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Separated block roots and randao mixes length, and fixed per-slot randao updates

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vbuterin 2018-12-17 14:04:04 -05:00 committed by GitHub
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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) | block roots |
| `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`.
@ -1153,7 +1154,7 @@ def get_initial_beacon_state(initial_validator_deposits: List[Deposit],
validator_registry_delta_chain_tip=ZERO_HASH,
# Randomness and committees
latest_randao_mixes=[ZERO_HASH for _ in range(LATEST_BLOCK_ROOTS_LENGTH)],
latest_randao_mixes=[ZERO_HASH for _ in range(LATEST_RANDAO_MIXES_LENGTH)],
shard_committees_at_slots=[],
persistent_committees=[],
persistent_committee_reassignments=[],
@ -1387,11 +1388,12 @@ 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.latest_randao_mixes[(block.slot - 1) % LATEST_RANDAO_MIXES_LENGTH]`
### Block roots
* Let `previous_block_root` be the `hash_tree_root` of the previous beacon block processed in the chain.
* Set `state.latest_block_roots = state.latest_block_roots[1:] + [previous_block_root]`.
* Set `state.latest_block_roots[(block.slot - 1) % LATEST_BLOCK_ROOTS_LENGTH] = previous_block_root`.
* If `state.slot % LATEST_BLOCK_ROOTS_LENGTH == 0` append `merkle_root(state.latest_block_roots)` to `state.batched_block_roots`.
## Per-block processing
@ -1413,7 +1415,7 @@ 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.latest_randao_mixes[block.slot % LATEST_BLOCK_ROOTS_LENGTH] = xor(state.latest_randao_mixes[(block.slot - 1) % LATEST_BLOCK_ROOTS_LENGTH], block.randao_reveal)`
* Set `state.latest_randao_mixes[block.slot % LATEST_RANDAO_MIXES_LENGTH] = xor(state.latest_randao_mixes[block.slot % LATEST_RANDAO_MIXES_LENGTH], block.randao_reveal)`
* Set `proposer.randao_commitment = block.randao_reveal`.
* Set `proposer.randao_layers = 0`.
@ -1747,14 +1749,14 @@ 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.latest_randao_mixes[(state.slot - CYCLE_LENGTH) % LATEST_BLOCK_ROOTS_LENGTH], state.validator_registry, next_start_shard)` where `next_start_shard = (state.shard_committees_at_slots[-1][-1].shard + 1) % SHARD_COUNT`.
* 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.latest_randao_mixes[(state.slot - CYCLE_LENGTH) % LATEST_BLOCK_ROOTS_LENGTH], state.validator_registry, start_shard)`. 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
@ -1766,8 +1768,8 @@ 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.latest_randao_mixes[state.slot % LATEST_BLOCK_ROOTS_LENGTH] + bytes8(i * 2)) % len(active_validator_indices)]
new_shard = hash(state.latest_randao_mixes[state.slot % LATEST_BLOCK_ROOTS_LENGTH] + 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,