Update randomness-related fields

1. Add constants: `LATEST_RANDAO_MIXES_LENGTH`
2. Update `BeaconState` fields.
```
-        ('randao_mix', hash32),
-        ('next_seed', hash32),
+        ('latest_randao_mixes', CountableList(hash32)),
+        ('latest_vdf_outputs', CountableList(hash32)),
```

Author: hwwhww

eth/beacon/state_machines/configs.py

@@ -19,6 +19,7 @@
         ('BLS_WITHDRAWAL_PREFIX_BYTE', bytes),
         ('MAX_CASPER_VOTES', int),
         ('LATEST_BLOCK_ROOTS_LENGTH', int),
+        ('LATEST_RANDAO_MIXES_LENGTH', int),
         # EMPTY_SIGNATURE is defined in constants.py
         # Deposit contract
         ('DEPOSIT_CONTRACT_ADDRESS', Address),

eth/beacon/state_machines/forks/serenity/configs.py

@@ -14,6 +14,7 @@
     BLS_WITHDRAWAL_PREFIX_BYTE=b'\x00',
     MAX_CASPER_VOTES=2**10,  # (= 1,024) votes
     LATEST_BLOCK_ROOTS_LENGTH=2**13,  # (= 8,192) block roots
+    LATEST_RANDAO_MIXES_LENGTH=2**13,  # (= 8,192) randao mixes
     # Deposit contract
     DEPOSIT_CONTRACT_ADDRESS=ZERO_ADDRESS,  # TBD
     DEPOSIT_CONTRACT_TREE_DEPTH=2**5,  # (= 32)

eth/beacon/types/states.py

@@ -50,8 +50,8 @@ class BeaconState(rlp.Serializable):
         ('validator_registry_delta_chain_tip', hash32),  # For light clients to easily track delta
 
         # Randomness and committees
-        ('randao_mix', hash32),
-        ('next_seed', hash32),
+        ('latest_randao_mixes', CountableList(hash32)),
+        ('latest_vdf_outputs', CountableList(hash32)),
         ('shard_committees_at_slots', CountableList(CountableList((ShardCommittee)))),
         ('persistent_committees', CountableList(CountableList(uint24))),
         ('persistent_committee_reassignments', CountableList(ShardReassignmentRecord)),
@@ -82,15 +82,15 @@ def __init__(
             validator_registry_latest_change_slot: int,
             validator_registry_exit_count: int,
             validator_registry_delta_chain_tip: Hash32,
-            randao_mix: Hash32,
-            next_seed: Hash32,
             previous_justified_slot: int,
             justified_slot: int,
             justification_bitfield: int,
             finalized_slot: int,
             processed_pow_receipt_root: Hash32,
             validator_registry: Sequence[ValidatorRecord]=(),
             validator_balances: Sequence[int]=(),
+            latest_randao_mixes: Sequence[Hash32]=(),
+            latest_vdf_outputs: Sequence[Hash32]=(),
             shard_committees_at_slots: Sequence[Sequence[ShardCommittee]]=(),
             persistent_committees: Sequence[Sequence[int]]=(),
             persistent_committee_reassignments: Sequence[ShardReassignmentRecord]=(),
@@ -113,8 +113,8 @@ def __init__(
             validator_registry_exit_count=validator_registry_exit_count,
             validator_registry_delta_chain_tip=validator_registry_delta_chain_tip,
             # Randomness and committees
-            randao_mix=randao_mix,
-            next_seed=next_seed,
+            latest_randao_mixes=latest_randao_mixes,
+            latest_vdf_outputs=latest_vdf_outputs,
             shard_committees_at_slots=shard_committees_at_slots,
             persistent_committees=persistent_committees,
             persistent_committee_reassignments=persistent_committee_reassignments,

tests/beacon/conftest.py

@@ -133,8 +133,8 @@ def sample_beacon_state_params(sample_fork_data_params):
         'validator_registry_latest_change_slot': 10,
         'validator_registry_exit_count': 10,
         'validator_registry_delta_chain_tip': b'\x55' * 32,
-        'randao_mix': b'\x55' * 32,
-        'next_seed': b'\x55' * 32,
+        'latest_randao_mixes': (),
+        'latest_vdf_outputs': (),
         'shard_committees_at_slots': (),
         'persistent_committees': (),
         'persistent_committee_reassignments': (),
@@ -368,6 +368,11 @@ def latest_block_roots_length():
     return SERENITY_CONFIG.LATEST_BLOCK_ROOTS_LENGTH
 
 
+@pytest.fixture
+def latest_randao_mixes_length():
+    return SERENITY_CONFIG.LATEST_RANDAO_MIXES_LENGTH
+
+
 @pytest.fixture
 def deposit_contract_address():
     return SERENITY_CONFIG.DEPOSIT_CONTRACT_ADDRESS

tests/beacon/state_machines/conftest.py

@@ -16,6 +16,7 @@ def config(
         bls_withdrawal_prefix_byte,
         max_casper_votes,
         latest_block_roots_length,
+        latest_randao_mixes_length,
         deposit_contract_address,
         deposit_contract_tree_depth,
         min_deposit,
@@ -49,6 +50,7 @@ def config(
         BLS_WITHDRAWAL_PREFIX_BYTE=bls_withdrawal_prefix_byte,
         MAX_CASPER_VOTES=max_casper_votes,
         LATEST_BLOCK_ROOTS_LENGTH=latest_block_roots_length,
+        LATEST_RANDAO_MIXES_LENGTH=latest_randao_mixes_length,
         DEPOSIT_CONTRACT_ADDRESS=deposit_contract_address,
         DEPOSIT_CONTRACT_TREE_DEPTH=deposit_contract_tree_depth,
         MIN_DEPOSIT=min_deposit,

tests/beacon/types/test_states.py

@@ -34,8 +34,8 @@ def empty_beacon_state():
         validator_registry_latest_change_slot=10,
         validator_registry_exit_count=10,
         validator_registry_delta_chain_tip=b'\x55' * 32,
-        randao_mix=b'\x55' * 32,
-        next_seed=b'\x55' * 32,
+        latest_randao_mixes=(),
+        latest_vdf_outputs=(),
         shard_committees_at_slots=(),
         persistent_committees=(),
         persistent_committee_reassignments=(),