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cleanup old docs about transition-full sharding

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specs/phase1/shard-fork-choice.md
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# Ethereum 2.0 Phase 1 -- Beacon Chain + Shard Chain Fork Choice
**Notice**: This document is a work-in-progress for researchers and implementers.
## Table of contents
<!-- START doctoc generated TOC please keep comment here to allow auto update -->
<!-- DON'T EDIT THIS SECTION, INSTEAD RE-RUN doctoc TO UPDATE -->
- [Introduction](#introduction)
- [Fork choice](#fork-choice)
- [Helpers](#helpers)
- [`get_forkchoice_shard_store`](#get_forkchoice_shard_store)
- [`get_shard_latest_attesting_balance`](#get_shard_latest_attesting_balance)
- [`get_shard_head`](#get_shard_head)
- [`get_shard_ancestor`](#get_shard_ancestor)
- [`get_pending_shard_blocks`](#get_pending_shard_blocks)
- [Handlers](#handlers)
- [`on_shard_block`](#on_shard_block)
<!-- END doctoc generated TOC please keep comment here to allow auto update -->
## Introduction
This document is the shard chain fork choice spec for part of Ethereum 2.0 Phase 1. It assumes the [beacon chain fork choice spec](./fork-choice.md).
## Fork choice
### Helpers
#### `get_forkchoice_shard_store`
```python
def get_forkchoice_shard_store(anchor_state: BeaconState, shard: Shard) -> ShardStore:
return ShardStore(
shard=shard,
signed_blocks={
anchor_state.shard_states[shard].latest_block_root: SignedShardBlock(
message=ShardBlock(slot=compute_previous_slot(anchor_state.slot), shard=shard)
)
},
block_states={anchor_state.shard_states[shard].latest_block_root: anchor_state.copy().shard_states[shard]},
)
```
#### `get_shard_latest_attesting_balance`
```python
def get_shard_latest_attesting_balance(store: Store, shard: Shard, root: Root) -> Gwei:
shard_store = store.shard_stores[shard]
state = store.checkpoint_states[store.justified_checkpoint]
active_indices = get_active_validator_indices(state, get_current_epoch(state))
return Gwei(sum(
state.validators[i].effective_balance for i in active_indices
if (
i in shard_store.latest_messages
# TODO: check the latest message logic: currently, validator's previous vote of another shard
# would be ignored once their newer vote is accepted. Check if it makes sense.
and get_shard_ancestor(
store,
shard,
shard_store.latest_messages[i].root,
shard_store.signed_blocks[root].message.slot,
) == root
)
))
```
#### `get_shard_head`
```python
def get_shard_head(store: Store, shard: Shard) -> Root:
# Execute the LMD-GHOST fork choice
"""
Execute the LMD-GHOST fork choice.
"""
shard_store = store.shard_stores[shard]
beacon_head_root = get_head(store)
shard_head_state = store.block_states[beacon_head_root].shard_states[shard]
shard_head_root = shard_head_state.latest_block_root
shard_blocks = {
root: signed_shard_block.message for root, signed_shard_block in shard_store.signed_blocks.items()
if signed_shard_block.message.slot > shard_head_state.slot
}
while True:
# Find the valid child block roots
children = [
root for root, shard_block in shard_blocks.items()
if shard_block.shard_parent_root == shard_head_root
]
if len(children) == 0:
return shard_head_root
# Sort by latest attesting balance with ties broken lexicographically
shard_head_root = max(
children, key=lambda root: (get_shard_latest_attesting_balance(store, shard, root), root)
)
```
#### `get_shard_ancestor`
```python
def get_shard_ancestor(store: Store, shard: Shard, root: Root, slot: Slot) -> Root:
shard_store = store.shard_stores[shard]
block = shard_store.signed_blocks[root].message
if block.slot > slot:
return get_shard_ancestor(store, shard, block.shard_parent_root, slot)
elif block.slot == slot:
return root
else:
# root is older than queried slot, thus a skip slot. Return most recent root prior to slot
return root
```
#### `get_pending_shard_blocks`
```python
def get_pending_shard_blocks(store: Store, shard: Shard) -> Sequence[SignedShardBlock]:
"""
Return the canonical shard block branch that has not yet been crosslinked.
"""
shard_store = store.shard_stores[shard]
beacon_head_root = get_head(store)
beacon_head_state = store.block_states[beacon_head_root]
latest_shard_block_root = beacon_head_state.shard_states[shard].latest_block_root
shard_head_root = get_shard_head(store, shard)
root = shard_head_root
signed_shard_blocks = []
while root != latest_shard_block_root:
signed_shard_block = shard_store.signed_blocks[root]
signed_shard_blocks.append(signed_shard_block)
root = signed_shard_block.message.shard_parent_root
signed_shard_blocks.reverse()
return signed_shard_blocks
```
### Handlers
#### `on_shard_block`
```python
def on_shard_block(store: Store, signed_shard_block: SignedShardBlock) -> None:
shard_block = signed_shard_block.message
shard = shard_block.shard
shard_store = store.shard_stores[shard]
# Check shard parent exists
assert shard_block.shard_parent_root in shard_store.block_states
shard_parent_state = shard_store.block_states[shard_block.shard_parent_root]
# Check beacon parent exists
assert shard_block.beacon_parent_root in store.block_states
beacon_parent_state = store.block_states[shard_block.beacon_parent_root]
# Check that block is later than the finalized shard state slot (optimization to reduce calls to get_ancestor)
finalized_beacon_state = store.block_states[store.finalized_checkpoint.root]
finalized_shard_state = finalized_beacon_state.shard_states[shard]
assert shard_block.slot > finalized_shard_state.slot
# Check block is a descendant of the finalized block at the checkpoint finalized slot
finalized_slot = compute_start_slot_at_epoch(store.finalized_checkpoint.epoch)
assert (
get_ancestor(store, shard_block.beacon_parent_root, finalized_slot) == store.finalized_checkpoint.root
)
# Check the block is valid and compute the post-state
shard_state = shard_parent_state.copy()
shard_state_transition(shard_state, signed_shard_block, beacon_parent_state, validate_result=True)
# Add new block to the store
# Note: storing `SignedShardBlock` format for computing `ShardTransition.proposer_signature_aggregate`
shard_store.signed_blocks[hash_tree_root(shard_block)] = signed_shard_block
# Add new state for this block to the store
shard_store.block_states[hash_tree_root(shard_block)] = shard_state
```

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specs/phase1/shard-transition.md
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# Ethereum 2.0 Phase 1 -- Shard Transition and Fraud Proofs
**Notice**: This document is a work-in-progress for researchers and implementers.
## Table of contents
<!-- START doctoc generated TOC please keep comment here to allow auto update -->
<!-- DON'T EDIT THIS SECTION, INSTEAD RE-RUN doctoc TO UPDATE -->
- [Introduction](#introduction)
- [Helper functions](#helper-functions)
- [Shard block verification functions](#shard-block-verification-functions)
- [`verify_shard_block_message`](#verify_shard_block_message)
- [`verify_shard_block_signature`](#verify_shard_block_signature)
- [Shard state transition function](#shard-state-transition-function)
- [Fraud proofs](#fraud-proofs)
- [Verifying the proof](#verifying-the-proof)
<!-- END doctoc generated TOC please keep comment here to allow auto update -->
## Introduction
This document describes the shard transition function and fraud proofs as part of Phase 1 of Ethereum 2.0.
## Helper functions
### Shard block verification functions
#### `verify_shard_block_message`
```python
def verify_shard_block_message(beacon_parent_state: BeaconState,
shard_parent_state: ShardState,
block: ShardBlock) -> bool:
# Check `shard_parent_root` field
assert block.shard_parent_root == shard_parent_state.latest_block_root
# Check `beacon_parent_root` field
beacon_parent_block_header = beacon_parent_state.latest_block_header.copy()
if beacon_parent_block_header.state_root == Root():
beacon_parent_block_header.state_root = hash_tree_root(beacon_parent_state)
beacon_parent_root = hash_tree_root(beacon_parent_block_header)
assert block.beacon_parent_root == beacon_parent_root
# Check `slot` field
shard = block.shard
next_slot = Slot(block.slot + 1)
offset_slots = compute_offset_slots(get_latest_slot_for_shard(beacon_parent_state, shard), next_slot)
assert block.slot in offset_slots
# Check `proposer_index` field
assert block.proposer_index == get_shard_proposer_index(beacon_parent_state, block.slot, shard)
# Check `body` field
assert 0 < len(block.body) <= MAX_SHARD_BLOCK_SIZE
return True
```
#### `verify_shard_block_signature`
```python
def verify_shard_block_signature(beacon_parent_state: BeaconState,
signed_block: SignedShardBlock) -> bool:
proposer = beacon_parent_state.validators[signed_block.message.proposer_index]
domain = get_domain(beacon_parent_state, DOMAIN_SHARD_PROPOSAL, compute_epoch_at_slot(signed_block.message.slot))
signing_root = compute_signing_root(signed_block.message, domain)
return bls.Verify(proposer.pubkey, signing_root, signed_block.signature)
```
## Shard state transition function
The post-state corresponding to a pre-state `shard_state` and a signed block `signed_block` is defined as `shard_state_transition(shard_state, signed_block, beacon_parent_state)`, where `beacon_parent_state` is the parent beacon state of the `signed_block`. State transitions that trigger an unhandled exception (e.g. a failed `assert` or an out-of-range list access) are considered invalid. State transitions that cause a `uint64` overflow or underflow are also considered invalid.
```python
def shard_state_transition(shard_state: ShardState,
signed_block: SignedShardBlock,
beacon_parent_state: BeaconState,
validate_result: bool = True) -> None:
assert verify_shard_block_message(beacon_parent_state, shard_state, signed_block.message)
if validate_result:
assert verify_shard_block_signature(beacon_parent_state, signed_block)
process_shard_block(shard_state, signed_block.message)
```
```python
def process_shard_block(shard_state: ShardState,
block: ShardBlock) -> None:
"""
Update ``shard_state`` with shard ``block``.
"""
shard_state.slot = block.slot
prev_gasprice = shard_state.gasprice
shard_block_length = len(block.body)
shard_state.gasprice = compute_updated_gasprice(prev_gasprice, uint64(shard_block_length))
if shard_block_length != 0:
shard_state.latest_block_root = hash_tree_root(block)
```
## Fraud proofs
### Verifying the proof
TODO. The intent is to have a single universal fraud proof type, which contains the following parts:
1. An on-time attestation `attestation` on some shard `shard` signing a `transition: ShardTransition`
2. An index `offset_index` of a particular position to focus on
3. The `transition: ShardTransition` itself
4. The full body of the shard block `shard_block`
5. A Merkle proof to the `shard_states` in the parent block the attestation is referencing
6. The `subkey` to generate the custody bit
Call the following function to verify the proof:
```python
def is_valid_fraud_proof(beacon_state: BeaconState,
attestation: Attestation,
offset_index: uint64,
transition: ShardTransition,
block: ShardBlock,
subkey: BLSPubkey,
beacon_parent_block: BeaconBlock) -> bool:
# 1. Check if `custody_bits[offset_index][j] != generate_custody_bit(subkey, block_contents)` for any `j`.
custody_bits = attestation.custody_bits_blocks
for j in range(len(custody_bits[offset_index])):
if custody_bits[offset_index][j] != generate_custody_bit(subkey, block):
return True
# 2. Check if the shard state transition result is wrong between
# `transition.shard_states[offset_index - 1]` to `transition.shard_states[offset_index]`.
if offset_index == 0:
shard_states = beacon_parent_block.body.shard_transitions[attestation.data.shard].shard_states
shard_state = shard_states[len(shard_states) - 1]
else:
shard_state = transition.shard_states[offset_index - 1] # Not doing the actual state updates here.
process_shard_block(shard_state, block)
if shard_state != transition.shard_states[offset_index]:
return True
return False
```
```python
def generate_custody_bit(subkey: BLSPubkey, block: ShardBlock) -> bool:
# TODO
...
```