From 429e5721f224c5ac61e55aa9eb277f34bef7700d Mon Sep 17 00:00:00 2001 From: Justin Date: Wed, 2 Jan 2019 14:20:01 +0000 Subject: [PATCH] RANDAO hash chain and no stale shuffles * Make RANDAO into a hash chain (this makes it easy for applications to prove the intermediate RANDAO reveals). * Include `state.slot` when shuffle to avoid stale shuffles with skip slots --- specs/core/0_beacon-chain.md | 14 ++++++++------ 1 file changed, 8 insertions(+), 6 deletions(-) diff --git a/specs/core/0_beacon-chain.md b/specs/core/0_beacon-chain.md index beafa9372..97f4ea97c 100644 --- a/specs/core/0_beacon-chain.md +++ b/specs/core/0_beacon-chain.md @@ -187,6 +187,7 @@ Unless otherwise indicated, code appearing in `this style` is to be interpreted | - | - | | `INITIAL_FORK_VERSION` | `0` | | `INITIAL_SLOT_NUMBER` | `0` | +| `GENESIS_START_SHARD` | `0` | | `ZERO_HASH` | `bytes([0] * 32)` | ### Time parameters @@ -863,10 +864,11 @@ def split(values: List[Any], split_count: int) -> List[Any]: ```python def get_new_shuffling(seed: Hash32, + slot: int, validators: List[ValidatorRecord], crosslinking_start_shard: int) -> List[List[ShardCommittee]]: """ - Shuffles ``validators`` into shard committees using ``seed`` as entropy. + Shuffles ``validators`` into shard committees using ``seed`` and ``slot`` as entropy. """ active_validator_indices = get_active_validator_indices(validators) @@ -879,7 +881,7 @@ def get_new_shuffling(seed: Hash32, ) # Shuffle with seed - shuffled_active_validator_indices = shuffle(active_validator_indices, seed) + shuffled_active_validator_indices = shuffle(active_validator_indices, xor(seed, Hash32(slot)) # Split the shuffled list into epoch_length pieces validators_per_slot = split(shuffled_active_validator_indices, EPOCH_LENGTH) @@ -1221,7 +1223,7 @@ def get_initial_beacon_state(initial_validator_deposits: List[Deposit], update_validator_status(state, validator_index, ACTIVE) # set initial committee shuffling - initial_shuffling = get_new_shuffling(ZERO_HASH, state.validator_registry, 0) + initial_shuffling = get_new_shuffling(ZERO_HASH, state.slot, state.validator_registry, GENESIS_START_SHARD) state.shard_committees_at_slots = initial_shuffling + initial_shuffling return state @@ -1458,7 +1460,7 @@ 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[state.slot % LATEST_RANDAO_MIXES_LENGTH] = xor(state.latest_randao_mixes[state.slot % LATEST_RANDAO_MIXES_LENGTH], block.randao_reveal)` +* Set `state.latest_randao_mixes[state.slot % LATEST_RANDAO_MIXES_LENGTH] = hash(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`. @@ -1783,14 +1785,14 @@ 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 - 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`. +* Set `state.shard_committees_at_slots[EPOCH_LENGTH:] = get_new_shuffling(state.latest_randao_mixes[(state.slot - EPOCH_LENGTH) % LATEST_RANDAO_MIXES_LENGTH], state.slot, 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 `epochs_since_last_registry_change = (state.slot - state.validator_registry_latest_change_slot) // EPOCH_LENGTH`. * Let `start_shard = state.shard_committees_at_slots[0][0].shard`. -* If `epochs_since_last_registry_change` is an exact power of 2, 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, start_shard)`. Note that `start_shard` is not changed from the last epoch. +* If `epochs_since_last_registry_change` is an exact power of 2, set `state.shard_committees_at_slots[EPOCH_LENGTH:] = get_new_shuffling(state.latest_randao_mixes[(state.slot - EPOCH_LENGTH) % LATEST_RANDAO_MIXES_LENGTH], state.slot, state.validator_registry, start_shard)`. Note that `start_shard` is not changed from the last epoch. ### Final updates