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add previous_crosslink_root and enforce crosslinks form a chain

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Danny Ryan 2019-04-07 17:55:38 +10:00
parent 26df4f4bc8
commit 42dc003e91
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3 changed files with 61 additions and 17 deletions
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36
specs/core/0_beacon-chain.md
View File

@ -316,6 +316,8 @@ The types are defined topologically to aid in facilitating an executable version
'epoch': 'uint64',
# Shard data since the previous crosslink
'crosslink_data_root': 'bytes32',
# Root of the previous crosslink
'previous_crosslink_root': 'bytes32',
}
```
@ -358,7 +360,7 @@ The types are defined topologically to aid in facilitating an executable version
# Crosslink vote
'shard': 'uint64',
'source_crosslink': Crosslink,
'source_crosslink_root': 'bytes32',
'crosslink_data_root': 'bytes32',
}
```
@ -1565,8 +1567,8 @@ def get_genesis_beacon_state(genesis_validator_deposits: List[Deposit],
finalized_root=ZERO_HASH,
# Recent state
current_crosslinks=Vector([Crosslink(epoch=GENESIS_EPOCH, crosslink_data_root=ZERO_HASH) for _ in range(SHARD_COUNT)]),
previous_crosslinks=Vector([Crosslink(epoch=GENESIS_EPOCH, crosslink_data_root=ZERO_HASH) for _ in range(SHARD_COUNT)]),
current_crosslinks=Vector([Crosslink(epoch=GENESIS_EPOCH, crosslink_data_root=ZERO_HASH, previous_crosslink_root=ZERO_HASH) for _ in range(SHARD_COUNT)]),
previous_crosslinks=Vector([Crosslink(epoch=GENESIS_EPOCH, crosslink_data_root=ZERO_HASH, previous_crosslink_root=ZERO_HASH) for _ in range(SHARD_COUNT)]),
latest_block_roots=Vector([ZERO_HASH for _ in range(SLOTS_PER_HISTORICAL_ROOT)]),
latest_state_roots=Vector([ZERO_HASH for _ in range(SLOTS_PER_HISTORICAL_ROOT)]),
latest_active_index_roots=Vector([ZERO_HASH for _ in range(LATEST_ACTIVE_INDEX_ROOTS_LENGTH)]),
@ -1771,24 +1773,28 @@ def get_previous_epoch_matching_head_attestations(state: BeaconState) -> List[Pe
**Note**: Total balances computed for the previous epoch might be marginally different than the actual total balances during the previous epoch transition. Due to the tight bound on validator churn each epoch and small per-epoch rewards/penalties, the potential balance difference is very low and only marginally affects consensus safety.
```python
def get_winning_root_and_participants(state: BeaconState, slot: Slot, shard: Shard) -> Tuple[Bytes32, List[ValidatorIndex]]:
def get_winning_root_and_participants(state: BeaconState, slot: Slot, shard: Shard) -> Tuple[Bytes32, Bytes32, List[ValidatorIndex]]:
attestations = state.current_epoch_attestations if slot_to_epoch(slot) == get_current_epoch(state) else state.previous_epoch_attestations
valid_attestations = [a for a in attestations if a.data.shard == shard]
all_roots = [a.data.crosslink_data_root for a in valid_attestations]
all_roots = [(a.data.crosslink_data_root, a.data.source_crosslink_root) for a in valid_attestations]
# handle when no attestations for shard available
if len(all_roots) == 0:
return ZERO_HASH, []
return ZERO_HASH, ZERO_HASH, []
def get_attestations_for(root) -> List[PendingAttestation]:
return [a for a in valid_attestations if a.data.crosslink_data_root == root]
# Winning crosslink root is the root with the most votes for it, ties broken in favor of
# lexicographically higher hash
winning_root = max(all_roots, key=lambda r: (get_attesting_balance(state, get_attestations_for(r)), r))
winning_root, previous_crosslink_root = max(all_roots, key=lambda r: (get_attesting_balance(state, get_attestations_for(r[0])), r[0]))
return winning_root, get_attesting_indices(state, get_attestations_for(winning_root))
return (
winning_root,
previous_crosslink_root,
get_attesting_indices(state, get_attestations_for(winning_root)),
)
```
```python
@ -1873,13 +1879,15 @@ def process_crosslinks(state: BeaconState) -> None:
for slot in range(get_epoch_start_slot(previous_epoch), get_epoch_start_slot(next_epoch)):
for crosslink_committee, shard in get_crosslink_committees_at_slot(state, slot):
winning_root, participants = get_winning_root_and_participants(state, slot, shard)
winning_root, previous_crosslink_root, participants = get_winning_root_and_participants(state, slot, shard)
expected_crosslink_root = hash_tree_root(state.current_crosslinks[shard])
participating_balance = get_total_balance(state, participants)
total_balance = get_total_balance(state, crosslink_committee)
if 3 * participating_balance >= 2 * total_balance:
if previous_crosslink_root == expected_crosslink_root and 3 * participating_balance >= 2 * total_balance:
state.current_crosslinks[shard] = Crosslink(
epoch=min(slot_to_epoch(slot), state.current_crosslinks[shard].epoch + MAX_CROSSLINK_EPOCHS),
crosslink_data_root=winning_root,
previous_crosslink_root=previous_crosslink_root,
)
```
@ -1987,7 +1995,7 @@ def get_crosslink_deltas(state: BeaconState) -> Tuple[List[Gwei], List[Gwei]]:
current_epoch_start_slot = get_epoch_start_slot(get_current_epoch(state))
for slot in range(previous_epoch_start_slot, current_epoch_start_slot):
for crosslink_committee, shard in get_crosslink_committees_at_slot(state, slot):
winning_root, participants = get_winning_root_and_participants(state, slot, shard)
winning_root, _, participants = get_winning_root_and_participants(state, slot, shard)
participating_balance = get_total_balance(state, participants)
total_balance = get_total_balance(state, crosslink_committee)
for index in crosslink_committee:
@ -2338,9 +2346,9 @@ def process_attestation(state: BeaconState, attestation: Attestation) -> None:
# Check target epoch, source epoch, source root, and source crosslink
target_epoch = slot_to_epoch(data.slot)
assert (target_epoch, data.source_epoch, data.source_root, data.source_crosslink) in {
(get_current_epoch(state), state.current_justified_epoch, state.current_justified_root, state.current_crosslinks[data.shard]),
(get_previous_epoch(state), state.previous_justified_epoch, state.previous_justified_root, state.previous_crosslinks[data.shard]),
assert (target_epoch, data.source_epoch, data.source_root, data.source_crosslink_root) in {
(get_current_epoch(state), state.current_justified_epoch, state.current_justified_root, hash_tree_root(state.current_crosslinks[data.shard])),
(get_previous_epoch(state), state.previous_justified_epoch, state.previous_justified_root, hash_tree_root(state.previous_crosslinks[data.shard])),
}
# Check crosslink data root

39
tests/phase0/epoch_processing/test_process_crosslinks.py
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@ -29,8 +29,6 @@ pytestmark = pytest.mark.crosslinks
def run_process_crosslinks(state, valid=True):
post_state = deepcopy(state)
# transition state to slot before state transition
slot = state.slot + (spec.SLOTS_PER_EPOCH - state.slot % spec.SLOTS_PER_EPOCH) - 1
block = build_empty_block_for_next_slot(state)
@ -40,6 +38,7 @@ def run_process_crosslinks(state, valid=True):
# cache state before epoch transition
cache_state(state)
post_state = deepcopy(state)
process_crosslinks(post_state)
return state, post_state
@ -90,3 +89,39 @@ def test_single_crosslink_update_from_previous_epoch(state):
assert pre_state.current_crosslinks[shard] != post_state.current_crosslinks[shard]
return pre_state, post_state
def test_double_late_crosslink(state):
next_epoch(state)
state.slot += 4
attestation_1 = get_valid_attestation(state)
fill_aggregate_attestation(state, attestation_1)
# add attestation_1 in the next epoch
next_epoch(state)
add_attestation_to_state(state, attestation_1, state.slot + 1)
state.slot = attestation_1.data.slot + spec.SLOTS_PER_EPOCH
attestation_2 = get_valid_attestation(state)
fill_aggregate_attestation(state, attestation_2)
# add attestation_2 in the next epoch after attestation_1 has
# already updated the relevant crosslink
next_epoch(state)
add_attestation_to_state(state, attestation_2, state.slot + 1)
assert len(state.previous_epoch_attestations) == 1
assert len(state.current_epoch_attestations) == 0
pre_state, post_state = run_process_crosslinks(state)
shard_1 = attestation_1.data.shard
shard_2 = attestation_2.data.shard
assert shard_1 == shard_2
shard = shard_1
# ensure that the current crosslinks were not updated by the second attestation
assert post_state.previous_crosslinks[shard] == post_state.current_crosslinks[shard]
return pre_state, post_state

3
tests/phase0/helpers.py
View File

@ -34,6 +34,7 @@ from build.phase0.spec import (
get_empty_block,
get_epoch_start_slot,
get_genesis_beacon_state,
hash_tree_root,
slot_to_epoch,
verify_merkle_branch,
hash,
@ -172,7 +173,7 @@ def build_attestation_data(state, slot, shard):
source_root=justified_block_root,
target_root=epoch_boundary_root,
crosslink_data_root=spec.ZERO_HASH,
source_crosslink=deepcopy(crosslinks[shard]),
source_crosslink_root=hash_tree_root(crosslinks[shard]),
)