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Merge pull request #327 from ethereum/vbuterin-patch-18 

Keep randao mixes in the state
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Danny Ryan 2018-12-19 09:03:25 -06:00 committed by GitHub
parent 4077f4c558 36e26c86a3
commit 105e669391
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1 changed files with 12 additions and 13 deletions
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specs/core/0_beacon-chain.md
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@ -166,6 +166,7 @@ Unless otherwise indicated, code appearing in `this style` is to be interpreted
| `BLS_WITHDRAWAL_PREFIX_BYTE` | `0x00` | - |
| `MAX_CASPER_VOTES` | `2**10` (= 1,024) | votes |
| `LATEST_BLOCK_ROOTS_LENGTH` | `2**13` (= 8,192) | block roots |
| `LATEST_RANDAO_MIXES_LENGTH` | `2**13` (= 8,192) | randao mixes |
| `EMPTY_SIGNATURE` | `[bytes48(0), bytes48(0)]` | - |
* For the safety of crosslinks a minimum committee size of 111 is [recommended](https://vitalik.ca/files/Ithaca201807_Sharding.pdf). (Unbiasable randomness with a Verifiable Delay Function (VDF) will improve committee robustness and lower the safe minimum committee size.) The shuffling algorithm generally ensures (assuming sufficient validators) committee sizes at least `TARGET_COMMITTEE_SIZE // 2`.
@ -460,8 +461,7 @@ Unless otherwise indicated, code appearing in `this style` is to be interpreted
'validator_registry_delta_chain_tip': 'hash32', # For light clients to track deltas
# Randomness and committees
'randao_mix': 'hash32',
'next_seed': 'hash32',
'latest_randao_mixes': ['hash32'],
'shard_committees_at_slots': [[ShardCommittee]],
'persistent_committees': [['uint24']],
'persistent_committee_reassignments': [ShardReassignmentRecord],
@ -902,9 +902,9 @@ def get_block_root(state: BeaconState,
"""
Returns the block root at a recent ``slot``.
"""
earliest_slot_in_array = state.slot - len(state.latest_block_roots)
assert earliest_slot_in_array <= slot < state.slot
return state.latest_block_roots[slot - earliest_slot_in_array]
assert state.slot <= slot + LATEST_BLOCK_ROOTS_LENGTH
assert slot < state.slot
return state.latest_block_roots[slot % LATEST_BLOCK_ROOTS_LENGTH]
```
`get_block_root(_, s)` should always return `hash_tree_root` of the block in the beacon chain at slot `s`, and `get_shard_committees_at_slot(_, s)` should not change unless the [validator](#dfn-validator) registry changes.
@ -1145,8 +1145,7 @@ def get_initial_beacon_state(initial_validator_deposits: List[Deposit],
validator_registry_delta_chain_tip=ZERO_HASH,
# Randomness and committees
randao_mix=ZERO_HASH,
next_seed=ZERO_HASH,
latest_randao_mixes=[ZERO_HASH for _ in range(LATEST_RANDAO_MIXES_LENGTH)],
shard_committees_at_slots=[],
persistent_committees=[],
persistent_committee_reassignments=[],
@ -1399,6 +1398,7 @@ Below are the processing steps that happen at every slot.
* Set `state.slot += 1`.
* Set `state.validator_registry[get_beacon_proposer_index(state, state.slot)].randao_layers += 1`.
* Set `state.latest_randao_mixes[state.slot % LATEST_RANDAO_MIXES_LENGTH] = state.latest_randao_mixes[(state.slot - 1) % LATEST_RANDAO_MIXES_LENGTH]`
### Block roots
@ -1425,7 +1425,7 @@ Below are the processing steps that happen at every `block`.
* Let `repeat_hash(x, n) = x if n == 0 else repeat_hash(hash(x), n-1)`.
* Let `proposer = state.validator_registry[get_beacon_proposer_index(state, state.slot)]`.
* Verify that `repeat_hash(block.randao_reveal, proposer.randao_layers) == proposer.randao_commitment`.
* Set `state.randao_mix = xor(state.randao_mix, block.randao_reveal)`.
* Set `state.latest_randao_mixes[state.slot % LATEST_RANDAO_MIXES_LENGTH] = xor(state.latest_randao_mixes[state.slot % LATEST_RANDAO_MIXES_LENGTH], block.randao_reveal)`
* Set `proposer.randao_commitment = block.randao_reveal`.
* Set `proposer.randao_layers = 0`.
@ -1754,15 +1754,14 @@ Also perform the following updates:
* Set `state.validator_registry_latest_change_slot = state.slot`.
* Set `state.shard_committees_at_slots[:EPOCH_LENGTH] = state.shard_committees_at_slots[EPOCH_LENGTH:]`.
* Set `state.shard_committees_at_slots[EPOCH_LENGTH:] = get_new_shuffling(state.next_seed, state.validator_registry, next_start_shard)` where `next_start_shard = (state.shard_committees_at_slots[-1][-1].shard + 1) % SHARD_COUNT`.
* Set `state.next_seed = state.randao_mix`.
* Set `state.shard_committees_at_slots[EPOCH_LENGTH:] = get_new_shuffling(state.latest_randao_mixes[(state.slot - EPOCH_LENGTH) % LATEST_RANDAO_MIXES_LENGTH], state.validator_registry, next_start_shard)` where `next_start_shard = (state.shard_committees_at_slots[-1][-1].shard + 1) % SHARD_COUNT`.
If a validator registry update does _not_ happen do the following:
* Set `state.shard_committees_at_slots[:EPOCH_LENGTH] = state.shard_committees_at_slots[EPOCH_LENGTH:]`.
* Let `slots_since_finality = state.slot - state.validator_registry_latest_change_slot`.
* Let `start_shard = state.shard_committees_at_slots[0][0].shard`.
* If `slots_since_finality * EPOCH_LENGTH <= MIN_VALIDATOR_REGISTRY_CHANGE_INTERVAL` or `slots_since_finality` is an exact power of 2, set `state.shard_committees_at_slots[EPOCH_LENGTH:] = get_new_shuffling(state.next_seed, state.validator_registry, start_shard)` and set `state.next_seed = state.randao_mix`. Note that `start_shard` is not changed from the last epoch.
* If `slots_since_finality * EPOCH_LENGTH <= MIN_VALIDATOR_REGISTRY_CHANGE_INTERVAL` or `slots_since_finality` is an exact power of 2, set `state.shard_committees_at_slots[EPOCH_LENGTH:] = get_new_shuffling(state.latest_randao_mixes[(state.slot - CYCLE_LENGTH) % LATEST_RANDAO_MIXES_LENGTH], state.validator_registry, start_shard)`. Note that `start_shard` is not changed from the last epoch.
### Proposer reshuffling
@ -1774,8 +1773,8 @@ num_validators_to_reshuffle = len(active_validator_indices) // SHARD_PERSISTENT_
for i in range(num_validators_to_reshuffle):
# Multiplying i to 2 to ensure we have different input to all the required hashes in the shuffling
# and none of the hashes used for entropy in this loop will be the same
validator_index = active_validator_indices[hash(state.randao_mix + bytes8(i * 2)) % len(active_validator_indices)]
new_shard = hash(state.randao_mix + bytes8(i * 2 + 1)) % SHARD_COUNT
validator_index = active_validator_indices[hash(state.latest_randao_mixes[state.slot % LATEST_RANDAO_MIXES_LENGTH] + bytes8(i * 2)) % len(active_validator_indices)]
new_shard = hash(state.latest_randao_mixes[state.slot % LATEST_RANDAO_MIXES_LENGTH] + bytes8(i * 2 + 1)) % SHARD_COUNT
shard_reassignment_record = ShardReassignmentRecord(
validator_index=validator_index,
shard=new_shard,