk_index % 256)
    # Clear the challenge
    records = state.custody_bit_challenge_records
    records[records.index(challenge)] = CustodyBitChallengeRecord()
@ -492,7 +653,20 @@ def process_bit_challenge_response(state: BeaconState,

 ## Per-epoch processing

-Run `process_challenge_deadlines(state)` immediately after `process_ejections(state)`:
+### Handling of custody-related deadlines
+
+ Run `process_reveal_deadlines(state)` immediately after `process_ejections(state)`:
+
+ ```python
+def process_reveal_deadlines(state: BeaconState) -> None:
+    for index, validator in enumerate(state.validator_registry):
+        if (validator.latest_custody_reveal_period +
+            (CUSTODY_RESPONSE_DEADLINE // EPOCHS_PER_CUSTODY_PERIOD) <
+            get_validators_custody_reveal_period(state, index)):
+                slash_validator(state, index)
+```
+
+Run `process_challenge_deadlines(state)` immediately after `process_reveal_deadlines(state)`:

 ```python
 def process_challenge_deadlines(state: BeaconState) -> None:
@ -509,16 +683,26 @@ def process_challenge_deadlines(state: BeaconState) -> None:
            records[records.index(challenge)] = CustodyBitChallengeRecord()
 ```

+Append this to `process_final_updates(state)`:
+
+```python
+    # Clean up exposed RANDAO key reveals
+    state.exposed_derived_secrets[current_epoch % EARLY_DERIVED_SECRET_PENALTY_MAX_FUTURE_EPOCHS] = []
+```
+
 In `process_penalties_and_exits`, change the definition of `eligible` to the following (note that it is not a pure function because `state` is declared in the surrounding scope):

 ```python
-def eligible(index):
+def eligible(state: BeaconState, index: ValidatorIndex) -> bool:
    validator = state.validator_registry[index]
    # Cannot exit if there are still open chunk challenges
    if len([record for record in state.custody_chunk_challenge_records if record.responder_index == index]) > 0:
        return False
+    # Cannot exit if there are still open bit challenges
+    if len([record for record in state.custody_bit_challenge_records if record.responder_index == index]) > 0:
+        return False
    # Cannot exit if you have not revealed all of your custody keys
-    elif epoch_to_custody_period(revealer.activation_epoch) + validator.custody_reveal_index <= epoch_to_custody_period(validator.exit_epoch):
+    elif validator.next_custody_reveal_period <= get_validators_custody_reveal_period(state, index, validator.exit_epoch):
        return False
    # Cannot exit if you already have
    elif validator.withdrawable_epoch < FAR_FUTURE_EPOCH:
--- a/specs/core/1_shard-data-chains.md
+++ b/specs/core/1_shard-data-chains.md
@ -1,13 +1,13 @@
 # Ethereum 2.0 Phase 1 -- Shard Data Chains

-**NOTICE**: This document is a work-in-progress for researchers and implementers.
+**Notice**: This document is a work-in-progress for researchers and implementers.

-## Table of Contents
+## Table of contents

 <!-- TOC -->

- [Ethereum 2.0 Phase 1 -- Shards Data Chains](#ethereum-20-phase-1----shard-data-chains)
-    - [Table of Contents](#table-of-contents)
+- [Ethereum 2.0 Phase 1 -- Shard Data Chains](#ethereum-20-phase-1----shard-data-chains)
+    - [Table of contents](#table-of-contents)
    - [Introduction](#introduction)
    - [Constants](#constants)
        - [Misc](#misc)
@ -53,8 +53,8 @@ This document describes the shard data layer and the shard fork choice rule in P

 | Name | Value | Unit | Duration |
 | - | - | :-: | :-: |
-| `CROSSLINK_LOOKBACK` | 2**0 (= 1) | epochs  | 6.2 minutes |
-| `PERSISTENT_COMMITTEE_PERIOD` | 2**11 (= 2,048) | epochs | ~9 days |
+| `CROSSLINK_LOOKBACK` | `2**0` (= 1) | epochs  | 6.2 minutes |
+| `PERSISTENT_COMMITTEE_PERIOD` | `2**11` (= 2,048) | epochs | ~9 days |

 ### Signature domains

@ -120,21 +120,15 @@ This document describes the shard data layer and the shard fork choice rule in P
 ### `get_period_committee`

 ```python
-def get_period_committee(state: BeaconState,
-                         shard: Shard,
-                         committee_start_epoch: Epoch,
-                         index: int,
-                         committee_count: int) -> List[ValidatorIndex]:
+def get_period_committee(state: BeaconState, epoch: Epoch, shard: Shard, index: int, count: int) -> List[ValidatorIndex]:
    """
    Return committee for a period. Used to construct persistent committees.
    """
-    active_validator_indices = get_active_validator_indices(state.validator_registry, committee_start_epoch)
-    seed = generate_seed(state, committee_start_epoch)
    return compute_committee(
-        validator_indices=active_validator_indices,
-        seed=seed,
-        index=shard * committee_count + index,
-        total_committees=SHARD_COUNT * committee_count,
+        indices=get_active_validator_indices(state, epoch),
+        seed=generate_seed(state, epoch),
+        index=shard * count + index,
+        count=SHARD_COUNT * count,
    )
 ```

@ -165,7 +159,7 @@ def get_persistent_committee(state: BeaconState,
        len(get_active_validator_indices(state.validator_registry, later_start_epoch)) //
        (SHARD_COUNT * TARGET_COMMITTEE_SIZE),
    ) + 1
-    
+
    index = slot % committee_count
    earlier_committee = get_period_committee(state, shard, earlier_start_epoch, index, committee_count)
    later_committee = get_period_committee(state, shard, later_start_epoch, index, committee_count)
@ -369,7 +363,7 @@ Let:
 * `shard_blocks` be the `ShardBlock` list such that `shard_blocks[slot]` is the canonical `ShardBlock` for shard `shard` at slot `slot`
 * `beacon_state` be the canonical `BeaconState`
 * `valid_attestations` be the list of valid `Attestation`, recursively defined
-* `candidate` be a candidate `Attestation` which is valid under phase 0 rules, and for which validity is to be determined under phase 1 rules by running `is_valid_beacon_attestation`
+* `candidate` be a candidate `Attestation` which is valid under Phase 0 rules, and for which validity is to be determined under Phase 1 rules by running `is_valid_beacon_attestation`

 ```python
 def is_valid_beacon_attestation(shard: Shard,
--- a/specs/light_client/merkle_proofs.md
+++ b/specs/light_client/merkle_proofs.md
@ -1,16 +1,19 @@
-**NOTICE**: This document is a work-in-progress for researchers and implementers.
+# Merkle proof formats

-## Table of Contents
+**Notice**: This document is a work-in-progress for researchers and implementers.
+
+## Table of contents
 <!-- TOC -->

- [Table of Contents](#table-of-contents)
- [Constants](#constants)
- [Generalized Merkle tree index](#generalized-merkle-tree-index)
- [SSZ object to index](#ssz-object-to-index)
- [Merkle multiproofs](#merkle-multiproofs)
- [MerklePartial](#merklepartial)
-    - [`SSZMerklePartial`](#sszmerklepartial)
-    - [Proofs for execution](#proofs-for-execution)
+- [Merkle proof formats](#merkle-proof-formats)
+   - [Table of contents](#table-of-contents)
+   - [Constants](#constants)
+   - [Generalized Merkle tree index](#generalized-merkle-tree-index)
+   - [SSZ object to index](#ssz-object-to-index)
+   - [Merkle multiproofs](#merkle-multiproofs)
+   - [MerklePartial](#merklepartial)
+       - [`SSZMerklePartial`](#sszmerklepartial)
+       - [Proofs for execution](#proofs-for-execution)

 <!-- /TOC -->

--- a/specs/light_client/sync_protocol.md
+++ b/specs/light_client/sync_protocol.md
@ -1,13 +1,13 @@
 # Beacon Chain Light Client Syncing

-__NOTICE__: This document is a work-in-progress for researchers and implementers. One of the design goals of the eth2 beacon chain is light-client friendliness, both to allow low-resource clients (mobile phones, IoT, etc) to maintain access to the blockchain in a reasonably safe way, but also to facilitate the development of "bridges" between the eth2 beacon chain and other chains.
+**Notice**: This document is a work-in-progress for researchers and implementers. One of the design goals of the Eth 2.0 beacon chain is light-client friendliness, not only to allow low-resource clients (mobile phones, IoT, etc.) to maintain access to the blockchain in a reasonably safe way, but also to facilitate the development of "bridges" between the Eth 2.0 beacon chain and other chains.

-## Table of Contents
+## Table of contents

 <!-- TOC -->

 - [Beacon Chain Light Client Syncing](#beacon-chain-light-client-syncing)
-    - [Table of Contents](#table-of-contents)
+    - [Table of contents](#table-of-contents)
    - [Preliminaries](#preliminaries)
        - [Expansions](#expansions)
        - [`get_active_validator_indices`](#get_active_validator_indices)
--- a/specs/networking/messaging.md
+++ b/specs/networking/messaging.md
@ -1,23 +1,22 @@
-ETH 2.0 Networking Spec - Messaging
-===
+# Eth 2.0 Networking Spec - Messaging

-# Abstract
+## Abstract

 This specification describes how individual Ethereum 2.0 messages are represented on the wire.

-The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL”, NOT", “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL” in this document are to be interpreted as described in RFC 2119.
+The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL”, NOT", “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL” in this document are to be interpreted as described in [RFC 2119](https://tools.ietf.org/html/rfc2119).

-# Motivation
+## Motivation

-This specification seeks to define a messaging protocol that is flexible enough to be changed easily as the ETH 2.0 specification evolves.
+This specification seeks to define a messaging protocol that is flexible enough to be changed easily as the Eth 2.0 specification evolves.

 Note that while `libp2p` is the chosen networking stack for Ethereum 2.0, as of this writing some clients do not have workable `libp2p` implementations. To allow those clients to communicate, we define a message envelope that includes the body's compression, encoding, and body length. Once `libp2p` is available across all implementations, this message envelope will be removed because `libp2p` will negotiate the values defined in the envelope upfront.

-# Specification
+## Specification

-## Message Structure
+### Message structure

-An ETH 2.0 message consists of an envelope that defines the message's compression, encoding, and length followed by the body itself.
+An Eth 2.0 message consists of an envelope that defines the message's compression, encoding, and length followed by the body itself.

 Visually, a message looks like this:

@ -35,12 +34,12 @@ Visually, a message looks like this:
 +--------------------------+
 ```

-Clients MUST ignore messages with mal-formed bodies. The compression/encoding nibbles MUST be one of the following values:
+Clients MUST ignore messages with malformed bodies. The compression/encoding nibbles MUST be one of the following values:

-## Compression Nibble Values
+### Compression nibble values

 - `0x0`: no compression

-## Encoding Nibble Values
+### Encoding nibble values

 - `0x1`: SSZ
--- a/specs/networking/node-identification.md
+++ b/specs/networking/node-identification.md
@ -1,13 +1,12 @@
-ETH 2.0 Networking Spec - Node Identification
-===
+# Eth 2.0 Networking Spec - Node Identification

-# Abstract
+## Abstract

 This specification describes how Ethereum 2.0 nodes identify and address each other on the network.

-The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL", NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119.
+The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL", NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC 2119](https://tools.ietf.org/html/rfc2119).

-# Specification
+## Specification

 Clients use Ethereum Node Records (as described in [EIP-778](http://eips.ethereum.org/EIPS/eip-778)) to discover one another. Each ENR includes, among other things, the following keys:

@ -21,11 +20,11 @@ The keys above are enough to construct a [multiaddr](https://github.com/multifor

 It is RECOMMENDED that clients set their TCP port to the default of `9000`.

-## Peer ID Generation
+### Peer ID generation

 The `libp2p` networking stack identifies peers via a "peer ID." Simply put, a node's Peer ID is the SHA2-256 `multihash` of the node's public key struct (serialized in protobuf, refer to the [Peer ID spec](https://github.com/libp2p/specs/pull/100)). `go-libp2p-crypto` contains the canonical implementation of how to hash `secp256k1` keys for use as a peer ID.

-# See Also
+## See also

 - [multiaddr](https://github.com/multiformats/multiaddr)
 - [multihash](https://multiformats.io/multihash/)
--- a/specs/networking/rpc-interface.md
+++ b/specs/networking/rpc-interface.md
@ -1,19 +1,18 @@
-ETH 2.0 Networking Spec - RPC Interface
-===
+# Eth 2.0 Networking Spec - RPC Interface

-# Abstract
+## Abstract

 The Ethereum 2.0 networking stack uses two modes of communication: a broadcast protocol that gossips information to interested parties via GossipSub, and an RPC protocol that retrieves information from specific clients. This specification defines the RPC protocol.

-The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL", NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119.
+The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL", NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC 2119](https://tools.ietf.org/html/rfc2119).

-# Dependencies
+## Dependencies

 This specification assumes familiarity with the [Messaging](./messaging.md), [Node Identification](./node-identification.md), and [Beacon Chain](../core/0_beacon-chain.md) specifications.

 # Specification

-## Message Schemas
+## Message schemas

 Message body schemas are notated like this:

@ -26,13 +25,13 @@ Message body schemas are notated like this:

 Embedded types are serialized as SSZ Containers unless otherwise noted.

-All referenced data structures can be found in the [0-beacon-chain](../core/0_beacon-chain.md#data-structures) specification.
+All referenced data structures can be found in the [Beacon Chain](../core/0_beacon-chain.md#data-structures) specification.

-## `libp2p` Protocol Names
+## `libp2p` protocol names

-A "Protocol ID" in `libp2p` parlance refers to a human-readable identifier `libp2p` uses in order to identify sub-protocols and stream messages of different types over the same connection. Peers exchange supported protocol IDs via the `Identify` protocol upon connection. When opening a new stream, peers pin a particular protocol ID to it, and the stream remains contextualised thereafter. Since messages are sent inside a stream, they do not need to bear the protocol ID.
+A "Protocol ID" in `libp2p` parlance refers to a human-readable identifier `libp2p` uses in order to identify sub-protocols and stream messages of different types over the same connection. Peers exchange supported protocol IDs via the `Identify` protocol upon connection. When opening a new stream, peers pin a particular protocol ID to it, and the stream remains contextualized thereafter. Since messages are sent inside a stream, they do not need to bear the protocol ID.

-## RPC-Over-`libp2p`
+## RPC-over-`libp2p`

 To facilitate RPC-over-`libp2p`, a single protocol name is used: `/eth/serenity/beacon/rpc/1`. The version number in the protocol name is neither backwards or forwards compatible, and will be incremented whenever changes to the below structures are required.

@ -88,7 +87,7 @@ The first 1,000 values in `response_code` are reserved for system use. The follo
 3. `30`: Method not found.
 4. `40`: Server error.

-### Alternative for Non-`libp2p` Clients
+### Alternative for non-`libp2p` clients

 Since some clients are waiting for `libp2p` implementations in their respective languages. As such, they MAY listen for raw TCP messages on port `9000`. To distinguish RPC messages from other messages on that port, a byte prefix of `ETH` (`0x455448`) MUST be prepended to all messages. This option will be removed once `libp2p` is ready in all supported languages.

@ -145,7 +144,7 @@ Root B          ^
       +---+
 ```

-Once the handshake completes, the client with the higher `latest_finalized_epoch` or `best_slot` (if the clients have equal `latest_finalized_epoch`s) SHOULD request beacon block roots from its counterparty via `beacon_block_roots` (i.e., RPC method `10`).
+Once the handshake completes, the client with the higher `latest_finalized_epoch` or `best_slot` (if the clients have equal `latest_finalized_epoch`s) SHOULD request beacon block roots from its counterparty via `beacon_block_roots` (i.e. RPC method `10`).

 ### Goodbye

@ -167,11 +166,11 @@ Client MAY send `goodbye` messages upon disconnection. The reason field MAY be o

 Clients MAY define custom goodbye reasons as long as the value is larger than `1000`.

-### Get Status
+### Get status

 **Method ID:** `2`

-**Request Body:**
+**Request body:**

 ```
 (
@ -181,7 +180,7 @@ Clients MAY define custom goodbye reasons as long as the value is larger than `1
 )
 ```

-**Response Body:**
+**Response body:**

 ```
 (
@ -193,11 +192,11 @@ Clients MAY define custom goodbye reasons as long as the value is larger than `1

 Returns metadata about the remote node.

-### Request Beacon Block Roots
+### Request beacon block roots

 **Method ID:** `10`

-**Request Body**
+**Request body**

 ```
 (
@ -206,7 +205,7 @@ Returns metadata about the remote node.
 )
 ```

-**Response Body:**
+**Response body:**

 ```
 # BlockRootSlot
@ -222,11 +221,11 @@ Returns metadata about the remote node.

 Requests a list of block roots and slots from the peer. The `count` parameter MUST be less than or equal to `32768`. The slots MUST be returned in ascending slot order.

-### Beacon Block Headers
+### Beacon block headers

 **Method ID:** `11`

-**Request Body**
+**Request body**

 ```
 (
@ -237,7 +236,7 @@ Requests a list of block roots and slots from the peer. The `count` parameter MU
 )
 ```

-**Response Body:**
+**Response body:**

 ```
 (
@ -245,15 +244,15 @@ Requests a list of block roots and slots from the peer. The `count` parameter MU
 )
 ```

-Requests beacon block headers from the peer starting from `(start_root, start_slot)`. The response MUST contain no more than `max_headers` headers. `skip_slots` defines the maximum number of slots to skip between blocks. For example, requesting blocks starting at slots `2` a `skip_slots` value of `1` would return the blocks at `[2, 4, 6, 8, 10]`. In cases where a slot is empty for a given slot number, the closest previous block MUST be returned. For example, if slot `4` were empty in the previous example, the returned array would contain `[2, 3, 6, 8, 10]`. If slot three were further empty, the array would contain `[2, 6, 8, 10]` - i.e., duplicate blocks MUST be collapsed. A `skip_slots` value of `0` returns all blocks.
+Requests beacon block headers from the peer starting from `(start_root, start_slot)`. The response MUST contain no more than `max_headers` headers. `skip_slots` defines the maximum number of slots to skip between blocks. For example, requesting blocks starting at slots `2` a `skip_slots` value of `1` would return the blocks at `[2, 4, 6, 8, 10]`. In cases where a slot is empty for a given slot number, the closest previous block MUST be returned. For example, if slot `4` were empty in the previous example, the returned array would contain `[2, 3, 6, 8, 10]`. If slot three were further empty, the array would contain `[2, 6, 8, 10]`—i.e. duplicate blocks MUST be collapsed. A `skip_slots` value of `0` returns all blocks.

 The function of the `skip_slots` parameter helps facilitate light client sync - for example, in [#459](https://github.com/ethereum/eth2.0-specs/issues/459) - and allows clients to balance the peers from whom they request headers. Clients could, for instance, request every 10th block from a set of peers where each peer has a different starting block in order to populate block data.

-### Beacon Block Bodies
+### Beacon block bodies

 **Method ID:** `12`

-**Request Body:**
+**Request body:**

 ```
 (
@ -261,7 +260,7 @@ The function of the `skip_slots` parameter helps facilitate light client sync -
 )
 ```

-**Response Body:**
+**Response body:**

 ```
 (
@ -269,15 +268,15 @@ The function of the `skip_slots` parameter helps facilitate light client sync -
 )
 ```

-Requests the `block_bodies` associated with the provided `block_roots` from the peer. Responses MUST return `block_roots` in the order provided in the request. If the receiver does not have a particular `block_root`, it must return a zero-value `block_body` (i.e., a `block_body` container with all zero fields).
+Requests the `block_bodies` associated with the provided `block_roots` from the peer. Responses MUST return `block_roots` in the order provided in the request. If the receiver does not have a particular `block_root`, it must return a zero-value `block_body` (i.e. a `block_body` container with all zero fields).

-### Beacon Chain State
+### Beacon chain state

-**Note:** This section is preliminary, pending the definition of the data structures to be transferred over the wire during fast sync operations.
+*Note*: This section is preliminary, pending the definition of the data structures to be transferred over the wire during fast sync operations.

 **Method ID:** `13`

-**Request Body:**
+**Request body:**

 ```
 (
@ -285,7 +284,7 @@ Requests the `block_bodies` associated with the provided `block_roots` from the
 )
 ```

-**Response Body:** TBD
+**Response body:** TBD

 Requests contain the hashes of Merkle tree nodes that when merkleized yield the block's `state_root`.

--- a/specs/simple-serialize.md
+++ b/specs/simple-serialize.md
@ -1,25 +1,28 @@
 # SimpleSerialize (SSZ)

-This is a **work in progress** describing typing, serialization and Merkleization of Ethereum 2.0 objects.
+**Notice**: This document is a work-in-progress describing typing, serialization, and Merkleization of Eth 2.0 objects.

 ## Table of contents
+<!-- TOC -->

- [Constants](#constants)
- [Typing](#typing)
-    - [Basic types](#basic-types)
-    - [Composite types](#composite-types)
-    - [Variable-size and fixed-size](#variable-size-and-fixed-size)
-    - [Aliases](#aliases)
-    - [Default values](#default-values)
-    - [Illegal types](#illegal-types)
- [Serialization](#serialization)
-    - [`"uintN"`](#uintn)
-    - [`"bool"`](#bool)
-    - [Vectors, containers, lists, unions](#vectors-containers-lists-unions)
- [Deserialization](#deserialization)
- [Merkleization](#merkleization)
- [Self-signed containers](#self-signed-containers)
- [Implementations](#implementations)
+- [SimpleSerialize (SSZ)](#simpleserialize-ssz)
+    - [Table of contents](#table-of-contents)
+    - [Constants](#constants)
+    - [Typing](#typing)
+        - [Basic types](#basic-types)
+        - [Composite types](#composite-types)
+        - [Aliases](#aliases)
+        - [Default values](#default-values)
+    - [Serialization](#serialization)
+        - [`"uintN"`](#uintn)
+        - [`"bool"`](#bool)
+        - [Vectors, containers, lists, unions](#vectors-containers-lists-unions)
+    - [Deserialization](#deserialization)
+    - [Merkleization](#merkleization)
+    - [Self-signed containers](#self-signed-containers)
+    - [Implementations](#implementations)
+
+<!-- /TOC -->

 ## Constants

@ -96,7 +99,7 @@ return b""
 ### Vectors, containers, lists, unions

 ```python
-# Reccursively serialize
+# Recursively serialize
 fixed_parts = [serialize(element) if not is_variable_size(element) else None for element in value]
 variable_parts = [serialize(element) if is_variable_size(element) else b"" for element in value]

@ -161,4 +164,4 @@ Let `value` be a self-signed container object. The convention is that the signat
 | Go | Prysm | Prysmatic Labs | [https://github.com/prysmaticlabs/prysm/tree/master/shared/ssz](https://github.com/prysmaticlabs/prysm/tree/master/shared/ssz) |
 | Swift | Yeeth | Dean Eigenmann | [https://github.com/yeeth/SimpleSerialize.swift](https://github.com/yeeth/SimpleSerialize.swift) |
 | C# | | Jordan Andrews | [https://github.com/codingupastorm/csharp-ssz](https://github.com/codingupastorm/csharp-ssz) |
-| C++ | | | [https://github.com/NAKsir-melody/cpp_ssz](https://github.com/NAKsir-melody/cpp_ssz) |
+| C++ | | Jiyun Kim | [https://github.com/NAKsir-melody/cpp_ssz](https://github.com/NAKsir-melody/cpp_ssz) |
--- a/specs/test_formats/README.md
+++ b/specs/test_formats/README.md
@ -1,17 +1,27 @@
 # General test format

-This document defines the YAML format and structure used for ETH 2.0 testing.
+This document defines the YAML format and structure used for Eth 2.0 testing.

-## ToC
+## Table of contents
+<!-- TOC -->

-* [About](#about)
-* [Glossary](#glossary)
-* [Test format philosophy](#test-format-philosophy)
-* [Test Suite](#test-suite)
-* [Config](#config)
-* [Fork-timeline](#fork-timeline)
-* [Config sourcing](#config-sourcing)
-* [Test structure](#test-structure)
+- [General test format](#general-test-format)
+    - [Table of contents](#table-of-contents)
+    - [About](#about)
+        - [Test-case formats](#test-case-formats)
+    - [Glossary](#glossary)
+    - [Test format philosophy](#test-format-philosophy)
+        - [Config design](#config-design)
+        - [Fork config design](#fork-config-design)
+        - [Test completeness](#test-completeness)
+    - [Test suite](#test-suite)
+    - [Config](#config)
+    - [Fork-timeline](#fork-timeline)
+    - [Config sourcing](#config-sourcing)
+    - [Test structure](#test-structure)
+    - [Note for implementers](#note-for-implementers)
+
+<!-- /TOC -->

 ## About

@ -52,28 +62,28 @@ Test formats:
 ### Config design

 After long discussion, the following types of configured constants were identified:
- Never changing: genesis data
+- Never changing: genesis data.
 - Changing, but reliant on old value: e.g. an epoch time may change, but if you want to do the conversion 
-  `(genesis data, timestamp) -> epoch number` you end up needing both constants.
+  `(genesis data, timestamp) -> epoch number`, you end up needing both constants.
 - Changing, but kept around during fork transition: finalization may take a while,
  e.g. an executable has to deal with new deposits and old deposits at the same time. Another example may be economic constants.
- Additional, back-wards compatible: new constants are introduced for later phases
+- Additional, backwards compatible: new constants are introduced for later phases.
 - Changing: there is a very small chance some constant may really be *replaced*. 
  In this off-chance, it is likely better to include it as an additional variable,
-  and some clients may simply stop supporting the old one, if they do not want to sync from genesis.
+  and some clients may simply stop supporting the old one if they do not want to sync from genesis.

 Based on these types of changes, we model the config as a list of key value pairs,
- that only grows with every fork (they may change in development versions of forks however, git manages this).
-With this approach, configurations are backwards compatible (older clients ignore unknown variables), and easy to maintain.
+ that only grows with every fork (they may change in development versions of forks, however; git manages this).
+With this approach, configurations are backwards compatible (older clients ignore unknown variables) and easy to maintain.

 ### Fork config design

 There are two types of fork-data:
-1) timeline: when does a fork take place?
-2) coverage: what forks are covered by a test?
+1) Timeline: When does a fork take place?
+2) Coverage: What forks are covered by a test?

 The first is neat to have as a separate form: we prevent duplication, and can run with different presets
- (e.g. fork timeline for a minimal local test, for a public testnet, or for mainnet)
+ (e.g. fork timeline for a minimal local test, for a public testnet, or for mainnet).

 The second does not affect the result of the tests, it just states what is covered by the tests,
 so that the right suites can be executed to see coverage for a certain fork.
@ -90,7 +100,7 @@ The aim is to provide clients with a well-defined scope of work to run a particu
 - Clients that are not complete in functionality can choose to ignore suites that use certain test-runners, or specific handlers of these test-runners.
 - Clients that are on older versions can test their work based on older releases of the generated tests, and catch up with newer releases when possible.

-## Test Suite
+## Test suite

 ```
 title: <string, short, one line> -- Display name for the test suite
@ -113,9 +123,9 @@ Separation of configuration and tests aims to:
 - Prevent duplication of configuration
 - Make all tests easy to upgrade (e.g. when a new config constant is introduced)
 - Clearly define which constants to use
- Shareable between clients, for cross-client short or long lived testnets
+- Shareable between clients, for cross-client short- or long-lived testnets
 - Minimize the amounts of different constants permutations to compile as a client.
-  Note: Some clients prefer compile-time constants and optimizations.
+  *Note*: Some clients prefer compile-time constants and optimizations.
  They should compile for each configuration once, and run the corresponding tests per build target.

 The format is described in [`configs/constant_presets`](../../configs/constant_presets/README.md#format).
@ -124,9 +134,9 @@ The format is described in [`configs/constant_presets`](../../configs/constant_p
 ## Fork-timeline

 A fork timeline is (preferably) loaded in as a configuration object into a client, as opposed to the constants configuration:
- - we do not allocate or optimize any code based on epoch numbers
- - when we transition from one fork to the other, it is preferred to stay online.
- - we may decide on an epoch number for a fork based on external events (e.g. Eth1 log event),
+ - We do not allocate or optimize any code based on epoch numbers.
+ - When we transition from one fork to the other, it is preferred to stay online.
+ - We may decide on an epoch number for a fork based on external events (e.g. Eth1 log event);
    a client should be able to activate a fork dynamically.

 The format is described in [`configs/fork_timelines`](../../configs/fork_timelines/README.md#format).
--- a/specs/test_formats/bls/README.md
+++ b/specs/test_formats/bls/README.md
@ -1,7 +1,7 @@
 # BLS tests

 A test type for BLS. Primarily geared towards verifying the *integration* of any BLS library.
-We do not recommend to roll your own crypto, or use an untested BLS library.
+We do not recommend rolling your own crypto or using an untested BLS library.

 The BLS test suite runner has the following handlers:

@ -12,4 +12,4 @@ The BLS test suite runner has the following handlers:
 - [`priv_to_pub`](./priv_to_pub.md)
 - [`sign_msg`](./sign_msg.md)

-Note: signature-verification and aggregate-verify test cases are not yet supported.
+*Note*: Signature-verification and aggregate-verify test cases are not yet supported.
--- a/specs/test_formats/shuffling/README.md
+++ b/specs/test_formats/shuffling/README.md
@ -1,16 +1,16 @@
 # Test format: shuffling

-The runner of the Shuffling test type has only one handler: `core`
+The runner of the Shuffling test type has only one handler: `core`.

-This does not mean however that testing is limited.
+However, this does not mean that testing is limited.
 Clients may take different approaches to shuffling, for optimizing,
 and supporting advanced lookup behavior back in older history.

 For implementers, possible test runners implementing testing can include:
-1) just test permute-index, run it for each index `i` in `range(count)`, and check against expected `output[i]` (default spec implementation)
-2) test un-permute-index (the reverse lookup. Implemented by running the shuffling rounds in reverse: from `round_count-1` to `0`)
-3) test the optimized complete shuffle, where all indices are shuffled at once, test output in one go.
-4) test complete shuffle in reverse (reverse rounds, same as 2)
+1) Just test permute-index, run it for each index `i` in `range(count)`, and check against expected `output[i]` (default spec implementation).
+2) Test un-permute-index (the reverse lookup; implemented by running the shuffling rounds in reverse, from `round_count-1` to `0`).
+3) Test the optimized complete shuffle, where all indices are shuffled at once; test output in one go.
+4) Test complete shuffle in reverse (reverse rounds, same as #2).

 ## Test case format

--- a/specs/test_formats/ssz_generic/README.md
+++ b/specs/test_formats/ssz_generic/README.md
@ -3,7 +3,7 @@
 This set of test-suites provides general testing for SSZ:
 to instantiate any container/list/vector/other type from binary data.

-Since SSZ is in a development-phase, not the full suite of features is covered yet.
+Since SSZ is in a development-phase, the full suite of features is not covered yet.
 Note that these tests are based on the older SSZ package.
 The tests are still relevant, but limited in scope:
 more complex object encodings have changed since the original SSZ testing.
@ -11,10 +11,10 @@ The tests are still relevant, but limited in scope:
 A minimal but useful series of tests covering `uint` encoding and decoding is provided.
 This is a direct port of the older SSZ `uint` tests (minus outdated test cases).

-[uint test format](./uint.md).
+Test format documentation can be found here: [uint test format](./uint.md).

-Note: the current phase-0 spec does not use larger uints, and uses byte vectors (fixed length) instead to represent roots etc.
+*Note*: The current Phase 0 spec does not use larger uints, and uses byte vectors (fixed length) instead to represent roots etc.
 The exact uint lengths to support may be redefined in the future.

-Extension of the SSZ tests collection is planned, with an update to the new spec-maintained `minimal_ssz.py`,
+Extension of the SSZ tests collection is planned, with an update to the new spec-maintained `minimal_ssz.py`;
 see CI/testing issues for progress tracking.
--- a/specs/test_formats/ssz_static/README.md
+++ b/specs/test_formats/ssz_static/README.md
@ -1,7 +1,7 @@
 # SSZ, static tests

 This set of test-suites provides static testing for SSZ:
- to instantiate just the known ETH-2.0 SSZ types from binary data.
+ to instantiate just the known Eth 2.0 SSZ types from binary data.

 This series of tests is based on the spec-maintained `minimal_ssz.py`, i.e. fully consistent with the SSZ spec. 

--- a/specs/test_formats/ssz_static/core.md
+++ b/specs/test_formats/ssz_static/core.md
@ -1,7 +1,7 @@
 # Test format: SSZ static types

 The goal of this type is to provide clients with a solid reference for how the known SSZ objects should be encoded.
-Each object described in the Phase-0 spec is covered.
+Each object described in the Phase 0 spec is covered.
 This is important, as many of the clients aiming to serialize/deserialize objects directly into structs/classes
 do not support (or have alternatives for) generic SSZ encoding/decoding.
 This test-format ensures these direct serializations are covered.
@ -27,6 +27,6 @@ A test-runner can implement the following assertions:
 ## References


-**`serialized`**: [SSZ serialization](../../simple-serialize.md#serialization)   
-**`root`** - [hash_tree_root](../../simple-serialize.md#merkleization) function  
-**`signing_root`** - [signing_root](../../simple-serialize.md#self-signed-containers) function
+**`serialized`**—[SSZ serialization](../../simple-serialize.md#serialization)   
+**`root`**—[hash_tree_root](../../simple-serialize.md#merkleization) function  
+**`signing_root`**—[signing_root](../../simple-serialize.md#self-signed-containers) function
--- a/specs/validator/0_beacon-chain-validator.md
+++ b/specs/validator/0_beacon-chain-validator.md
@ -1,13 +1,13 @@
 # Ethereum 2.0 Phase 0 -- Honest Validator

-__NOTICE__: This document is a work-in-progress for researchers and implementers. This is an accompanying document to [Ethereum 2.0 Phase 0 -- The Beacon Chain](../core/0_beacon-chain.md) that describes the expected actions of a "validator" participating in the Ethereum 2.0 protocol.
+**Notice**: This document is a work-in-progress for researchers and implementers. This is an accompanying document to [Ethereum 2.0 Phase 0 -- The Beacon Chain](../core/0_beacon-chain.md), which describes the expected actions of a "validator" participating in the Ethereum 2.0 protocol.

-## Table of Contents
+## Table of contents

 <!-- TOC -->

 - [Ethereum 2.0 Phase 0 -- Honest Validator](#ethereum-20-phase-0----honest-validator)
-    - [Table of Contents](#table-of-contents)
+    - [Table of contents](#table-of-contents)
    - [Introduction](#introduction)
    - [Prerequisites](#prerequisites)
    - [Constants](#constants)
@ -96,21 +96,21 @@ The validator constructs their `withdrawal_credentials` via the following:

 ### Submit deposit

-In phase 0, all incoming validator deposits originate from the Ethereum 1.0 PoW chain. Deposits are made to the [deposit contract](../core/0_deposit-contract.md) located at `DEPOSIT_CONTRACT_ADDRESS`.
+In Phase 0, all incoming validator deposits originate from the Ethereum 1.0 PoW chain. Deposits are made to the [deposit contract](../core/0_deposit-contract.md) located at `DEPOSIT_CONTRACT_ADDRESS`.

 To submit a deposit:

 * Pack the validator's [initialization parameters](#initialization) into `deposit_data`, a [`DepositData`](../core/0_beacon-chain.md#depositdata) SSZ object.
-* Let `amount` be the amount in Gwei to be deposited by the validator where `MIN_DEPOSIT_AMOUNT <= amount <= MAX_DEPOSIT_AMOUNT`.
+* Let `amount` be the amount in Gwei to be deposited by the validator where `MIN_DEPOSIT_AMOUNT <= amount <= MAX_EFFECTIVE_BALANCE`.
 * Set `deposit_data.amount = amount`.
 * Let `signature` be the result of `bls_sign` of the `signing_root(deposit_data)` with `domain=DOMAIN_DEPOSIT`.
 * Send a transaction on the Ethereum 1.0 chain to `DEPOSIT_CONTRACT_ADDRESS` executing `def deposit(pubkey: bytes[48], withdrawal_credentials: bytes[32], signature: bytes[96])` along with a deposit of `amount` Gwei.

-_Note_: Deposits made for the same `pubkey` are treated as for the same validator. A singular `Validator` will be added to `state.validator_registry` with each additional deposit amount added to the validator's balance. A validator can only be activated when total deposits for the validator pubkey meet or exceed `MAX_DEPOSIT_AMOUNT`.
+*Note*: Deposits made for the same `pubkey` are treated as for the same validator. A singular `Validator` will be added to `state.validator_registry` with each additional deposit amount added to the validator's balance. A validator can only be activated when total deposits for the validator pubkey meet or exceed `MAX_EFFECTIVE_BALANCE`.

 ### Process deposit

-Deposits cannot be processed into the beacon chain until the eth1.0 block in which they were deposited or any of its descendants is added to the beacon chain `state.eth1_data`. This takes _a minimum_ of `ETH1_FOLLOW_DISTANCE` eth1.0 blocks (~4 hours) plus `ETH1_DATA_VOTING_PERIOD` epochs (~1.7 hours). Once the requisite eth1.0 data is added, the deposit will normally be added to a beacon chain block and processed into the `state.validator_registry` within an epoch or two. The validator is then in a queue to be activated.
+Deposits cannot be processed into the beacon chain until the Eth 1.0 block in which they were deposited or any of its descendants is added to the beacon chain `state.eth1_data`. This takes _a minimum_ of `ETH1_FOLLOW_DISTANCE` Eth 1.0 blocks (~4 hours) plus `ETH1_DATA_VOTING_PERIOD` epochs (~1.7 hours). Once the requisite Eth 1.0 data is added, the deposit will normally be added to a beacon chain block and processed into the `state.validator_registry` within an epoch or two. The validator is then in a queue to be activated.

 ### Validator index

@ -130,11 +130,11 @@ is_active = is_active_validator(validator, shuffling_epoch)

 Once a validator is activated, the validator is assigned [responsibilities](#beacon-chain-responsibilities) until exited.

-_Note_: There is a maximum validator churn per finalized epoch so the delay until activation is variable depending upon finality, total active validator balance, and the number of validators in the queue to be activated.
+*Note*: There is a maximum validator churn per finalized epoch so the delay until activation is variable depending upon finality, total active validator balance, and the number of validators in the queue to be activated.

 ## Beacon chain responsibilities

-A validator has two primary responsibilities to the beacon chain -- [proposing blocks](block-proposal) and [creating attestations](attestations-1). Proposals happen infrequently, whereas attestations should be created once per epoch.
+A validator has two primary responsibilities to the beacon chain: [proposing blocks](#block-proposal) and [creating attestations](#attestations-1). Proposals happen infrequently, whereas attestations should be created once per epoch.

 ### Block proposal

@ -148,7 +148,7 @@ There is one proposer per slot, so if there are N active validators any individu

 Set `block.slot = slot` where `slot` is the current slot at which the validator has been selected to propose. The `parent` selected must satisfy that `parent.slot < block.slot`.

-_Note:_ there might be "skipped" slots between the `parent` and `block`. These skipped slots are processed in the state transition function without per-block processing.
+*Note*: There might be "skipped" slots between the `parent` and `block`. These skipped slots are processed in the state transition function without per-block processing.

 ##### Parent root

@ -158,7 +158,7 @@ Set `block.previous_block_root = signing_root(parent)`.

 Set `block.state_root = hash_tree_root(state)` of the resulting `state` of the `parent -> block` state transition.

-_Note_: To calculate `state_root`, the validator should first run the state transition function on an unsigned `block` containing a stub for the `state_root`. It is useful to be able to run a state transition function that does _not_ validate signatures or state root for this purpose.
+*Note*: To calculate `state_root`, the validator should first run the state transition function on an unsigned `block` containing a stub for the `state_root`. It is useful to be able to run a state transition function that does _not_ validate signatures or state root for this purpose.

 ##### Randao reveal

@ -181,12 +181,12 @@ epoch_signature = bls_sign(
 `block.eth1_data` is a mechanism used by block proposers vote on a recent Ethereum 1.0 block hash and an associated deposit root found in the Ethereum 1.0 deposit contract. When consensus is formed, `state.latest_eth1_data` is updated, and validator deposits up to this root can be processed. The deposit root can be calculated by calling the `get_deposit_root()` function of the deposit contract using the post-state of the block hash.

 * Let `D` be the set of `Eth1DataVote` objects `vote` in `state.eth1_data_votes` where:
-    * `vote.eth1_data.block_hash` is the hash of an eth1.0 block that is (i) part of the canonical chain, (ii) >= `ETH1_FOLLOW_DISTANCE` blocks behind the head, and (iii) newer than `state.latest_eth1_data.block_data`.
-    * `vote.eth1_data.deposit_count` is the deposit count of the eth1.0 deposit contract at the block defined by `vote.eth1_data.block_hash`.
-    * `vote.eth1_data.deposit_root` is the deposit root of the eth1.0 deposit contract at the block defined by `vote.eth1_data.block_hash`.
+    * `vote.eth1_data.block_hash` is the hash of an Eth 1.0 block that is (i) part of the canonical chain, (ii) >= `ETH1_FOLLOW_DISTANCE` blocks behind the head, and (iii) newer than `state.latest_eth1_data.block_hash`.
+    * `vote.eth1_data.deposit_count` is the deposit count of the Eth 1.0 deposit contract at the block defined by `vote.eth1_data.block_hash`.
+    * `vote.eth1_data.deposit_root` is the deposit root of the Eth 1.0 deposit contract at the block defined by `vote.eth1_data.block_hash`.
 * If `D` is empty:
-    * Let `block_hash` be the block hash of the `ETH1_FOLLOW_DISTANCE`'th ancestor of the head of the canonical eth1.0 chain.
-    * Let `deposit_root` and `deposit_count` be the deposit root and deposit count of the eth1.0 deposit contract in the post-state of the block referenced by `block_hash`
+    * Let `block_hash` be the block hash of the `ETH1_FOLLOW_DISTANCE`'th ancestor of the head of the canonical Eth 1.0 chain.
+    * Let `deposit_root` and `deposit_count` be the deposit root and deposit count of the Eth 1.0 deposit contract in the post-state of the block referenced by `block_hash`
    * Let `best_vote_data = Eth1Data(block_hash=block_hash, deposit_root=deposit_root, deposit_count=deposit_count)`.
 * If `D` is nonempty:
    * Let `best_vote_data` be the `eth1_data` of the member of `D` that has the highest `vote.vote_count`, breaking ties by favoring block hashes with higher associated block height.
@ -224,7 +224,7 @@ Up to `MAX_ATTESTATIONS` aggregate attestations can be included in the `block`.

 ##### Deposits

-If there are any unprocessed deposits for the existing `state.latest_eth1_data` (i.e. `state.latest_eth1_data.deposit_count > state.deposit_index`), then pending deposits _must_ be added to the block. The expected number of deposits is exactly `min(MAX_DEPOSITS, latest_eth1_data.deposit_count - state.deposit_index)`.  These [`deposits`](../core/0_beacon-chain.md#deposit) are constructed from the `Deposit` logs from the [Eth1.0 deposit contract](../core/0_deposit-contract.md) and must be processed in sequential order. The deposits included in the `block` must satisfy the verification conditions found in [deposits processing](../core/0_beacon-chain.md#deposits).
+If there are any unprocessed deposits for the existing `state.latest_eth1_data` (i.e. `state.latest_eth1_data.deposit_count > state.deposit_index`), then pending deposits _must_ be added to the block. The expected number of deposits is exactly `min(MAX_DEPOSITS, latest_eth1_data.deposit_count - state.deposit_index)`.  These [`deposits`](../core/0_beacon-chain.md#deposit) are constructed from the `Deposit` logs from the [Eth 1.0 deposit contract](../core/0_deposit-contract) and must be processed in sequential order. The deposits included in the `block` must satisfy the verification conditions found in [deposits processing](../core/0_beacon-chain.md#deposits).

 The `proof` for each deposit must be constructed against the deposit root contained in `state.latest_eth1_data` rather than the deposit root at the time the deposit was initially logged from the 1.0 chain. This entails storing a full deposit merkle tree locally and computing updated proofs against the `latest_eth1_data.deposit_root` as needed. See [`minimal_merkle.py`](https://github.com/ethereum/research/blob/master/spec_pythonizer/utils/merkle_minimal.py) for a sample implementation.

@ -236,7 +236,7 @@ Up to `MAX_VOLUNTARY_EXITS` [`VoluntaryExit`](../core/0_beacon-chain.md#voluntar

 A validator is expected to create, sign, and broadcast an attestation during each epoch. The slot during which the validator performs this role is any slot at which `get_crosslink_committees_at_slot(state, slot)` contains a committee that contains `validator_index`.

-A validator should create and broadcast the attestation halfway through the `slot` during which the validator is assigned -- that is `SECONDS_PER_SLOT * 0.5` seconds after the start of `slot`.
+A validator should create and broadcast the attestation halfway through the `slot` during which the validator is assigned ― that is, `SECONDS_PER_SLOT * 0.5` seconds after the start of `slot`.

 #### Attestation data

@ -265,7 +265,7 @@ Set `attestation_data.source_root = head_state.current_justified_root`.

 Set `attestation_data.target_root = signing_root(epoch_boundary)` where `epoch_boundary` is the block at the most recent epoch boundary.

-_Note:_ This can be looked up in the state using:
+*Note*: This can be looked up in the state using:
 * Let `epoch_start_slot = get_epoch_start_slot(get_current_epoch(head_state))`.
 * Set `epoch_boundary = head if epoch_start_slot == head_state.slot else get_block_root(state, epoch_start_slot)`.

@ -281,7 +281,7 @@ Set `attestation_data.previous_crosslink_root = hash_tree_root(head_state.curren

 Set `attestation_data.crosslink_data_root = ZERO_HASH`.

-_Note:_ This is a stub for phase 0.
+*Note*: This is a stub for Phase 0.

 #### Construct attestation

@ -298,14 +298,14 @@ Set `attestation.data = attestation_data` where `attestation_data` is the `Attes
 * Set `aggregation_bitfield[index_into_committee // 8] |= 2 ** (index_into_committee % 8)`.
 * Set `attestation.aggregation_bitfield = aggregation_bitfield`.

-_Note_: Calling `get_attesting_indices(state, attestation.data, attestation.aggregation_bitfield)` should return a list of length equal to 1, containing `validator_index`.
+*Note*: Calling `get_attesting_indices(state, attestation.data, attestation.aggregation_bitfield)` should return a list of length equal to 1, containing `validator_index`.

 ##### Custody bitfield

 * Let `custody_bitfield` be a byte array filled with zeros of length `(len(committee) + 7) // 8`.
 * Set `attestation.custody_bitfield = custody_bitfield`.

-_Note:_ This is a stub for phase 0.
+*Note*: This is a stub for Phase 0.

 ##### Aggregate signature

@ -379,14 +379,14 @@ def is_proposer_at_slot(state: BeaconState,
    return get_beacon_proposer_index(state) == validator_index
 ```

-_Note_: To see if a validator is assigned to proposer during the slot, the validator must run an empty slot transition from the previous state to the current slot.
+*Note*: To see if a validator is assigned to proposer during the slot, the validator must run an empty slot transition from the previous state to the current slot.


 ### Lookahead

-The beacon chain shufflings are designed to provide a minimum of 1 epoch lookahead on the validator's upcoming committee assignments for attesting dictated by the shuffling and slot. Note that this lookahead does not apply to proposing which must checked during the slot in question.
+The beacon chain shufflings are designed to provide a minimum of 1 epoch lookahead on the validator's upcoming committee assignments for attesting dictated by the shuffling and slot. Note that this lookahead does not apply to proposing, which must checked during the slot in question.

-`get_committee_assignment` should be called at the start of each epoch to get the assignment for the next epoch (`current_epoch + 1`). A validator should plan for future assignments which involves noting at which future slot one will have to attest and also which shard one should begin syncing (in phase 1+).
+`get_committee_assignment` should be called at the start of each epoch to get the assignment for the next epoch (`current_epoch + 1`). A validator should plan for future assignments which involves noting at which future slot one will have to attest and also which shard one should begin syncing (in Phase 1+).

 Specifically, a validator should call `get_committee_assignment(state, next_epoch, validator_index)` when checking for next epoch assignments.

@ -394,26 +394,26 @@ Specifically, a validator should call `get_committee_assignment(state, next_epoc

 "Slashing" is the burning of some amount of validator funds and immediate ejection from the active validator set. In Phase 0, there are two ways in which funds can be slashed -- [proposer slashing](#proposer-slashing) and [attester slashing](#attester-slashing). Although being slashed has serious repercussions, it is simple enough to avoid being slashed all together by remaining _consistent_ with respect to the messages a validator has previously signed.

-_Note_: Signed data must be within a sequential `Fork` context to conflict. Messages cannot be slashed across diverging forks. If the previous fork version is 1 and the chain splits into fork 2 and 102, messages from 1 can slashable against messages in forks 1, 2, and 102. Messages in 2 cannot be slashable against messages in 102 and vice versa.
+*Note*: Signed data must be within a sequential `Fork` context to conflict. Messages cannot be slashed across diverging forks. If the previous fork version is 1 and the chain splits into fork 2 and 102, messages from 1 can slashable against messages in forks 1, 2, and 102. Messages in 2 cannot be slashable against messages in 102 and vice versa.

 ### Proposer slashing

 To avoid "proposer slashings", a validator must not sign two conflicting [`BeaconBlock`](../core/0_beacon-chain.md#beaconblock) where conflicting is defined as two distinct blocks within the same epoch.

-_In phase 0, as long as the validator does not sign two different beacon blocks for the same epoch, the validator is safe against proposer slashings._
+*In Phase 0, as long as the validator does not sign two different beacon blocks for the same epoch, the validator is safe against proposer slashings.*

-Specifically, when signing an `BeaconBlock`, a validator should perform the following steps in the following order:
-1. Save a record to hard disk that an beacon block has been signed for the `epoch=slot_to_epoch(block.slot)`.
+Specifically, when signing a `BeaconBlock`, a validator should perform the following steps in the following order:
+1. Save a record to hard disk that a beacon block has been signed for the `epoch=slot_to_epoch(block.slot)`.
 2. Generate and broadcast the block.

-If the software crashes at some point within this routine, then when the validator comes back online the hard disk has the record of the _potentially_ signed/broadcast block and can effectively avoid slashing.
+If the software crashes at some point within this routine, then when the validator comes back online the hard disk has the record of the *potentially* signed/broadcast block and can effectively avoid slashing.

 ### Attester slashing

-To avoid "attester slashings", a validator must not sign two conflicting [`AttestationData`](../core/0_beacon-chain.md#attestationdata) objects where conflicting is defined as a set of two attestations that satisfy either [`is_double_vote`](../core/0_beacon-chain.md#is_double_vote) or [`is_surround_vote`](../core/0_beacon-chain.md#is_surround_vote).
+To avoid "attester slashings", a validator must not sign two conflicting [`AttestationData`](../core/0_beacon-chain.md#attestationdata) objects, i.e. two attestations that satisfy [`is_slashable_attestation_data`](../core/0_beacon-chain.md#is_slashable_attestation_data).

 Specifically, when signing an `Attestation`, a validator should perform the following steps in the following order:
 1. Save a record to hard disk that an attestation has been signed for source -- `attestation_data.source_epoch` -- and target -- `slot_to_epoch(attestation_data.slot)`.
 2. Generate and broadcast attestation.

-If the software crashes at some point within this routine, then when the validator comes back online the hard disk has the record of the _potentially_ signed/broadcast attestation and can effectively avoid slashing.
+If the software crashes at some point within this routine, then when the validator comes back online the hard disk has the record of the *potentially* signed/broadcast attestation and can effectively avoid slashing.
--- a/test_generators/README.md
+++ b/test_generators/README.md
@ -1,23 +1,22 @@
-# Eth2.0 Test Generators
+# Eth 2.0 Test Generators

 This directory contains all the generators for YAML tests, consumed by Eth 2.0 client implementations.

-Any issues with the generators and/or generated tests should be filed
- in the repository that hosts the generator outputs, here: [ethereum/eth2.0-tests](https://github.com/ethereum/eth2.0-tests/).
+Any issues with the generators and/or generated tests should be filed in the repository that hosts the generator outputs, here: [ethereum/eth2.0-spec-tests](https://github.com/ethereum/eth2.0-spec-tests).

-Whenever a release is made, the new tests are automatically built and
+Whenever a release is made, the new tests are automatically built, and
 [eth2TestGenBot](https://github.com/eth2TestGenBot) commits the changes to the test repository.

 ## How to run generators

-pre-requisites:
+Prerequisites:
 - Python 3 installed
 - PIP 3
- GNU make
+- GNU Make

 ### Cleaning

-This removes the existing virtual environments (`/test_generators/<generator>/venv`), and generated tests (`/yaml_tests/`).
+This removes the existing virtual environments (`/test_generators/<generator>/venv`) and generated tests (`/yaml_tests/`).

 ```bash
 make clean 
@ -25,7 +24,7 @@ make clean

 ### Running all test generators

-This runs all the generators.
+This runs all of the generators.

 ```bash
 make -j 4 gen_yaml_tests
@ -36,8 +35,7 @@ The `-j N` flag makes the generators run in parallel, with `N` being the amount

 ### Running a single generator

-The make file auto-detects generators in the `test_generators/` directory,
- and provides a tests-gen target for each generator, see example.
+The makefile auto-detects generators in the `test_generators` directory and provides a tests-gen target for each generator. See example:

 ```bash
 make ./yaml_tests/shuffling/
@ -45,7 +43,7 @@ make ./yaml_tests/shuffling/

 ## Developing a generator

-Simply open up the generator (not all at once) of choice in your favorite IDE/editor, and run:
+Simply open up the generator (not all at once) of choice in your favorite IDE/editor and run:

 ```bash
 # From the root of the generator directory:
@ -65,19 +63,19 @@ eth-utils==1.4.1
 ../../test_libs/config_helpers
 ../../test_libs/pyspec
 ```
-The config helper and pyspec is optional, but preferred. We encourage generators to derive tests from the spec itself, to prevent code duplication and outdated tests.
-Applying configurations to the spec is simple, and enables you to create test suites with different contexts.
+The config helper and pyspec is optional, but preferred. We encourage generators to derive tests from the spec itself in order to prevent code duplication and outdated tests.
+Applying configurations to the spec is simple and enables you to create test suites with different contexts.

-Note: make sure to run `make pyspec` from the root of the specs repository, to build the pyspec requirement.
+*Note*: Make sure to run `make pyspec` from the root of the specs repository in order to build the pyspec requirement.

 Install all the necessary requirements (re-run when you add more):
 ```bash
-pip3 install -e .[pyspec]
+pip3 install -r requirements.txt
 ```

 And write your initial test generator, extending the base generator:

-Write a `main.py` file, here's an example:
+Write a `main.py` file. See example:

 ```python
 from gen_base import gen_runner, gen_suite, gen_typing
@ -134,33 +132,33 @@ if __name__ == "__main__":
 ```

 Recommendations:
- you can have more than just 1 suite creator, e.g. ` gen_runner.run_generator("foo", [bar_test_suite, abc_test_suite, example_test_suite])`
- you can concatenate lists of test cases, if you don't want to split it up in suites, however make sure they could be run with one handler.
- you can split your suite creators into different python files/packages, good for code organization.
- use config "minimal" for performance. But also implement a suite with the default config where necessary. 
- you may be able to write your test suite creator in a way where it does not make assumptions on constants.
+- You can have more than just one suite creator, e.g. ` gen_runner.run_generator("foo", [bar_test_suite, abc_test_suite, example_test_suite])`.
+- You can concatenate lists of test cases if you don't want to split it up in suites, however, make sure they can be run with one handler.
+- You can split your suite creators into different Python files/packages; this is good for code organization.
+- Use config "minimal" for performance, but also implement a suite with the default config where necessary. 
+- You may be able to write your test suite creator in a way where it does not make assumptions on constants.
  If so, you can generate test suites with different configurations for the same scenario (see example). 
- the test-generator accepts `--output` and `--force` (overwrite output)
+- The test-generator accepts `--output` and `--force` (overwrite output).

 ## How to add a new test generator

-In order to add a new test generator that builds `New Tests`:
+To add a new test generator that builds `New Tests`:

-1. Create a new directory `new_tests`, within the `test_generators` directory.
+1. Create a new directory `new_tests` within the `test_generators` directory.
 Note that `new_tests` is also the name of the directory in which the tests will appear in the tests repository later.
 2. Your generator is assumed to have a `requirements.txt` file,
 with any dependencies it may need. Leave it empty if your generator has none.
 3. Your generator is assumed to have a `main.py` file in its root.
 By adding the base generator to your requirements, you can make a generator really easily. See docs below.
 4. Your generator is called with `-o some/file/path/for_testing/can/be_anything -c some/other/path/to_configs/`.
- The base generator helps you handle this; you only have to define suite headers,
+ The base generator helps you handle this; you only have to define suite headers
 and a list of tests for each suite you generate.
 5. Finally, add any linting or testing commands to the
 [circleci config file](https://github.com/ethereum/eth2.0-test-generators/blob/master/.circleci/config.yml)
 if desired to increase code quality.

-Note: you do not have to change the makefile.
-However, if necessary (e.g. not using python, or mixing in other languages), submit an issue, and it can be a special case.
+*Note*: You do not have to change the makefile.
+However, if necessary (e.g. not using Python, or mixing in other languages), submit an issue, and it can be a special case.
 Do note that generators should be easy to maintain, lean, and based on the spec.


@ -168,6 +166,6 @@ Do note that generators should be easy to maintain, lean, and based on the spec.

 If a test generator is not needed anymore, undo the steps described above and make a new release:

-1. remove the generator directory
-2. remove the generated tests in the `eth2.0-tests` repository by opening a PR there.
-3. make a new release
+1. Remove the generator directory.
+2. Remove the generated tests in the [`eth2.0-spec-tests`](https://github.com/ethereum/eth2.0-spec-tests) repository by opening a pull request there.
+3. Make a new release.
--- a/test_generators/operations/deposits.py
+++ b/test_generators/operations/deposits.py
@ -77,7 +77,7 @@ def build_deposit_for_index(initial_validator_count: int, index: int) -> Tuple[s
        keys.pubkeys[index],
        keys.withdrawal_creds[index],
        keys.privkeys[index],
-        spec.MAX_DEPOSIT_AMOUNT,
+        spec.MAX_EFFECTIVE_BALANCE,
    )

    state.latest_eth1_data.deposit_root = get_merkle_root(tuple(deposit_data_leaves))
--- a/test_generators/operations/genesis.py
+++ b/test_generators/operations/genesis.py
@ -26,7 +26,7 @@ def create_deposits(pubkeys: List[spec.BLSPubkey], withdrawal_cred: List[spec.By
        spec.DepositData(
            pubkey=pubkeys[i],
            withdrawal_credentials=spec.BLS_WITHDRAWAL_PREFIX_BYTE + withdrawal_cred[i][1:],
-            amount=spec.MAX_DEPOSIT_AMOUNT,
+            amount=spec.MAX_EFFECTIVE_BALANCE,
            proof_of_possession=proof_of_possession,
        ) for i in range(len(pubkeys))
    ]
--- a/test_libs/config_helpers/requirements.txt
+++ b/test_libs/config_helpers/requirements.txt
@ -0,0 +1 @@
+ruamel.yaml==0.15.87
--- a/test_libs/config_helpers/setup.py
+++ b/test_libs/config_helpers/setup.py
@ -1,20 +1,9 @@
-from setuptools import setup, find_packages
-
-
-deps = {
-    'preset_loader': [
-        "ruamel.yaml==0.15.87",
-    ],
-}
-
-deps['dev'] = (
-    deps['preset_loader']
-)
-
-install_requires = deps['preset_loader']
+from distutils.core import setup

 setup(
    name='config_helpers',
-    packages=find_packages(exclude=["tests", "tests.*"]),
-    install_requires=install_requires,
+    packages=['preset_loader'],
+    install_requires=[
+        "ruamel.yaml==0.15.87"
+    ]
 )
--- a/test_libs/gen_helpers/gen_base/gen_typing.py
+++ b/test_libs/gen_helpers/gen_base/gen_typing.py
@ -1,4 +1,10 @@
-from typing import Callable, Dict, Tuple, Any
+from typing import (
+    Any,
+    Callable,
+    Dict,
+    Tuple,
+)
+

 TestCase = Dict[str, Any]
 TestSuite = Dict[str, Any]
--- a/test_libs/gen_helpers/requirements.txt
+++ b/test_libs/gen_helpers/requirements.txt
@ -0,0 +1,2 @@
+ruamel.yaml==0.15.87
+eth-utils==1.4.1
--- a/test_libs/gen_helpers/setup.py
+++ b/test_libs/gen_helpers/setup.py
@ -1,21 +1,10 @@
-from setuptools import setup, find_packages
-
-
-deps = {
-    'gen_base': [
-        "ruamel.yaml==0.15.87",
-        "eth-utils==1.4.1",
-    ],
-}
-
-deps['dev'] = (
-    deps['gen_base']
-)
-
-install_requires = deps['gen_base']
+from distutils.core import setup

 setup(
    name='gen_helpers',
-    packages=find_packages(exclude=["tests", "tests.*"]),
-    install_requires=install_requires,
+    packages=['gen_base'],
+    install_requires=[
+        "ruamel.yaml==0.15.87",
+        "eth-utils==1.4.1"
+    ]
 )
--- a/test_libs/pyspec/README.md
+++ b/test_libs/pyspec/README.md
@ -1,11 +1,11 @@
-# ETH 2.0 PySpec
+# Eth 2.0 Executable Python Spec (PySpec)

-The Python executable spec is built from the ETH 2.0 specification, 
+The executable Python spec is built from the Eth 2.0 specification, 
 complemented with the necessary helper functions for hashing, BLS, and more.

 With this executable spec,
 test-generators can easily create test-vectors for client implementations,
- and the spec itself can be verified to be consistent and coherent, through sanity tests implemented with pytest.
+ and the spec itself can be verified to be consistent and coherent through sanity tests implemented with pytest.


 ## Building
@ -14,12 +14,12 @@ All the dynamic parts of the spec can be build at once with `make pyspec`.

 Alternatively, you can build a sub-set of the pyspec: `make phase0`.

-Or, to build a single file, specify the path, e.g. `make test_libs/pyspec/eth2spec/phase0/spec.py`
+Or, to build a single file, specify the path, e.g. `make test_libs/pyspec/eth2spec/phase0/spec.py`.


 ## Py-tests

-After building, you can install the dependencies for running the `pyspec` tests with `make install_test`
+After building, you can install the dependencies for running the `pyspec` tests with `make install_test`.

 These tests are not intended for client-consumption.
 These tests are sanity tests, to verify if the spec itself is consistent.
@ -28,7 +28,7 @@ These tests are sanity tests, to verify if the spec itself is consistent.

 #### Automated

-Run `make test` from the root of the spec repository.
+Run `make test` from the root of the specs repository.

 #### Manual

@ -38,9 +38,9 @@ Install dependencies:
 ```bash
 python3 -m venv venv
 . venv/bin/activate
-pip3 install -e .[dev]
+pip3 install -r requirements-testing.txt
 ```
-Note: make sure to run `make -B pyspec` from the root of the specs repository,
+*Note*: Make sure to run `make -B pyspec` from the root of the specs repository,
 to build the parts of the pyspec module derived from the markdown specs.
 The `-B` flag may be helpful to force-overwrite the `pyspec` output after you made a change to the markdown source files.

@ -58,4 +58,4 @@ The pyspec is not a replacement.

 ## License

-Same as the spec itself, see [LICENSE](../../LICENSE) file in spec repository root.
+Same as the spec itself; see [LICENSE](../../LICENSE) file in the specs repository root.
--- a/test_libs/pyspec/eth2spec/utils/minimal_ssz.py
+++ b/test_libs/pyspec/eth2spec/utils/minimal_ssz.py
@ -3,7 +3,7 @@ from typing import Any
 from .hash_function import hash

 BYTES_PER_CHUNK = 32
-BYTES_PER_LENGTH_PREFIX = 4
+BYTES_PER_LENGTH_OFFSET = 4
 ZERO_CHUNK = b'\x00' * BYTES_PER_CHUNK


@ -111,19 +111,34 @@ def coerce_to_bytes(x):
        raise Exception("Expecting bytes")


-def encode_bytes(value):
-    serialized_bytes = coerce_to_bytes(value)
-    assert len(serialized_bytes) < 2 ** (8 * BYTES_PER_LENGTH_PREFIX)
-    serialized_length = len(serialized_bytes).to_bytes(BYTES_PER_LENGTH_PREFIX, 'little')
-    return serialized_length + serialized_bytes
+def encode_series(values, types):
+    # Recursively serialize
+    parts = [(is_constant_sized(types[i]), serialize_value(values[i], types[i])) for i in range(len(values))]

+    # Compute and check lengths
+    fixed_lengths = [len(serialized) if constant_size else BYTES_PER_LENGTH_OFFSET
+                     for (constant_size, serialized) in parts]
+    variable_lengths = [len(serialized) if not constant_size else 0
+                        for (constant_size, serialized) in parts]

-def encode_variable_size_container(values, types):
-    return encode_bytes(encode_fixed_size_container(values, types))
+    # Check if integer is not out of bounds (Python)
+    assert sum(fixed_lengths + variable_lengths) < 2 ** (BYTES_PER_LENGTH_OFFSET * 8)

+    # Interleave offsets of variable-size parts with fixed-size parts.
+    # Avoid quadratic complexity in calculation of offsets.
+    offset = sum(fixed_lengths)
+    variable_parts = []
+    fixed_parts = []
+    for (constant_size, serialized) in parts:
+        if constant_size:
+            fixed_parts.append(serialized)
+        else:
+            fixed_parts.append(offset.to_bytes(BYTES_PER_LENGTH_OFFSET, 'little'))
+            variable_parts.append(serialized)
+            offset += len(serialized)

-def encode_fixed_size_container(values, types):
-    return b''.join([serialize_value(v, typ) for (v, typ) in zip(values, types)])
+    # Return the concatenation of the fixed-size parts (offsets interleaved) with the variable-size parts
+    return b"".join(fixed_parts + variable_parts)


 def serialize_value(value, typ=None):
@ -142,18 +157,13 @@ def serialize_value(value, typ=None):
    elif isinstance(typ, list) and len(typ) == 2:
        # (regardless of element type, sanity-check if the length reported in the vector type matches the value length)
        assert len(value) == typ[1]
-        # If value is fixed-size (i.e. element type is fixed-size):
-        if is_constant_sized(typ):
-            return encode_fixed_size_container(value, [typ[0]] * len(value))
-        # If value is variable-size (i.e. element type is variable-size)
-        else:
-            return encode_variable_size_container(value, [typ[0]] * len(value))
-    # "bytes" (variable size)
-    elif isinstance(typ, str) and typ == 'bytes':
-        return encode_bytes(value)
+        return encode_series(value, [typ[0]] * len(value))
    # List
    elif isinstance(typ, list) and len(typ) == 1:
-        return encode_variable_size_container(value, [typ[0]] * len(value))
+        return encode_series(value, [typ[0]] * len(value))
+    # "bytes" (variable size)
+    elif isinstance(typ, str) and typ == 'bytes':
+        return coerce_to_bytes(value)
    # "bytesN" (fixed size)
    elif isinstance(typ, str) and len(typ) > 5 and typ[:5] == 'bytes':
        assert len(value) == int(typ[5:]), (value, int(typ[5:]))
@ -162,10 +172,7 @@ def serialize_value(value, typ=None):
    elif hasattr(typ, 'fields'):
        values = [getattr(value, field) for field in typ.fields.keys()]
        types = list(typ.fields.values())
-        if is_constant_sized(typ):
-            return encode_fixed_size_container(values, types)
-        else:
-            return encode_variable_size_container(values, types)
+        return encode_series(values, types)
    else:
        print(value, typ)
        raise Exception("Type not recognized")
--- a/test_libs/pyspec/requirements-testing.txt
+++ b/test_libs/pyspec/requirements-testing.txt
@ -0,0 +1,3 @@
+-r requirements.txt
+pytest>=3.6,<3.7
+../config_helpers
--- a/test_libs/pyspec/requirements.txt
+++ b/test_libs/pyspec/requirements.txt
@ -0,0 +1,4 @@
+eth-utils>=1.3.0,<2
+eth-typing>=2.1.0,<3.0.0
+pycryptodome==3.7.3
+py_ecc>=1.6.0
--- a/test_libs/pyspec/setup.py
+++ b/test_libs/pyspec/setup.py
@ -1,28 +1,13 @@
 from setuptools import setup, find_packages

-
-deps = {
-    'pyspec': [
+setup(
+    name='pyspec',
+    packages=find_packages(),
+    tests_require=["pytest"],
+    install_requires=[
        "eth-utils>=1.3.0,<2",
        "eth-typing>=2.1.0,<3.0.0",
        "pycryptodome==3.7.3",
        "py_ecc>=1.6.0",
-    ],
-    'test': [
-        "pytest>=3.6,<3.7",
-    ],
-}
-
-deps['dev'] = (
-    deps['pyspec'] +
-    deps['test']
-)
-
-install_requires = deps['pyspec']
-
-setup(
-    name='pyspec',
-    packages=find_packages(exclude=["tests", "tests.*"]),
-    install_requires=install_requires,
-    extras_require=deps,
+    ]
 )
--- a/test_libs/pyspec/tests/block_processing/test_process_attestation.py
+++ b/test_libs/pyspec/tests/block_processing/test_process_attestation.py
@ -38,8 +38,7 @@ def run_attestation_processing(state, attestation, valid=True):
    process_attestation(post_state, attestation)

    current_epoch = get_current_epoch(state)
-    target_epoch = slot_to_epoch(attestation.data.slot)
-    if target_epoch == current_epoch:
+    if attestation.data.target_epoch == current_epoch:
        assert len(post_state.current_epoch_attestations) == len(state.current_epoch_attestations) + 1
    else:
        assert len(post_state.previous_epoch_attestations) == len(state.previous_epoch_attestations) + 1
--- a/test_libs/pyspec/tests/block_processing/test_process_attester_slashing.py
+++ b/test_libs/pyspec/tests/block_processing/test_process_attester_slashing.py
@ -65,7 +65,7 @@ def test_success_surround(state):

    # set attestion1 to surround attestation 2
    attester_slashing.attestation_1.data.source_epoch = attester_slashing.attestation_2.data.source_epoch - 1
-    attester_slashing.attestation_1.data.slot = attester_slashing.attestation_2.data.slot + spec.SLOTS_PER_EPOCH
+    attester_slashing.attestation_1.data.target_epoch = attester_slashing.attestation_2.data.target_epoch + 1

    pre_state, post_state = run_attester_slashing_processing(state, attester_slashing)

@ -85,7 +85,7 @@ def test_same_data(state):
 def test_no_double_or_surround(state):
    attester_slashing = get_valid_attester_slashing(state)

-    attester_slashing.attestation_1.data.slot += spec.SLOTS_PER_EPOCH
+    attester_slashing.attestation_1.data.target_epoch += 1

    pre_state, post_state = run_attester_slashing_processing(state, attester_slashing, False)

--- a/test_libs/pyspec/tests/block_processing_phase1/phase1_test_process_randao_key_reveal.py
+++ b/test_libs/pyspec/tests/block_processing_phase1/phase1_test_process_randao_key_reveal.py
@ -0,0 +1,109 @@
+from copy import deepcopy
+import pytest
+
+import eth2spec.phase1.spec as spec
+from eth2spec.phase1.spec import (
+    get_current_epoch,
+    process_randao_key_reveal,
+    RANDAO_PENALTY_EPOCHS,
+    CUSTODY_PERIOD_TO_RANDAO_PADDING,
+    RANDAO_PENALTY_MAX_FUTURE_EPOCHS,
+)
+from tests.helpers_phase1 import (
+    get_valid_randao_key_reveal,
+)
+
+mark entire file as 'randao_key_reveals'
+pytestmark = pytest.mark.randao_key_reveals
+
+
+def run_randao_key_reveal_processing(state, randao_key_reveal, valid=True):
+    """
+    Run ``process_randao_key_reveal`` returning the pre and post state.
+    If ``valid == False``, run expecting ``AssertionError``
+    """
+    post_state = deepcopy(state)
+
+    if not valid:
+        with pytest.raises(AssertionError):
+            process_randao_key_reveal(post_state, randao_key_reveal)
+        return state, None
+
+    process_randao_key_reveal(post_state, randao_key_reveal)
+
+    slashed_validator = post_state.validator_registry[randao_key_reveal.revealed_index]
+
+    if randao_key_reveal.epoch >= get_current_epoch(state) + CUSTODY_PERIOD_TO_RANDAO_PADDING:
+        assert slashed_validator.slashed
+        assert slashed_validator.exit_epoch < spec.FAR_FUTURE_EPOCH
+        assert slashed_validator.withdrawable_epoch < spec.FAR_FUTURE_EPOCH
+    # lost whistleblower reward
+    # FIXME: Currently broken because get_base_reward in genesis epoch is 0
+    assert (
+        post_state.balances[randao_key_reveal.revealed_index] <
+        state.balances[randao_key_reveal.revealed_index]
+    )
+
+    return state, post_state
+
+
+def test_success(state):
+    randao_key_reveal = get_valid_randao_key_reveal(state)
+
+    pre_state, post_state = run_randao_key_reveal_processing(state, randao_key_reveal)
+
+    return pre_state, randao_key_reveal, post_state
+
+
+def test_reveal_from_current_epoch(state):
+    randao_key_reveal = get_valid_randao_key_reveal(state, get_current_epoch(state))
+
+    pre_state, post_state = run_randao_key_reveal_processing(state, randao_key_reveal, False)
+
+    return pre_state, randao_key_reveal, post_state
+
+# Not currently possible as we are testing at epoch 0
+#
+#def test_reveal_from_past_epoch(state):
+#    randao_key_reveal = get_valid_randao_key_reveal(state, get_current_epoch(state) - 1)
+#
+#    pre_state, post_state = run_randao_key_reveal_processing(state, randao_key_reveal, False)
+#
+#    return pre_state, randao_key_reveal, post_state
+
+def test_reveal_with_custody_padding(state):
+    randao_key_reveal = get_valid_randao_key_reveal(state, get_current_epoch(state) + CUSTODY_PERIOD_TO_RANDAO_PADDING)
+    pre_state, post_state = run_randao_key_reveal_processing(state, randao_key_reveal, True)
+
+    return pre_state, randao_key_reveal, post_state
+
+def test_reveal_with_custody_padding_minus_one(state):
+    randao_key_reveal = get_valid_randao_key_reveal(state, get_current_epoch(state) + CUSTODY_PERIOD_TO_RANDAO_PADDING - 1)
+    pre_state, post_state = run_randao_key_reveal_processing(state, randao_key_reveal, True)
+
+    return pre_state, randao_key_reveal, post_state
+
+def test_double_reveal(state):
+    
+    randao_key_reveal1 = get_valid_randao_key_reveal(state, get_current_epoch(state) + RANDAO_PENALTY_EPOCHS + 1)
+    pre_state, intermediate_state = run_randao_key_reveal_processing(state, randao_key_reveal1)
+    
+    randao_key_reveal2 = get_valid_randao_key_reveal(intermediate_state, get_current_epoch(pre_state) + RANDAO_PENALTY_EPOCHS + 1)
+    intermediate_state_, post_state = run_randao_key_reveal_processing(intermediate_state, randao_key_reveal2, False)
+
+    return pre_state, [randao_key_reveal1, randao_key_reveal2], post_state
+
+def test_revealer_is_slashed(state):
+    randao_key_reveal = get_valid_randao_key_reveal(state, get_current_epoch(state))
+    state.validator_registry[randao_key_reveal.revealed_index].slashed = True
+
+    pre_state, post_state = run_randao_key_reveal_processing(state, randao_key_reveal, False)
+
+    return pre_state, randao_key_reveal, post_state
+
+def test_far_future_epoch(state):
+    randao_key_reveal = get_valid_randao_key_reveal(state, get_current_epoch(state) + RANDAO_PENALTY_MAX_FUTURE_EPOCHS)
+
+    pre_state, post_state = run_randao_key_reveal_processing(state, randao_key_reveal, False)
+
+    return pre_state, randao_key_reveal, post_state
--- a/test_libs/pyspec/tests/epoch_processing/test_process_crosslinks.py
+++ b/test_libs/pyspec/tests/epoch_processing/test_process_crosslinks.py
@ -15,7 +15,7 @@ from tests.helpers import (
    add_attestation_to_state,
    build_empty_block_for_next_slot,
    fill_aggregate_attestation,
-    get_crosslink_committee_for_attestation,
+    get_crosslink_committee,
    get_valid_attestation,
    next_epoch,
    next_slot,
@ -88,7 +88,7 @@ def test_single_crosslink_update_from_previous_epoch(state):
    assert post_state.previous_crosslinks[shard] != post_state.current_crosslinks[shard]
    assert pre_state.current_crosslinks[shard] != post_state.current_crosslinks[shard]
    # ensure rewarded
-    for index in get_crosslink_committee_for_attestation(state, attestation.data):
+    for index in get_crosslink_committee(state, attestation.data.target_epoch, attestation.data.shard):
        assert crosslink_deltas[0][index] > 0
        assert crosslink_deltas[1][index] == 0

@ -129,7 +129,7 @@ def test_double_late_crosslink(state):
    # ensure that the current crosslinks were not updated by the second attestation
    assert post_state.previous_crosslinks[shard] == post_state.current_crosslinks[shard]
    # ensure no reward, only penalties for the failed crosslink
-    for index in get_crosslink_committee_for_attestation(state, attestation_2.data):
+    for index in get_crosslink_committee(state, attestation_2.data.target_epoch, attestation_2.data.shard):
        assert crosslink_deltas[0][index] == 0
        assert crosslink_deltas[1][index] > 0

--- a/test_libs/pyspec/tests/epoch_processing/test_process_registry_updates.py
+++ b/test_libs/pyspec/tests/epoch_processing/test_process_registry_updates.py
@ -0,0 +1,67 @@
+from copy import deepcopy
+
+import pytest
+
+import eth2spec.phase0.spec as spec
+
+from eth2spec.phase0.spec import (
+    get_current_epoch,
+    is_active_validator,
+)
+from tests.helpers import (
+    next_epoch,
+)
+
+# mark entire file as 'state'
+pytestmark = pytest.mark.state
+
+
+def test_activation(state):
+    index = 0
+    assert is_active_validator(state.validator_registry[index], get_current_epoch(state))
+
+    # Mock a new deposit
+    state.validator_registry[index].activation_eligibility_epoch = spec.FAR_FUTURE_EPOCH
+    state.validator_registry[index].activation_epoch = spec.FAR_FUTURE_EPOCH
+    state.validator_registry[index].effective_balance = spec.MAX_EFFECTIVE_BALANCE
+    assert not is_active_validator(state.validator_registry[index], get_current_epoch(state))
+
+    pre_state = deepcopy(state)
+
+    blocks = []
+    for _ in range(spec.ACTIVATION_EXIT_DELAY + 1):
+        block = next_epoch(state)
+        blocks.append(block)
+
+    assert state.validator_registry[index].activation_eligibility_epoch != spec.FAR_FUTURE_EPOCH
+    assert state.validator_registry[index].activation_epoch != spec.FAR_FUTURE_EPOCH
+    assert is_active_validator(
+        state.validator_registry[index],
+        get_current_epoch(state),
+    )
+
+    return pre_state, blocks, state
+
+
+def test_ejection(state):
+    index = 0
+    assert is_active_validator(state.validator_registry[index], get_current_epoch(state))
+    assert state.validator_registry[index].exit_epoch == spec.FAR_FUTURE_EPOCH
+
+    # Mock an ejection
+    state.validator_registry[index].effective_balance = spec.EJECTION_BALANCE
+
+    pre_state = deepcopy(state)
+
+    blocks = []
+    for _ in range(spec.ACTIVATION_EXIT_DELAY + 1):
+        block = next_epoch(state)
+        blocks.append(block)
+
+    assert state.validator_registry[index].exit_epoch != spec.FAR_FUTURE_EPOCH
+    assert not is_active_validator(
+        state.validator_registry[index],
+        get_current_epoch(state),
+    )
+
+    return pre_state, blocks, state
--- a/test_libs/pyspec/tests/helpers.py
+++ b/test_libs/pyspec/tests/helpers.py
@ -29,7 +29,7 @@ from eth2spec.phase0.spec import (
    get_attesting_indices,
    get_block_root,
    get_block_root_at_slot,
-    get_crosslink_committees_at_slot,
+    get_crosslink_committee,
    get_current_epoch,
    get_domain,
    get_epoch_start_slot,
@ -174,11 +174,11 @@ def build_attestation_data(state, slot, shard):

    crosslinks = state.current_crosslinks if slot_to_epoch(slot) == get_current_epoch(state) else state.previous_crosslinks
    return AttestationData(
-        slot=slot,
        shard=shard,
        beacon_block_root=block_root,
        source_epoch=justified_epoch,
        source_root=justified_block_root,
+        target_epoch=slot_to_epoch(slot),
        target_root=epoch_boundary_root,
        crosslink_data_root=spec.ZERO_HASH,
        previous_crosslink_root=hash_tree_root(crosslinks[shard]),
@ -276,14 +276,6 @@ def get_valid_attester_slashing(state):
    )


-def get_crosslink_committee_for_attestation(state, attestation_data):
-    """
-    Return the crosslink committee corresponding to ``attestation_data``.
-    """
-    crosslink_committees = get_crosslink_committees_at_slot(state, attestation_data.slot)
-    return [committee for committee, shard in crosslink_committees if shard == attestation_data.shard][0]
-
-
 def get_valid_attestation(state, slot=None):
    if slot is None:
        slot = state.slot
@ -296,7 +288,7 @@ def get_valid_attestation(state, slot=None):

    attestation_data = build_attestation_data(state, slot, shard)

-    crosslink_committee = get_crosslink_committee_for_attestation(state, attestation_data)
+    crosslink_committee = get_crosslink_committee(state, attestation_data.target_epoch, attestation_data.shard)

    committee_size = len(crosslink_committee)
    bitfield_length = (committee_size + 7) // 8
@ -383,13 +375,13 @@ def get_attestation_signature(state, attestation_data, privkey, custody_bit=0b0)
        domain=get_domain(
            state=state,
            domain_type=spec.DOMAIN_ATTESTATION,
-            message_epoch=slot_to_epoch(attestation_data.slot),
+            message_epoch=attestation_data.target_epoch,
        )
    )


 def fill_aggregate_attestation(state, attestation):
-    crosslink_committee = get_crosslink_committee_for_attestation(state, attestation.data)
+    crosslink_committee = get_crosslink_committee(state, attestation.data.target_epoch, attestation.data.shard)
    for i in range(len(crosslink_committee)):
        attestation.aggregation_bitfield = set_bitfield_bit(attestation.aggregation_bitfield, i)

@ -402,11 +394,29 @@ def add_attestation_to_state(state, attestation, slot):


 def next_slot(state):
+    """
+    Transition to the next slot via an empty block.
+    Return the empty block that triggered the transition.
+    """
    block = build_empty_block_for_next_slot(state)
    state_transition(state, block)
+    return block


 def next_epoch(state):
+    """
+    Transition to the start slot of the next epoch via an empty block.
+    Return the empty block that triggered the transition.
+    """
    block = build_empty_block_for_next_slot(state)
    block.slot += spec.SLOTS_PER_EPOCH - (state.slot % spec.SLOTS_PER_EPOCH)
    state_transition(state, block)
+    return block
+
+
+def get_state_root(state, slot) -> bytes:
+    """
+    Return the state root at a recent ``slot``.
+    """
+    assert slot < state.slot <= slot + spec.SLOTS_PER_HISTORICAL_ROOT
+    return state.latest_state_roots[slot % spec.SLOTS_PER_HISTORICAL_ROOT]
--- a/test_libs/pyspec/tests/helpers_phase1.py
+++ b/test_libs/pyspec/tests/helpers_phase1.py
@ -0,0 +1,50 @@
+from py_ecc import bls
+
+import eth2spec.phase1.spec as spec
+from eth2spec.phase0.spec import (
+    # constants
+    ZERO_HASH,
+    CUSTODY_PERIOD_TO_RANDAO_PADDING,
+    # SSZ
+    RandaoKeyReveal,
+    # functions
+    get_active_validator_indices,
+    get_current_epoch,
+    get_domain,
+    hash_tree_root,
+)
+
+def get_valid_randao_key_reveal(state, epoch=None):
+    current_epoch = get_current_epoch(state)
+    revealed_index = get_active_validator_indices(state, current_epoch)[-1]
+    masker_index = get_active_validator_indices(state, current_epoch)[0]
+
+    if epoch is None:
+        epoch = current_epoch + CUSTODY_PERIOD_TO_RANDAO_PADDING
+
+    reveal = bls.sign(
+        message_hash=hash_tree_root(epoch),
+        privkey=pubkey_to_privkey[state.validator_registry[revealed_index].pubkey],
+        domain=get_domain(
+            state=state,
+            domain_type=spec.DOMAIN_RANDAO,
+            message_epoch=epoch,
+        ),
+    )
+    mask = bls.sign(
+        message_hash=hash_tree_root(epoch),
+        privkey=pubkey_to_privkey[state.validator_registry[masker_index].pubkey],
+        domain=get_domain(
+            state=state,
+            domain_type=spec.DOMAIN_RANDAO,
+            message_epoch=epoch,
+        ),
+    )
+
+    return RandaoKeyReveal(
+        revealed_index=revealed_index,
+        epoch=epoch,
+        reveal=reveal,
+        masker_index=masker_index,
+        mask=mask,
+    )
--- a/test_libs/pyspec/tests/test_sanity.py
+++ b/test_libs/pyspec/tests/test_sanity.py
@ -9,6 +9,7 @@ from eth2spec.utils.minimal_ssz import signing_root
 from eth2spec.phase0.spec import (
    # constants
    ZERO_HASH,
+    SLOTS_PER_HISTORICAL_ROOT,
    # SSZ
    Deposit,
    Transfer,
@ -17,7 +18,6 @@ from eth2spec.phase0.spec import (
    get_active_validator_indices,
    get_beacon_proposer_index,
    get_block_root_at_slot,
-    get_state_root,
    get_current_epoch,
    get_domain,
    advance_slot,
@ -38,6 +38,7 @@ from .helpers import (
    build_deposit_data,
    build_empty_block_for_next_slot,
    fill_aggregate_attestation,
+    get_state_root,
    get_valid_attestation,
    get_valid_attester_slashing,
    get_valid_proposer_slashing,
--- a/test_libs/setup.py
+++ b/test_libs/setup.py
@ -1,29 +0,0 @@
-from setuptools import setup, find_packages
-
-
-deps = {
-    'pyspec': [
-        "eth-utils>=1.3.0,<2",
-        "eth-typing>=2.1.0,<3.0.0",
-        "pycryptodome==3.7.3",
-        "py_ecc>=1.6.0",
-    ],
-    'test': [
-        "pytest>=3.6,<3.7",
-    ],
-}
-
-deps['dev'] = (
-    deps['pyspec'] +
-    deps['test']
-)
-
-install_requires = deps['pyspec']
-
-
-setup(
-    name='pyspec',
-    packages=find_packages(exclude=["tests", "tests.*"]),
-    install_requires=install_requires,
-    extras_require=deps,
-)