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nimbus-eth2/beacon_chain/spec/validator.nim

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# Copyright (c) 2018-2022 Status Research & Development GmbH
# Licensed and distributed under either of
# * MIT license (license terms in the root directory or at https://opensource.org/licenses/MIT).
# * Apache v2 license (license terms in the root directory or at https://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
when (NimMajor, NimMinor) < (1, 4):
{.push raises: [Defect].}
else:
{.push raises: [].}
import
std/[options, math, tables],
./datatypes/[phase0, altair, bellatrix],
./helpers
export helpers
const
SEED_SIZE = sizeof(Eth2Digest)
ROUND_SIZE = 1
POSITION_WINDOW_SIZE = 4
PIVOT_VIEW_SIZE = SEED_SIZE + ROUND_SIZE
TOTAL_SIZE = PIVOT_VIEW_SIZE + POSITION_WINDOW_SIZE
# https://github.com/ethereum/consensus-specs/blob/v1.3.0-alpha.0/specs/phase0/beacon-chain.md#compute_shuffled_index
# https://github.com/ethereum/consensus-specs/blob/v1.3.0-alpha.0/specs/phase0/beacon-chain.md#compute_committee
# Port of https://github.com/protolambda/zrnt/blob/master/eth2/beacon/shuffle.go
# Shuffles or unshuffles, depending on the `dir` (true for shuffling, false for unshuffling
func shuffle_list*(input: var seq[ValidatorIndex], seed: Eth2Digest) =
let list_size = input.lenu64
if list_size <= 1: return
var buf {.noinit.}: array[TOTAL_SIZE, byte]
# Seed is always the first 32 bytes of the hash input, we never have to change
# this part of the buffer.
buf[0..<32] = seed.data
# The original code includes a direction flag, but only the reverse direction
# is used in eth2, so we simplify it here
for r in 0'u8..<SHUFFLE_ROUND_COUNT.uint8:
# spec: pivot = bytes_to_int(hash(seed + int_to_bytes1(round))[0:8]) % list_size
# This is the "int_to_bytes1(round)", appended to the seed.
buf[SEED_SIZE] = (SHUFFLE_ROUND_COUNT.uint8 - r - 1)
# Seed is already in place, now just hash the correct part of the buffer,
# and take a uint64 from it, and modulo it to get a pivot within range.
let
pivotDigest = eth2digest(buf.toOpenArray(0, PIVOT_VIEW_SIZE - 1))
pivot = bytes_to_uint64(pivotDigest.data.toOpenArray(0, 7)) mod list_size
# Split up the for-loop in two:
# 1. Handle the part from 0 (incl) to pivot (incl). This is mirrored around
# (pivot / 2)
# 2. Handle the part from pivot (excl) to N (excl). This is mirrored around
# ((pivot / 2) + (size/2))
# The pivot defines a split in the array, with each of the splits mirroring
# their data within the split.
# Print out some example even/odd sized index lists, with some even/odd pivots,
# and you can deduce how the mirroring works exactly.
# Note that the mirror is strict enough to not consider swapping the index
# @mirror with itself.
# Since we are iterating through the "positions" in order, we can just
# repeat the hash every 256th position.
# No need to pre-compute every possible hash for efficiency like in the
# example code.
# We only need it consecutively (we are going through each in reverse order
# however, but same thing)
# spec: source = hash(seed + int_to_bytes1(round) + int_to_bytes4(position // 256))
# - seed is still in 0:32 (excl., 32 bytes)
# - round number is still in 32
# - mix in the position for randomness, except the last byte of it,
# which will be used later to select a bit from the resulting hash.
# We start from the pivot position, and work back to the mirror position
# (of the part left to the pivot).
# This makes us process each pear exactly once (instead of unnecessarily
# twice, like in the spec)
buf[33..<37] = uint_to_bytes(uint32(pivot shr 8))
var
mirror = (pivot + 1) shr 1
source = eth2digest(buf)
byteV = source.data[(pivot and 0xff) shr 3]
i = 0'u64
j = pivot
template shuffle =
while i < mirror:
# The pair is i,j. With j being the bigger of the two, hence the "position" identifier of the pair.
# Every 256th bit (aligned to j).
if (j and 0xff) == 0xff:
# just overwrite the last part of the buffer, reuse the start (seed, round)
buf[33..<37] = uint_to_bytes(uint32(j shr 8))
source = eth2digest(buf)
# Same trick with byte retrieval. Only every 8th.
if (j and 0x07) == 0x7:
byteV = source.data[(j and 0xff'u64) shr 3]
let
bitV = (byteV shr (j and 0x7)) and 0x1
if bitV == 1:
swap(input[i], input[j])
i.inc
j.dec
shuffle
# Now repeat, but for the part after the pivot.
mirror = (pivot + list_size + 1) shr 1
let lend = list_size - 1
# Again, seed and round input is in place, just update the position.
# We start at the end, and work back to the mirror point.
# This makes us process each pear exactly once (instead of unnecessarily twice, like in the spec)
buf[33..<37] = uint_to_bytes(uint32(lend shr 8))
source = eth2digest(buf)
byteV = source.data[(lend and 0xff) shr 3]
i = pivot + 1'u64
j = lend
shuffle
func get_shuffled_active_validator_indices*(
state: ForkyBeaconState, epoch: Epoch): seq[ValidatorIndex] =
# Non-spec function, to cache a data structure from which one can cheaply
# compute both get_active_validator_indexes() and get_beacon_committee().
var active_validator_indices = get_active_validator_indices(state, epoch)
shuffle_list(
active_validator_indices, get_seed(state, epoch, DOMAIN_BEACON_ATTESTER))
active_validator_indices
func get_shuffled_active_validator_indices*(
cache: var StateCache, state: ForkyBeaconState, epoch: Epoch):
var seq[ValidatorIndex] =
# `cache` comes first because of nim's borrowing rules for the `var` return -
# the `var` returns avoids copying the validator set.
cache.shuffled_active_validator_indices.withValue(epoch, validator_indices) do:
return validator_indices[]
do:
let indices = get_shuffled_active_validator_indices(state, epoch)
return cache.shuffled_active_validator_indices.mgetOrPut(epoch, indices)
func get_shuffled_active_validator_indices*(
cache: var StateCache, state: ForkedHashedBeaconState, epoch: Epoch):
seq[ValidatorIndex] =
withState(state):
cache.get_shuffled_active_validator_indices(forkyState.data, epoch)
# https://github.com/ethereum/consensus-specs/blob/v1.3.0-alpha.0/specs/phase0/beacon-chain.md#get_active_validator_indices
func count_active_validators*(state: ForkyBeaconState,
epoch: Epoch,
cache: var StateCache): uint64 =
cache.get_shuffled_active_validator_indices(state, epoch).lenu64
# https://github.com/ethereum/consensus-specs/blob/v1.3.0-alpha.0/specs/phase0/beacon-chain.md#get_committee_count_per_slot
func get_committee_count_per_slot*(num_active_validators: uint64): uint64 =
clamp(
num_active_validators div SLOTS_PER_EPOCH div TARGET_COMMITTEE_SIZE,
1'u64, MAX_COMMITTEES_PER_SLOT)
func get_committee_count_per_slot*(state: ForkyBeaconState,
epoch: Epoch,
cache: var StateCache): uint64 =
## Return the number of committees at ``slot``.
let
active_validator_count = count_active_validators(state, epoch, cache)
get_committee_count_per_slot(active_validator_count)
func get_committee_count_per_slot*(state: ForkedHashedBeaconState,
epoch: Epoch,
cache: var StateCache): uint64 =
withState(state):
get_committee_count_per_slot(forkyState.data, epoch, cache)
iterator get_committee_indices*(committee_count_per_slot: uint64): CommitteeIndex =
for idx in 0'u64..<min(committee_count_per_slot, MAX_COMMITTEES_PER_SLOT):
let committee_index = CommitteeIndex.init(idx).expect("value clamped")
yield committee_index
# https://github.com/ethereum/consensus-specs/blob/v1.3.0-alpha.0/specs/phase0/beacon-chain.md#compute_committee
func compute_committee_slice*(
active_validators, index, count: uint64): Slice[int] =
doAssert active_validators <= ValidatorIndex.high.uint64
if index < count:
let
start = (active_validators * index) div count
endIdx = (active_validators * (index + 1)) div count
start.int..(endIdx.int - 1)
else:
0 .. -1
iterator compute_committee*(shuffled_indices: seq[ValidatorIndex],
index: uint64, count: uint64): (int, ValidatorIndex) =
let
slice = compute_committee_slice(shuffled_indices.lenu64, index, count)
var idx = 0
for i in slice:
yield (idx, shuffled_indices[i])
idx += 1
func compute_committee*(shuffled_indices: seq[ValidatorIndex],
index: uint64, count: uint64): seq[ValidatorIndex] =
## Return the committee corresponding to ``indices``, ``seed``, ``index``,
## and committee ``count``.
## In this version, we pass in the shuffled indices meaning we no longer need
## the seed.
let
slice = compute_committee_slice(shuffled_indices.lenu64, index, count)
# In spec, this calls get_shuffled_index() every time, but that's wasteful
# Here, get_beacon_committee() gets the shuffled version.
shuffled_indices[slice]
func compute_committee_len*(
active_validators, index, count: uint64): uint64 =
## Return the committee corresponding to ``indices``, ``seed``, ``index``,
## and committee ``count``.
let
slice = compute_committee_slice(active_validators, index, count)
(slice.b - slice.a + 1).uint64
# https://github.com/ethereum/consensus-specs/blob/v1.3.0-alpha.0/specs/phase0/beacon-chain.md#get_beacon_committee
iterator get_beacon_committee*(
state: ForkyBeaconState, slot: Slot, index: CommitteeIndex,
cache: var StateCache): (int, ValidatorIndex) =
## Return the beacon committee at ``slot`` for ``index``.
let
epoch = epoch(slot)
committees_per_slot = get_committee_count_per_slot(state, epoch, cache)
for index_in_committee, idx in compute_committee(
cache.get_shuffled_active_validator_indices(state, epoch),
(slot mod SLOTS_PER_EPOCH) * committees_per_slot +
index.uint64,
committees_per_slot * SLOTS_PER_EPOCH
): yield (index_in_committee, idx)
func get_beacon_committee*(
state: ForkyBeaconState, slot: Slot, index: CommitteeIndex,
cache: var StateCache): seq[ValidatorIndex] =
## Return the beacon committee at ``slot`` for ``index``.
let
epoch = epoch(slot)
committees_per_slot = get_committee_count_per_slot(state, epoch, cache)
compute_committee(
cache.get_shuffled_active_validator_indices(state, epoch),
(slot mod SLOTS_PER_EPOCH) * committees_per_slot +
index.uint64,
committees_per_slot * SLOTS_PER_EPOCH
)
func get_beacon_committee*(
state: ForkedHashedBeaconState, slot: Slot, index: CommitteeIndex,
cache: var StateCache): seq[ValidatorIndex] =
# This one is used by tests/, ncli/, and a couple of places in RPC
# TODO use the iterator version alone, to remove the risk of using
# diverging get_beacon_committee() in tests and beacon_chain/ by a
# wrapper approach (e.g., toSeq). This is a perf tradeoff for test
# correctness/consistency.
withState(state):
get_beacon_committee(forkyState.data, slot, index, cache)
# https://github.com/ethereum/consensus-specs/blob/v1.3.0-alpha.0/specs/phase0/beacon-chain.md#get_beacon_committee
func get_beacon_committee_len*(
state: ForkyBeaconState, slot: Slot, index: CommitteeIndex,
cache: var StateCache): uint64 =
# Return the number of members in the beacon committee at ``slot`` for ``index``.
let
epoch = epoch(slot)
committees_per_slot = get_committee_count_per_slot(state, epoch, cache)
compute_committee_len(
count_active_validators(state, epoch, cache),
(slot mod SLOTS_PER_EPOCH) * committees_per_slot +
index.uint64,
committees_per_slot * SLOTS_PER_EPOCH
)
func get_beacon_committee_len*(
state: ForkedHashedBeaconState, slot: Slot, index: CommitteeIndex,
cache: var StateCache): uint64 =
# This one is used by tests
withState(state):
get_beacon_committee_len(forkyState.data, slot, index, cache)
# https://github.com/ethereum/consensus-specs/blob/v1.3.0-alpha.0/specs/phase0/beacon-chain.md#compute_shuffled_index
func compute_shuffled_index*(
index: uint64, index_count: uint64, seed: Eth2Digest): uint64 =
## Return the shuffled index corresponding to ``seed`` (and ``index_count``).
doAssert index < index_count
var
source_buffer {.noinit.}: array[(32+1+4), byte]
cur_idx_permuted = index
source_buffer[0..31] = seed.data
# Swap or not (https://link.springer.com/content/pdf/10.1007%2F978-3-642-32009-5_1.pdf)
# See the 'generalized domain' algorithm on page 3
for current_round in 0'u8 ..< SHUFFLE_ROUND_COUNT.uint8:
source_buffer[32] = current_round
let
# If using multiple indices, can amortize this
pivot =
bytes_to_uint64(eth2digest(source_buffer.toOpenArray(0, 32)).data.toOpenArray(0, 7)) mod
index_count
flip = ((index_count + pivot) - cur_idx_permuted) mod index_count
position = max(cur_idx_permuted, flip)
source_buffer[33..36] = uint_to_bytes(uint32(position shr 8))
let
source = eth2digest(source_buffer).data
byte_value = source[(position mod 256) shr 3]
bit = (byte_value shr (position mod 8)) mod 2
cur_idx_permuted = if bit != 0: flip else: cur_idx_permuted
cur_idx_permuted
# https://github.com/ethereum/consensus-specs/blob/v1.3.0-alpha.0/specs/phase0/beacon-chain.md#compute_proposer_index
func compute_proposer_index(state: ForkyBeaconState,
indices: seq[ValidatorIndex], seed: Eth2Digest): Option[ValidatorIndex] =
## Return from ``indices`` a random index sampled by effective balance.
const MAX_RANDOM_BYTE = 255
if len(indices) == 0:
return none(ValidatorIndex)
let seq_len = indices.lenu64
var
i = 0'u64
buffer: array[32+8, byte]
buffer[0..31] = seed.data
while true:
buffer[32..39] = uint_to_bytes(i div 32)
let
candidate_index =
indices[compute_shuffled_index(i mod seq_len, seq_len, seed)]
random_byte = (eth2digest(buffer).data)[i mod 32]
effective_balance = state.validators[candidate_index].effective_balance
if effective_balance * MAX_RANDOM_BYTE >=
MAX_EFFECTIVE_BALANCE * random_byte:
return some(candidate_index)
i += 1
# https://github.com/ethereum/consensus-specs/blob/v1.3.0-alpha.0/specs/phase0/beacon-chain.md#get_beacon_proposer_index
func get_beacon_proposer_index*(
state: ForkyBeaconState, cache: var StateCache, slot: Slot):
Option[ValidatorIndex] =
let epoch = get_current_epoch(state)
if slot.epoch() != epoch:
# compute_proposer_index depends on `effective_balance`, therefore the
# beacon proposer index can only be computed for the "current" epoch:
# https://github.com/ethereum/consensus-specs/pull/772#issuecomment-475574357
return none(ValidatorIndex)
cache.beacon_proposer_indices.withValue(slot, proposer) do:
return proposer[]
do:
# Return the beacon proposer index at the current slot.
var buffer: array[32 + 8, byte]
buffer[0..31] = get_seed(state, epoch, DOMAIN_BEACON_PROPOSER).data
# There's exactly one beacon proposer per slot - the same validator may
# however propose several times in the same epoch (however unlikely)
let
# active validator indices are kept in cache but sorting them takes
# quite a while
indices = get_active_validator_indices(state, epoch)
var res: Option[ValidatorIndex]
for epoch_slot in epoch.slots():
buffer[32..39] = uint_to_bytes(epoch_slot.asUInt64)
let seed = eth2digest(buffer)
let pi = compute_proposer_index(state, indices, seed)
if epoch_slot == slot:
res = pi
cache.beacon_proposer_indices[epoch_slot] = pi
return res
# https://github.com/ethereum/consensus-specs/blob/v1.3.0-alpha.0/specs/phase0/beacon-chain.md#get_beacon_proposer_index
func get_beacon_proposer_index*(state: ForkyBeaconState, cache: var StateCache):
Option[ValidatorIndex] =
get_beacon_proposer_index(state, cache, state.slot)
func get_beacon_proposer_index*(state: ForkedHashedBeaconState,
cache: var StateCache, slot: Slot):
Option[ValidatorIndex] =
withState(state):
get_beacon_proposer_index(forkyState.data, cache, slot)
# https://github.com/ethereum/consensus-specs/blob/v1.3.0-alpha.0/specs/phase0/validator.md#aggregation-selection
func is_aggregator*(committee_len: uint64, slot_signature: ValidatorSig): bool =
let
modulo = max(1'u64, committee_len div TARGET_AGGREGATORS_PER_COMMITTEE)
bytes_to_uint64(eth2digest(
slot_signature.toRaw()).data.toOpenArray(0, 7)) mod modulo == 0
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