nimbus-eth2/beacon_chain/spec/validator.nim

238 lines
10 KiB
Nim

# Copyright (c) 2018-2019 Status Research & Development GmbH
# Licensed and distributed under either of
# * MIT license (license terms in the root directory or at http://opensource.org/licenses/MIT).
# * Apache v2 license (license terms in the root directory or at http://www.apache.org/licenses/LICENSE-2.0).
# at your option. This file may not be copied, modified, or distributed except according to those terms.
# Helpers and functions pertaining to managing the validator set
import
options, nimcrypto, sequtils, math,
eth/common,
../ssz,
./crypto, ./datatypes, ./digest, ./helpers
# https://github.com/ethereum/eth2.0-specs/blob/v0.3.0/specs/core/0_beacon-chain.md#get_shuffling
# https://github.com/ethereum/eth2.0-specs/blob/v0.3.0/specs/core/0_beacon-chain.md#get_permuted_index
func get_shuffled_seq*(seed: Eth2Digest,
list_size: uint64,
): seq[ValidatorIndex] =
## Via https://github.com/protolambda/eth2-shuffle/blob/master/shuffle.go
## Shuffles ``validators`` into crosslink committees seeded by ``seed`` and
## ``slot``.
## Returns a list of ``SLOTS_PER_EPOCH * committees_per_slot`` committees
## where each committee is itself a list of validator indices.
##
## Invert the inner/outer loops from the spec, essentially. Most useful
## hash result re-use occurs within a round.
var
# Share these buffers.
pivot_buffer: array[(32+1), byte]
source_buffer: array[(32+1+4), byte]
shuffled_active_validator_indices = mapIt(
0 ..< list_size.int, it.ValidatorIndex)
sources = repeat(Eth2Digest(), (list_size div 256) + 1)
## The pivot's a function of seed and round only.
## This doesn't change across rounds.
pivot_buffer[0..31] = seed.data
source_buffer[0..31] = seed.data
for round in 0 ..< SHUFFLE_ROUND_COUNT:
let round_bytes1 = int_to_bytes1(round)[0]
pivot_buffer[32] = round_bytes1
source_buffer[32] = round_bytes1
# Only one pivot per round.
let pivot = bytes_to_int(eth2hash(pivot_buffer).data[0..7]) mod list_size
## Only need to run, per round, position div 256 hashes, so precalculate
## them. This consumes memory, but for low-memory devices, it's possible
## to mitigate by some light LRU caching and similar.
for reduced_position in 0 ..< sources.len:
source_buffer[33..36] = int_to_bytes4(reduced_position.uint64)
sources[reduced_position] = eth2hash(source_buffer)
## Iterate over all the indices. This was in get_permuted_index, but large
## efficiency gains exist in caching and re-using data.
for index in 0 ..< list_size.int:
let
cur_idx_permuted = shuffled_active_validator_indices[index]
flip = ((list_size + pivot) - cur_idx_permuted.uint64) mod list_size
position = max(cur_idx_permuted, flip.int)
let
source = sources[position div 256].data
byte_value = source[(position mod 256) div 8]
bit = (byte_value shr (position mod 8)) mod 2
if bit != 0:
shuffled_active_validator_indices[index] = flip.ValidatorIndex
result = shuffled_active_validator_indices
# https://github.com/ethereum/eth2.0-specs/blob/v0.3.0/specs/core/0_beacon-chain.md#get_shuffling
func get_shuffling*(seed: Eth2Digest,
validators: openArray[Validator],
epoch: Epoch,
shuffling_cache: ShufflingCache
): seq[seq[ValidatorIndex]] =
## This function is factored to facilitate testing with
## https://github.com/ethereum/eth2.0-test-generators/tree/master/permutated_index
## test vectors, which the split of get_shuffling obfuscates.
let list_size = validators.len.uint64
let
active_validator_indices = get_active_validator_indices(validators, epoch)
committees_per_epoch = get_epoch_committee_count(
len(active_validator_indices)).int
# Both mapIt-type-conversions are an SSZ artifact. TODO remove.
shuffled_seq =
if shuffling_cache.seeds[0] == seed and
shuffling_cache.list_sizes[0] == list_size:
mapIt(shuffling_cache.shuffling_0, it.ValidatorIndex)
elif shuffling_cache.seeds[1] == seed and
shuffling_cache.list_sizes[1] == list_size:
mapIt(shuffling_cache.shuffling_1, it.ValidatorIndex)
else:
get_shuffled_seq(seed, list_size)
# Split the shuffled list into committees_per_epoch pieces
result = split(shuffled_seq, committees_per_epoch)
assert result.len() == committees_per_epoch # what split should do..
# https://github.com/ethereum/eth2.0-specs/blob/v0.3.0/specs/core/0_beacon-chain.md#get_previous_epoch_committee_count
func get_previous_epoch_committee_count(state: BeaconState): uint64 =
# Return the number of committees in the previous epoch of the given ``state``.
let previous_active_validators = get_active_validator_indices(
state.validator_registry,
state.previous_shuffling_epoch,
)
get_epoch_committee_count(len(previous_active_validators))
# https://github.com/ethereum/eth2.0-specs/blob/v0.3.0/specs/core/0_beacon-chain.md#get_next_epoch_committee_count
func get_next_epoch_committee_count(state: BeaconState): uint64 =
## Return the number of committees in the next epoch of the given ``state``.
let next_active_validators = get_active_validator_indices(
state.validator_registry,
get_current_epoch(state) + 1,
)
get_epoch_committee_count(len(next_active_validators))
# https://github.com/ethereum/eth2.0-specs/blob/v0.3.0/specs/core/0_beacon-chain.md#get_previous_epoch
func get_previous_epoch(state: BeaconState): Epoch =
## Return the previous epoch of the given ``state``.
## If the current epoch is ``GENESIS_EPOCH``, return ``GENESIS_EPOCH``.
let current_epoch = get_current_epoch(state)
if current_epoch == GENESIS_EPOCH:
GENESIS_EPOCH
else:
current_epoch - 1
# https://github.com/ethereum/eth2.0-specs/blob/v0.3.0/specs/core/0_beacon-chain.md#get_crosslink_committees_at_slot
func get_crosslink_committees_at_slot*(state: BeaconState, slot: Slot,
registry_change: bool = false):
seq[CrosslinkCommittee] =
## Returns the list of ``(committee, shard)`` tuples for the ``slot``.
##
## Note: There are two possible shufflings for crosslink committees for a
## ``slot`` in the next epoch -- with and without a `registry_change`
let
epoch = slot_to_epoch(slot)
current_epoch = get_current_epoch(state)
previous_epoch = get_previous_epoch(state)
next_epoch = current_epoch + 1
assert previous_epoch <= epoch,
"Previous epoch: " & $humaneEpochNum(previous_epoch) &
", epoch: " & $humaneEpochNum(epoch) &
", Next epoch: " & $humaneEpochNum(next_epoch)
assert epoch <= next_epoch,
"Previous epoch: " & $humaneEpochNum(previous_epoch) &
", epoch: " & $humaneEpochNum(epoch) &
", Next epoch: " & $humaneEpochNum(next_epoch)
# TODO - Hack: used to be "epoch < next_epoch" (exlusive interval)
# until https://github.com/status-im/nim-beacon-chain/issues/97
template get_epoch_specific_params(): auto =
if epoch < current_epoch:
let
## TODO this might be pointless copying; RVO exists, but not sure if
## Nim optimizes out both copies per. Could directly construct tuple
## but this hews closer to spec helper code.
committees_per_epoch = get_previous_epoch_committee_count(state)
seed = state.previous_shuffling_seed
shuffling_epoch = state.previous_shuffling_epoch
shuffling_start_shard = state.previous_shuffling_start_shard
(committees_per_epoch, seed, shuffling_epoch, shuffling_start_shard)
elif epoch == current_epoch:
let
committees_per_epoch = get_current_epoch_committee_count(state)
seed = state.current_shuffling_seed
shuffling_epoch = state.current_shuffling_epoch
shuffling_start_shard = state.current_shuffling_start_shard
(committees_per_epoch, seed, shuffling_epoch, shuffling_start_shard)
else:
assert epoch == next_epoch
let
current_committees_per_epoch = get_current_epoch_committee_count(state)
committees_per_epoch = get_next_epoch_committee_count(state)
shuffling_epoch = next_epoch
epochs_since_last_registry_update = current_epoch - state.validator_registry_update_epoch
condition = epochs_since_last_registry_update > 1'u64 and
is_power_of_2(epochs_since_last_registry_update)
seed = if registry_change or condition:
generate_seed(state, next_epoch)
else:
state.current_shuffling_seed
shuffling_start_shard =
if registry_change:
(state.current_shuffling_start_shard +
current_committees_per_epoch) mod SHARD_COUNT
else:
state.current_shuffling_start_shard
(committees_per_epoch, seed, shuffling_epoch, shuffling_start_shard)
let (committees_per_epoch, seed, shuffling_epoch, shuffling_start_shard) =
get_epoch_specific_params()
let
shuffling = get_shuffling(
seed,
state.validator_registry,
shuffling_epoch,
state.shuffling_cache
)
offset = slot mod SLOTS_PER_EPOCH
committees_per_slot = committees_per_epoch div SLOTS_PER_EPOCH
slot_start_shard = (shuffling_start_shard + committees_per_slot * offset) mod SHARD_COUNT
for i in 0 ..< committees_per_slot.int:
result.add (
shuffling[(committees_per_slot * offset + i.uint64).int],
(slot_start_shard + i.uint64) mod SHARD_COUNT
)
# https://github.com/ethereum/eth2.0-specs/blob/v0.3.0/specs/core/0_beacon-chain.md#get_beacon_proposer_index
func get_beacon_proposer_index*(state: BeaconState, slot: Slot): ValidatorIndex =
## From Casper RPJ mini-spec:
## When slot i begins, validator Vidx is expected
## to create ("propose") a block, which contains a pointer to some parent block
## that they perceive as the "head of the chain",
## and includes all of the **attestations** that they know about
## that have not yet been included into that chain.
##
## idx in Vidx == p(i mod N), pi being a random permutation of validators indices (i.e. a committee)
## Returns the beacon proposer index for the ``slot``.
# TODO this index is invalid outside of the block state transition function
# because presently, `state.slot += 1` happens before this function
# is called - see also testutil.getNextBeaconProposerIndex
# TODO is the above still true? the shuffling has changed since it was written
let (first_committee, _) = get_crosslink_committees_at_slot(state, slot)[0]
let idx = int(slot mod uint64(first_committee.len))
first_committee[idx]