def build_aggregate(attestations):
# All attestations are from the same slot, committee index and vote for
# same source, target and beacon block.
if len(attestations) == 0:
return []
aggregation_bits = Bitlist[specs.MAX_VALIDATORS_PER_COMMITTEE](
*([0] * len(attestations[0].aggregation_bits)))
for attestation in attestations:
validator_index_in_committee = attestation.aggregation_bits.index(1)
aggregation_bits[validator_index_in_committee] = True
return specs.Attestation(aggregation_bits=aggregation_bits,
data=attestations[0].data)
def honest_attest(validator, known_items):
# Unpacking
validator_index = validator.validator_index
store = validator.store
committee_slot = validator.data.current_attest_slot
committee_index = validator.data.current_committee_index
committee = validator.data.current_committee
# What am I attesting for?
block_root = validator.get_head()
head_state = store.block_states[block_root].copy()
if head_state.slot < committee_slot:
specs.process_slots(head_state, committee_slot)
start_slot = specs.compute_start_slot_at_epoch(
specs.get_current_epoch(head_state))
epoch_boundary_block_root = block_root if start_slot == head_state.slot else specs.get_block_root_at_slot(
head_state, start_slot)
tgt_checkpoint = specs.Checkpoint(
epoch=specs.get_current_epoch(head_state),
root=epoch_boundary_block_root)
att_data = specs.AttestationData(
index=committee_index,
slot=committee_slot,
beacon_block_root=block_root,
source=head_state.current_justified_checkpoint,
target=tgt_checkpoint)
# Set aggregation bits to myself only
committee_size = len(committee)
index_in_committee = committee.index(validator_index)
aggregation_bits = Bitlist[specs.MAX_VALIDATORS_PER_COMMITTEE](
*([0] * committee_size))
aggregation_bits[
index_in_committee] = True # set the aggregation bit of the validator to True
attestation = specs.Attestation(aggregation_bits=aggregation_bits,
data=att_data)
# print(validator.validator_index, "attests for slot", committee_slot)
return attestation
def honest_attest(state, validator_index):
# Given state w-[s], validators in committees of slot `s-1` form their attestations
# In several places here, we need to check whether `s` is the first slot of a new epoch.
current_epoch = specs.get_current_epoch(state)
previous_epoch = specs.get_previous_epoch(state)
# Since everyone is honest, we can assume that validators attesting during some epoch e
# choose the first block of e as their target, and the first block of e-1 as their source
# checkpoint.
#
# So let's assume the validator here is making an attestation at slot s in epoch e:
#
# - If the `state` variable is at epoch e, then the first block of epoch e-1 is
# a checkpoint held in `state.current_justified_checkpoint`.
# The target checkpoint root is obtained by calling
# `get_block_root(state, current_epoch)` (since current_epoch = e).
#
# - If the `state` variable is at epoch e+1, then the first block of epoch e-1
# is a checkpoint held in `state.previous_justified_checkpoint`,
# since in the meantime the first block of e was justified.
# This is the case when s is the last slot of epoch e.
# The target checkpoint root is obtained by calling
# `get_block_root(state, previous_epoch)` (since current_epoch = e+1).
#
# ... still here?
# If `state` is already at the start of a new epoch e+1
if state.slot == specs.compute_start_slot_at_epoch(current_epoch):
# `committee_slot` is equal to s-1
(committee, committee_index,
committee_slot) = specs.get_committee_assignment(
state, previous_epoch, validator_index)
# Since we are at state w-[s], we can get the block root of the block at slot s-1.
block_root = specs.get_block_root_at_slot(state, committee_slot)
src_checkpoint = specs.Checkpoint(
epoch=state.previous_justified_checkpoint.epoch,
root=state.previous_justified_checkpoint.root)
tgt_checkpoint = specs.Checkpoint(epoch=previous_epoch,
root=specs.get_block_root(
state, previous_epoch))
# Otherwise, if `state` is at epoch e
else:
# `committee_slot` is equal to s-1
(committee, committee_index,
committee_slot) = specs.get_committee_assignment(
state, current_epoch, validator_index)
# Since we are at state w-[s], we can get the block root of the block at slot s-1.
block_root = specs.get_block_root_at_slot(state, committee_slot)
src_checkpoint = specs.Checkpoint(
epoch=state.current_justified_checkpoint.epoch,
root=state.current_justified_checkpoint.root)
tgt_checkpoint = specs.Checkpoint(epoch=current_epoch,
root=specs.get_block_root(
state, current_epoch))
att_data = specs.AttestationData(index=committee_index,
slot=committee_slot,
beacon_block_root=block_root,
source=src_checkpoint,
target=tgt_checkpoint)
# if log: print("attestation for source", src_checkpoint.epoch, "and target", tgt_checkpoint.epoch)
# For now we disregard aggregation of attestations.
# Some validators are chosen as aggregators: they take a bunch of identical attestations
# and join them together in one object,
# with `aggregation_bits` identifying which validators are part of the aggregation.
committee_size = len(committee)
index_in_committee = committee.index(validator_index)
aggregation_bits = Bitlist[specs.MAX_VALIDATORS_PER_COMMITTEE](
*([0] * committee_size))
aggregation_bits[
index_in_committee] = True # set the aggregation bits of the validator to True
attestation = specs.Attestation(aggregation_bits=aggregation_bits,
data=att_data)
return attestation