Merge pull request #2406 from ethereum/sync-seed

remove sync committee seed and restrict period calculation boundaries

specs/altair/beacon-chain.md

@@ -32,8 +32,8 @@
     - [`add_flag`](#add_flag)
     - [`has_flag`](#has_flag)
   - [Beacon state accessors](#beacon-state-accessors)
-    - [`get_sync_committee_indices`](#get_sync_committee_indices)
+    - [`get_next_sync_committee_indices`](#get_next_sync_committee_indices)
-    - [`get_sync_committee`](#get_sync_committee)
+    - [`get_next_sync_committee`](#get_next_sync_committee)
     - [`get_base_reward_per_increment`](#get_base_reward_per_increment)
     - [`get_base_reward`](#get_base_reward)
     - [`get_unslashed_participating_indices`](#get_unslashed_participating_indices)
@@ -270,22 +270,20 @@ def has_flag(flags: ParticipationFlags, flag_index: int) -> bool:
 
 ### Beacon state accessors
 
-#### `get_sync_committee_indices`
+#### `get_next_sync_committee_indices`
 
 ```python
-def get_sync_committee_indices(state: BeaconState, epoch: Epoch) -> Sequence[ValidatorIndex]:
+def get_next_sync_committee_indices(state: BeaconState) -> Sequence[ValidatorIndex]:
     """
     Return the sequence of sync committee indices (which may include duplicate indices)
-    for a given ``state`` and ``epoch``.
+    for the next sync committee, given a ``state`` at a sync committee period boundary.
-
-    Note: This function is not stable during a sync committee period as
-    a validator's effective balance may change enough to affect the sampling.
     """
+    epoch = Epoch(get_current_epoch(state) + 1)
+
     MAX_RANDOM_BYTE = 2**8 - 1
-    base_epoch = Epoch((max(epoch // EPOCHS_PER_SYNC_COMMITTEE_PERIOD, 1) - 1) * EPOCHS_PER_SYNC_COMMITTEE_PERIOD)
+    active_validator_indices = get_active_validator_indices(state, epoch)
-    active_validator_indices = get_active_validator_indices(state, base_epoch)
     active_validator_count = uint64(len(active_validator_indices))
-    seed = get_seed(state, base_epoch, DOMAIN_SYNC_COMMITTEE)
+    seed = get_seed(state, epoch, DOMAIN_SYNC_COMMITTEE)
     i = 0
     sync_committee_indices: List[ValidatorIndex] = []
     while len(sync_committee_indices) < SYNC_COMMITTEE_SIZE:
@@ -299,25 +297,25 @@ def get_sync_committee_indices(state: BeaconState, epoch: Epoch) -> Sequence[Val
     return sync_committee_indices
 ```
 
-#### `get_sync_committee`
+#### `get_next_sync_committee`
 
 ```python
-def get_sync_committee(state: BeaconState, epoch: Epoch) -> SyncCommittee:
+def get_next_sync_committee(state: BeaconState) -> SyncCommittee:
     """
-    Return the sync committee for a given ``state`` and ``epoch``.
+    Return the *next* sync committee for a given ``state``.
 
     ``SyncCommittee`` contains an aggregate pubkey that enables
     resource-constrained clients to save some computation when verifying
     the sync committee's signature.
 
-    ``SyncCommittee`` can also contain duplicate pubkeys, when ``get_sync_committee_indices``
+    ``SyncCommittee`` can also contain duplicate pubkeys, when ``get_next_sync_committee_indices``
     returns duplicate indices. Implementations must take care when handling
     optimizations relating to aggregation and verification in the presence of duplicates.
 
     Note: This function should only be called at sync committee period boundaries, as
-    ``get_sync_committee_indices`` is not stable within a given period.
+    ``get_next_sync_committee_indices`` is not stable within a given period.
     """
-    indices = get_sync_committee_indices(state, epoch)
+    indices = get_next_sync_committee_indices(state)
     pubkeys = [state.validators[index].pubkey for index in indices]
     aggregate_pubkey = bls.AggregatePKs(pubkeys)
     return SyncCommittee(pubkeys=pubkeys, aggregate_pubkey=aggregate_pubkey)
@@ -690,7 +688,7 @@ def process_sync_committee_updates(state: BeaconState) -> None:
     next_epoch = get_current_epoch(state) + Epoch(1)
     if next_epoch % EPOCHS_PER_SYNC_COMMITTEE_PERIOD == 0:
         state.current_sync_committee = state.next_sync_committee
-        state.next_sync_committee = get_sync_committee(state, next_epoch + EPOCHS_PER_SYNC_COMMITTEE_PERIOD)
+        state.next_sync_committee = get_next_sync_committee(state)
 ```
 
 ## Initialize state for pure Altair testnets and test vectors
@@ -735,8 +733,9 @@ def initialize_beacon_state_from_eth1(eth1_block_hash: Bytes32,
     state.genesis_validators_root = hash_tree_root(state.validators)
 
     # [New in Altair] Fill in sync committees
-    state.current_sync_committee = get_sync_committee(state, get_current_epoch(state))
+    # Note: A duplicate committee is assigned for the current and next committee at genesis
-    state.next_sync_committee = get_sync_committee(state, get_current_epoch(state) + EPOCHS_PER_SYNC_COMMITTEE_PERIOD)
+    state.current_sync_committee = get_next_sync_committee(state)
+    state.next_sync_committee = get_next_sync_committee(state)
 
     return state
 ```

specs/altair/fork.md

@@ -84,8 +84,10 @@ def upgrade_to_altair(pre: phase0.BeaconState) -> BeaconState:
         # Inactivity
         inactivity_scores=[uint64(0) for _ in range(len(pre.validators))],
     )
+
     # Fill in sync committees
-    post.current_sync_committee = get_sync_committee(post, get_current_epoch(post))
+    # Note: A duplicate committee is assigned for the current and next committee at the fork boundary
-    post.next_sync_committee = get_sync_committee(post, get_current_epoch(post) + EPOCHS_PER_SYNC_COMMITTEE_PERIOD)
+    post.current_sync_committee = get_next_sync_committee(post)
+    post.next_sync_committee = get_next_sync_committee(post)
     return post
 ```

tests/core/pyspec/eth2spec/test/altair/block_processing/test_process_sync_committee.py

@@ -7,7 +7,6 @@ from eth2spec.test.helpers.block_processing import run_block_processing_to
 from eth2spec.test.helpers.state import (
     state_transition_and_sign_block,
     transition_to,
-    next_epoch,
 )
 from eth2spec.test.helpers.constants import (
     MAINNET, MINIMAL,
@@ -50,9 +49,9 @@ def get_committee_indices(spec, state, duplicates=False):
     """
     state = state.copy()
     current_epoch = spec.get_current_epoch(state)
-    randao_index = current_epoch % spec.EPOCHS_PER_HISTORICAL_VECTOR
+    randao_index = (current_epoch + 1) % spec.EPOCHS_PER_HISTORICAL_VECTOR
     while True:
-        committee = spec.get_sync_committee_indices(state, spec.get_current_epoch(state))
+        committee = spec.get_next_sync_committee_indices(state)
         if duplicates:
             if len(committee) != len(set(committee)):
                 return committee
@@ -62,23 +61,32 @@ def get_committee_indices(spec, state, duplicates=False):
         state.randao_mixes[randao_index] = hash(state.randao_mixes[randao_index])
 
 
+def compute_committee_indices(spec, state, committee):
+    """
+    Given a ``committee``, calculate and return the related indices
+    """
+    all_pubkeys = [v.pubkey for v in state.validators]
+    committee_indices = [all_pubkeys.index(pubkey) for pubkey in committee.pubkeys]
+    return committee_indices
+
+
 @with_altair_and_later
 @spec_state_test
 @always_bls
 def test_invalid_signature_missing_participant(spec, state):
-    committee = spec.get_sync_committee_indices(state, spec.get_current_epoch(state))
+    committee_indices = compute_committee_indices(spec, state, state.current_sync_committee)
     rng = random.Random(2020)
-    random_participant = rng.choice(committee)
+    random_participant = rng.choice(committee_indices)
 
     block = build_empty_block_for_next_slot(spec, state)
     # Exclude one participant whose signature was included.
     block.body.sync_aggregate = spec.SyncAggregate(
-        sync_committee_bits=[index != random_participant for index in committee],
+        sync_committee_bits=[index != random_participant for index in committee_indices],
         sync_committee_signature=compute_aggregate_sync_committee_signature(
             spec,
             state,
             block.slot - 1,
-            committee,  # full committee signs
+            committee_indices,  # full committee signs
         )
     )
     yield from run_sync_committee_processing(spec, state, block, expect_exception=True)
@@ -88,31 +96,38 @@ def test_invalid_signature_missing_participant(spec, state):
 @spec_state_test
 @always_bls
 def test_invalid_signature_extra_participant(spec, state):
-    committee = spec.get_sync_committee_indices(state, spec.get_current_epoch(state))
+    committee_indices = compute_committee_indices(spec, state, state.current_sync_committee)
     rng = random.Random(3030)
-    random_participant = rng.choice(committee)
+    random_participant = rng.choice(committee_indices)
 
     block = build_empty_block_for_next_slot(spec, state)
     # Exclude one signature even though the block claims the entire committee participated.
     block.body.sync_aggregate = spec.SyncAggregate(
-        sync_committee_bits=[True] * len(committee),
+        sync_committee_bits=[True] * len(committee_indices),
         sync_committee_signature=compute_aggregate_sync_committee_signature(
             spec,
             state,
             block.slot - 1,
-            [index for index in committee if index != random_participant],
+            [index for index in committee_indices if index != random_participant],
         )
     )
 
     yield from run_sync_committee_processing(spec, state, block, expect_exception=True)
 
 
-def compute_sync_committee_inclusion_reward(spec, state, participant_index, committee, committee_bits):
+def compute_sync_committee_inclusion_reward(spec,
+                                            state,
+                                            participant_index,
+                                            committee_indices,
+                                            committee_bits):
     total_active_increments = spec.get_total_active_balance(state) // spec.EFFECTIVE_BALANCE_INCREMENT
     total_base_rewards = spec.Gwei(spec.get_base_reward_per_increment(state) * total_active_increments)
     max_epoch_rewards = spec.Gwei(total_base_rewards * spec.SYNC_REWARD_WEIGHT // spec.WEIGHT_DENOMINATOR)
-    included_indices = [index for index, bit in zip(committee, committee_bits) if bit]
+    included_indices = [index for index, bit in zip(committee_indices, committee_bits) if bit]
-    max_slot_rewards = spec.Gwei(max_epoch_rewards * len(included_indices) // len(committee) // spec.SLOTS_PER_EPOCH)
+    max_slot_rewards = spec.Gwei(
+        max_epoch_rewards * len(included_indices)
+        // len(committee_indices) // spec.SLOTS_PER_EPOCH
+    )
 
     # Compute the participant and proposer sync rewards
     committee_effective_balance = sum([state.validators[index].effective_balance for index in included_indices])
@@ -121,23 +136,23 @@ def compute_sync_committee_inclusion_reward(spec, state, participant_index, comm
     return spec.Gwei(max_slot_rewards * effective_balance // committee_effective_balance)
 
 
-def compute_sync_committee_participant_reward(spec, state, participant_index, committee, committee_bits):
+def compute_sync_committee_participant_reward(spec, state, participant_index, committee_indices, committee_bits):
-    included_indices = [index for index, bit in zip(committee, committee_bits) if bit]
+    included_indices = [index for index, bit in zip(committee_indices, committee_bits) if bit]
     multiplicities = Counter(included_indices)
 
     inclusion_reward = compute_sync_committee_inclusion_reward(
-        spec, state, participant_index, committee, committee_bits,
+        spec, state, participant_index, committee_indices, committee_bits,
     )
     return spec.Gwei(inclusion_reward * multiplicities[participant_index])
 
 
-def compute_sync_committee_proposer_reward(spec, state, committee, committee_bits):
+def compute_sync_committee_proposer_reward(spec, state, committee_indices, committee_bits):
     proposer_reward = 0
-    for index, bit in zip(committee, committee_bits):
+    for index, bit in zip(committee_indices, committee_bits):
         if not bit:
             continue
         inclusion_reward = compute_sync_committee_inclusion_reward(
-            spec, state, index, committee, committee_bits,
+            spec, state, index, committee_indices, committee_bits,
         )
         proposer_reward_denominator = (
             (spec.WEIGHT_DENOMINATOR - spec.PROPOSER_WEIGHT)
@@ -148,15 +163,15 @@ def compute_sync_committee_proposer_reward(spec, state, committee, committee_bit
     return proposer_reward
 
 
-def validate_sync_committee_rewards(spec, pre_state, post_state, committee, committee_bits, proposer_index):
+def validate_sync_committee_rewards(spec, pre_state, post_state, committee_indices, committee_bits, proposer_index):
     for index in range(len(post_state.validators)):
         reward = 0
-        if index in committee:
+        if index in committee_indices:
             reward += compute_sync_committee_participant_reward(
                 spec,
                 pre_state,
                 index,
-                committee,
+                committee_indices,
                 committee_bits,
             )
 
@@ -164,14 +179,14 @@ def validate_sync_committee_rewards(spec, pre_state, post_state, committee, comm
             reward += compute_sync_committee_proposer_reward(
                 spec,
                 pre_state,
-                committee,
+                committee_indices,
                 committee_bits,
             )
 
         assert post_state.balances[index] == pre_state.balances[index] + reward
 
 
-def run_successful_sync_committee_test(spec, state, committee, committee_bits):
+def run_successful_sync_committee_test(spec, state, committee_indices, committee_bits):
     pre_state = state.copy()
 
     block = build_empty_block_for_next_slot(spec, state)
@@ -181,7 +196,7 @@ def run_successful_sync_committee_test(spec, state, committee, committee_bits):
             spec,
             state,
             block.slot - 1,
-            [index for index, bit in zip(committee, committee_bits) if bit],
+            [index for index, bit in zip(committee_indices, committee_bits) if bit],
         )
     )
 
@@ -191,7 +206,7 @@ def run_successful_sync_committee_test(spec, state, committee, committee_bits):
         spec,
         pre_state,
         state,
-        committee,
+        committee_indices,
         committee_bits,
         block.proposer_index,
     )
@@ -201,60 +216,60 @@ def run_successful_sync_committee_test(spec, state, committee, committee_bits):
 @with_configs([MINIMAL], reason="to create nonduplicate committee")
 @spec_state_test
 def test_sync_committee_rewards_nonduplicate_committee(spec, state):
-    committee = get_committee_indices(spec, state, duplicates=False)
+    committee_indices = get_committee_indices(spec, state, duplicates=False)
-    committee_size = len(committee)
+    committee_size = len(committee_indices)
     committee_bits = [True] * committee_size
     active_validator_count = len(spec.get_active_validator_indices(state, spec.get_current_epoch(state)))
 
     # Preconditions of this test case
     assert active_validator_count >= spec.SYNC_COMMITTEE_SIZE
-    assert committee_size == len(set(committee))
+    assert committee_size == len(set(committee_indices))
 
-    yield from run_successful_sync_committee_test(spec, state, committee, committee_bits)
+    yield from run_successful_sync_committee_test(spec, state, committee_indices, committee_bits)
 
 
 @with_altair_and_later
 @with_configs([MAINNET], reason="to create duplicate committee")
 @spec_state_test
 def test_sync_committee_rewards_duplicate_committee(spec, state):
-    committee = get_committee_indices(spec, state, duplicates=True)
+    committee_indices = get_committee_indices(spec, state, duplicates=True)
-    committee_size = len(committee)
+    committee_size = len(committee_indices)
     committee_bits = [True] * committee_size
     active_validator_count = len(spec.get_active_validator_indices(state, spec.get_current_epoch(state)))
 
     # Preconditions of this test case
     assert active_validator_count < spec.SYNC_COMMITTEE_SIZE
-    assert committee_size > len(set(committee))
+    assert committee_size > len(set(committee_indices))
 
-    yield from run_successful_sync_committee_test(spec, state, committee, committee_bits)
+    yield from run_successful_sync_committee_test(spec, state, committee_indices, committee_bits)
 
 
 @with_altair_and_later
 @spec_state_test
 @always_bls
 def test_sync_committee_rewards_not_full_participants(spec, state):
-    committee = spec.get_sync_committee_indices(state, spec.get_current_epoch(state))
+    committee_indices = compute_committee_indices(spec, state, state.current_sync_committee)
     rng = random.Random(1010)
-    committee_bits = [rng.choice([True, False]) for _ in committee]
+    committee_bits = [rng.choice([True, False]) for _ in committee_indices]
 
-    yield from run_successful_sync_committee_test(spec, state, committee, committee_bits)
+    yield from run_successful_sync_committee_test(spec, state, committee_indices, committee_bits)
 
 
 @with_altair_and_later
 @spec_state_test
 @always_bls
 def test_sync_committee_rewards_empty_participants(spec, state):
-    committee = spec.get_sync_committee_indices(state, spec.get_current_epoch(state))
+    committee_indices = compute_committee_indices(spec, state, state.current_sync_committee)
-    committee_bits = [False for _ in committee]
+    committee_bits = [False for _ in committee_indices]
 
-    yield from run_successful_sync_committee_test(spec, state, committee, committee_bits)
+    yield from run_successful_sync_committee_test(spec, state, committee_indices, committee_bits)
 
 
 @with_altair_and_later
 @spec_state_test
 @always_bls
 def test_invalid_signature_past_block(spec, state):
-    committee = spec.get_sync_committee_indices(state, spec.get_current_epoch(state))
+    committee_indices = compute_committee_indices(spec, state, state.current_sync_committee)
 
     blocks = []
     for _ in range(2):
@@ -262,12 +277,12 @@ def test_invalid_signature_past_block(spec, state):
         block = build_empty_block_for_next_slot(spec, state)
         # Valid sync committee signature here...
         block.body.sync_aggregate = spec.SyncAggregate(
-            sync_committee_bits=[True] * len(committee),
+            sync_committee_bits=[True] * len(committee_indices),
             sync_committee_signature=compute_aggregate_sync_committee_signature(
                 spec,
                 state,
                 block.slot - 1,
-                committee,
+                committee_indices,
             )
         )
 
@@ -277,12 +292,12 @@ def test_invalid_signature_past_block(spec, state):
     invalid_block = build_empty_block_for_next_slot(spec, state)
     # Invalid signature from a slot other than the previous
     invalid_block.body.sync_aggregate = spec.SyncAggregate(
-        sync_committee_bits=[True] * len(committee),
+        sync_committee_bits=[True] * len(committee_indices),
         sync_committee_signature=compute_aggregate_sync_committee_signature(
             spec,
             state,
             invalid_block.slot - 2,
-            committee,
+            committee_indices,
         )
     )
 
@@ -307,19 +322,18 @@ def test_invalid_signature_previous_committee(spec, state):
     transition_to(spec, state, slot_in_future_sync_committee_period)
 
     # Use the previous sync committee to produce the signature.
-    pubkeys = [validator.pubkey for validator in state.validators]
     # Ensure that the pubkey sets are different.
     assert set(old_sync_committee.pubkeys) != set(state.current_sync_committee.pubkeys)
-    committee = [pubkeys.index(pubkey) for pubkey in old_sync_committee.pubkeys]
+    committee_indices = compute_committee_indices(spec, state, old_sync_committee)
 
     block = build_empty_block_for_next_slot(spec, state)
     block.body.sync_aggregate = spec.SyncAggregate(
-        sync_committee_bits=[True] * len(committee),
+        sync_committee_bits=[True] * len(committee_indices),
         sync_committee_signature=compute_aggregate_sync_committee_signature(
             spec,
             state,
             block.slot - 1,
-            committee,
+            committee_indices,
         )
     )
 
@@ -345,15 +359,13 @@ def test_valid_signature_future_committee(spec, state):
     transition_to(spec, state, slot_in_future_sync_committee_period)
 
     sync_committee = state.current_sync_committee
+    next_sync_committee = state.next_sync_committee
 
-    expected_sync_committee = spec.get_sync_committee(state, epoch_in_future_sync_committee_period)
+    assert next_sync_committee != sync_committee
-
-    assert sync_committee == expected_sync_committee
     assert sync_committee != old_current_sync_committee
     assert sync_committee != old_next_sync_committee
 
-    pubkeys = [validator.pubkey for validator in state.validators]
+    committee_indices = compute_committee_indices(spec, state, sync_committee)
-    committee_indices = [pubkeys.index(pubkey) for pubkey in sync_committee.pubkeys]
 
     block = build_empty_block_for_next_slot(spec, state)
     block.body.sync_aggregate = spec.SyncAggregate(
@@ -367,43 +379,3 @@ def test_valid_signature_future_committee(spec, state):
     )
 
     yield from run_sync_committee_processing(spec, state, block)
-
-
-@with_altair_and_later
-@spec_state_test
-def test_sync_committee_is_only_computed_at_epoch_boundary(spec, state):
-    """
-    Sync committees can only be computed at sync committee period boundaries.
-    Ensure a client respects the committee in the state (assumed to be derived
-    in the correct way).
-    """
-    current_epoch = spec.get_current_epoch(state)
-
-    # use a "synthetic" committee to simulate the situation
-    # where ``spec.get_sync_committee`` at the sync committee
-    # period epoch boundary would have diverged some epochs into the
-    # period; ``aggregate_pubkey`` is not relevant to this test
-    pubkeys = []
-    committee_indices = []
-    i = 0
-    active_validator_count = len(spec.get_active_validator_indices(state, current_epoch))
-    while len(pubkeys) < spec.SYNC_COMMITTEE_SIZE:
-        v = state.validators[i % active_validator_count]
-        if spec.is_active_validator(v, current_epoch):
-            pubkeys.append(v.pubkey)
-            committee_indices.append(i)
-        i += 1
-
-    synthetic_committee = spec.SyncCommittee(pubkeys=pubkeys, aggregate_pubkey=spec.BLSPubkey())
-    state.current_sync_committee = synthetic_committee
-
-    assert spec.EPOCHS_PER_SYNC_COMMITTEE_PERIOD > 3
-    for _ in range(3):
-        next_epoch(spec, state)
-
-    committee = get_committee_indices(spec, state)
-    assert committee != committee_indices
-    committee_size = len(committee_indices)
-    committee_bits = [True] * committee_size
-
-    yield from run_successful_sync_committee_test(spec, state, committee_indices, committee_bits)

tests/core/pyspec/eth2spec/test/altair/epoch_processing/test_process_sync_committee_updates.py

@@ -39,8 +39,7 @@ def run_sync_committees_progress_test(spec, state):
 
     # Can compute the third committee having computed final balances in the last epoch
     # of this `EPOCHS_PER_SYNC_COMMITTEE_PERIOD`
-    current_epoch = spec.get_current_epoch(state)
+    third_sync_committee = spec.get_next_sync_committee(state)
-    third_sync_committee = spec.get_sync_committee(state, current_epoch + 2 * spec.EPOCHS_PER_SYNC_COMMITTEE_PERIOD)
 
     assert state.current_sync_committee == second_sync_committee
     assert state.next_sync_committee == third_sync_committee

tests/core/pyspec/eth2spec/test/altair/sanity/test_blocks.py

@@ -18,7 +18,8 @@ from eth2spec.test.context import (
 
 
 def run_sync_committee_sanity_test(spec, state, fraction_full=1.0):
-    committee = spec.get_sync_committee_indices(state, spec.get_current_epoch(state))
+    all_pubkeys = [v.pubkey for v in state.validators]
+    committee = [all_pubkeys.index(pubkey) for pubkey in state.current_sync_committee.pubkeys]
     participants = random.sample(committee, int(len(committee) * fraction_full))
 
     yield 'pre', state

tests/core/pyspec/eth2spec/test/altair/unittests/test_sync_protocol.py

@@ -46,7 +46,8 @@ def test_process_light_client_update_not_updated(spec, state):
         body_root=signed_block.message.body.hash_tree_root(),
     )
     # Sync committee signing the header
-    committee = spec.get_sync_committee_indices(state, spec.get_current_epoch(state))
+    all_pubkeys = [v.pubkey for v in state.validators]
+    committee = [all_pubkeys.index(pubkey) for pubkey in state.current_sync_committee.pubkeys]
     sync_committee_bits = [True] * len(committee)
     sync_committee_signature = compute_aggregate_sync_committee_signature(
         spec,
@@ -111,7 +112,8 @@ def test_process_light_client_update_timeout(spec, state):
     )
 
     # Sync committee signing the finalized_block_header
-    committee = spec.get_sync_committee_indices(state, spec.get_current_epoch(state))
+    all_pubkeys = [v.pubkey for v in state.validators]
+    committee = [all_pubkeys.index(pubkey) for pubkey in state.current_sync_committee.pubkeys]
     sync_committee_bits = [True] * len(committee)
     sync_committee_signature = compute_aggregate_sync_committee_signature(
         spec,
@@ -190,7 +192,8 @@ def test_process_light_client_update_finality_updated(spec, state):
     )
 
     # Sync committee signing the finalized_block_header
-    committee = spec.get_sync_committee_indices(state, spec.get_current_epoch(state))
+    all_pubkeys = [v.pubkey for v in state.validators]
+    committee = [all_pubkeys.index(pubkey) for pubkey in state.current_sync_committee.pubkeys]
     sync_committee_bits = [True] * len(committee)
     sync_committee_signature = compute_aggregate_sync_committee_signature(
         spec,

tests/core/pyspec/eth2spec/test/helpers/genesis.py

@@ -69,9 +69,8 @@ def create_genesis_state(spec, validator_balances, activation_threshold):
 
     if spec.fork not in FORKS_BEFORE_ALTAIR:
         # Fill in sync committees
-        state.current_sync_committee = spec.get_sync_committee(state, spec.get_current_epoch(state))
+        # Note: A duplicate committee is assigned for the current and next committee at genesis
-        state.next_sync_committee = (
+        state.current_sync_committee = spec.get_next_sync_committee(state)
-            spec.get_sync_committee(state, spec.get_current_epoch(state) + spec.EPOCHS_PER_SYNC_COMMITTEE_PERIOD)
+        state.next_sync_committee = spec.get_next_sync_committee(state)
-        )
 
     return state