Added a few things
This commit is contained in:
Vitalik Buterin
Danny Ryan
parent
88aeba09f6
commit
f6be6b2b8a
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@ -12,8 +12,13 @@
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- [Configuration](#configuration)
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- [Misc](#misc)
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- [Containers](#containers)
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- [Helpers](#helpers)
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- [Beacon Chain Changes](#beacon-chain-changes)
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- [New state variables](#new-state-variables)
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- [Attestation processing](#attestation-processing)
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- [Epoch transition](#epoch-transition)
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- [Fraud proofs](#fraud-proofs)
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- [Honest persistent committee member behavior](#honest-persistent-committee-member-behavior)
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<!-- /TOC -->
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@ -30,7 +35,8 @@ This document describes the shard transition function (data layer only) and the
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| `MAX_SHARDS` | `2**10` (= 1024) |
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| `ACTIVE_SHARDS` | `2**6` (= 64) |
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| `SHARD_ROOT_HISTORY_LENGTH` | `2**15` (= 32,768) |
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| `MAX_CATCHUP` | `2**3` (= 8) |
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| `MAX_CATCHUP` | `2**5` (= 32) |
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| `ONLINE_PERIOD` | `2**3` (= 8) |
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## Containers
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@ -40,8 +46,6 @@ This document describes the shard transition function (data layer only) and the
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class AttestationData(Container):
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# Slot
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slot: Slot
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# Shard
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shard: shard
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# LMD GHOST vote
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beacon_block_root: Hash
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# FFG vote
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@ -51,6 +55,8 @@ class AttestationData(Container):
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shard_data_roots: List[Hash, MAX_CATCHUP]
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# Intermediate state roots
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shard_state_roots: List[Hash, MAX_CATCHUP]
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# Index
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index: uint64
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```
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### `Attestation`
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@ -63,13 +69,31 @@ class Attestation(Container):
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signature: BLSSignature
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```
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## Helpers
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### `get_online_validators`
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```python
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def get_online_indices(state: BeaconState) -> Set[ValidatorIndex]:
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active_validators = get_active_validator_indices(state, get_current_epoch(state))
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return set([i for i in active_validators if state.online_countdown[i] != 0])
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```
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### `get_shard_state_root`
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```python
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def get_shard_state_root(state: BeaconState, shard: Shard) -> Hash:
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return state.shard_state_roots[shard][-1]
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```
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## Beacon Chain Changes
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### New state variables
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```
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shard_state_roots: Vector[Hash, MAX_SHARDS]
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shard_state_roots: Vector[List[Hash, MAX_CATCHUP], MAX_SHARDS]
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shard_next_slot: Vector[Slot, MAX_SHARDS]
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online_countdown: Bytes[VALIDATOR_REGISTRY_LIMIT]
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```
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### Attestation processing
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@ -77,38 +101,43 @@ class Attestation(Container):
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```python
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def process_attestation(state: BeaconState, attestation: Attestation) -> None:
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data = attestation.data
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assert shard < ACTIVE_SHARDS
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assert data.index < ACTIVE_SHARDS
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shard = (data.index + get_start_shard(state, data.slot)) % ACTIVE_SHARDS
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# Signature check
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committee = get_crosslink_committee(state, get_current_epoch(state), data.shard)
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committee = get_crosslink_committee(state, get_current_epoch(state), shard)
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for bits in attestation.custody_bits + [attestation.aggregation_bits]:
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assert bits == len(committee)
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# Check signature
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assert is_valid_indexed_attestation(state, get_indexed_attestation(state, attestation))
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# Get attesting indices
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attesting_indices = get_attesting_indices(state, attestation.data, attestation.aggregation_bits)
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# Type 1: on-time attestations
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if data.custody_bits != []:
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# Correct start slot
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assert data.slot == state.shard_next_slot[data.shard]
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assert data.slot == state.shard_next_slot[shard]
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# Correct data root count
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assert len(data.shard_data_roots) == len(attestation.custody_bits) == len(data.shard_state_roots) == min(state.slot - data.slot, MAX_CATCHUP)
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# Correct parent block root
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assert data.beacon_block_root == get_block_root_at_slot(state, state.slot - 1)
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# Apply
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online_indices = get_online_indices(state)
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attesting_indices = get_attesting_indices(state, attestation.data, attestation.aggregation_bits).intersection(get_online_indices)
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if get_total_balance(state, attesting_indices) * 3 >= get_total_balance(state, online_indices) * 2:
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state.shard_state_roots[data.shard] = data.shard_state_roots[-1]
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state.shard_next_slot[data.shard] += len(data.shard_data_roots)
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if get_total_balance(state, online_indices.intersection(attesting_indices)) * 3 >= get_total_balance(state, online_indices) * 2:
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state.shard_state_roots[shard] = data.shard_state_roots
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state.shard_next_slot[shard] += len(data.shard_data_roots)
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# Type 2: delayed attestations
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else:
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assert slot_to_epoch(data.slot) in (get_current_epoch(state), get_previous_epoch(state))
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assert len(data.shard_data_roots) == len(data.intermediate_state_roots) == 0
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for index in attesting_indices:
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online_countdown[index] = ONLINE_PERIOD
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pending_attestation = PendingAttestation(
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slot=data.slot,
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shard=data.shard,
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shard=shard,
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aggregation_bits=attestation.aggregation_bits,
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inclusion_delay=state.slot - attestation_slot,
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proposer_index=get_beacon_proposer_index(state),
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@ -122,12 +151,20 @@ def process_attestation(state: BeaconState, attestation: Attestation) -> None:
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state.previous_epoch_attestations.append(pending_attestation)
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```
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### Epoch transition
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```python
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for index in range(len(state.validators)):
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if state.online_countdown[index] != 0:
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state.online_countdown[index] = state.online_countdown[index] - 1
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```
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### Fraud proofs
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TODO. The intent is to have a single universal fraud proof type, which contains (i) an on-time attestation on shard `s` signing a set of `data_roots`, (ii) an index `i` of a particular data root to focus on, (iii) the full contents of the i'th data, (iii) a Merkle proof to the `shard_state_roots` in the parent block the attestation is referencing, and which then verifies that one of the two conditions is false:
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* `custody_bits[i][j] != generate_custody_bit(subkey, block_contents)` for any `j`
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* `execute_state_transition(slot, shard, attestation.shard_state_roots[i-1], parent.shard_state_roots, block_contents) != shard_state_roots[i]` (if `i=0` then instead use `parent.shard_state_roots[s]`)
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* `execute_state_transition(slot, shard, attestation.shard_state_roots[i-1], parent.shard_state_roots, block_contents) != shard_state_roots[i]` (if `i=0` then instead use `parent.shard_state_roots[s][-1]`)
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For phase 1, we will use a simple state transition function:
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@ -135,7 +172,7 @@ For phase 1, we will use a simple state transition function:
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* Check that `bls_verify(get_shard_proposer(state, slot, shard), hash_tree_root(data[-96:]), BLSSignature(data[-96:]), BLOCK_SIGNATURE_DOMAIN)`
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* Output the new state root: `hash_tree_root(prev_state_root, other_prev_state_roots, data)`
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### Honest persistent committee member behavior
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## Honest persistent committee member behavior
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Suppose you are a persistent committee member on shard `i` at slot `s`. Suppose `state.shard_next_slots[i] = s-1` ("the happy case"). In this case, you look for a valid proposal that satisfies the checks in the state transition function above, and if you see such a proposal `data` with post-state `post_state`, make an attestation with `shard_data_roots = [hash_tree_root(data)]` and `shard_state_roots = [post_state]`. If you do not find such a proposal, make an attestation using the "default empty proposal", `data = prev_state_root + b'\x00' * 96`.
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