Part 3: Annotated Specification

Initialise State

Introduction

TODO: rework and synthesis - this text is from the original Genesis.

Before the Ethereum beacon chain genesis has been triggered, and for every Ethereum proof-of-work block, let candidate_state = initialize_beacon_state_from_eth1(eth1_block_hash, eth1_timestamp, deposits) where:

eth1_block_hash is the hash of the Ethereum proof-of-work block
eth1_timestamp is the Unix timestamp corresponding to eth1_block_hash
deposits is the sequence of all deposits, ordered chronologically, up to (and including) the block with hash eth1_block_hash

Proof-of-work blocks must only be considered once they are at least SECONDS_PER_ETH1_BLOCK * ETH1_FOLLOW_DISTANCE seconds old (i.e. eth1_timestamp + SECONDS_PER_ETH1_BLOCK * ETH1_FOLLOW_DISTANCE <= current_unix_time). Due to this constraint, if GENESIS_DELAY < SECONDS_PER_ETH1_BLOCK * ETH1_FOLLOW_DISTANCE, then the genesis_time can happen before the time/state is first known. Values should be configured to avoid this case.

Initialisation

Aka genesis.

This helper function is only for initializing the state for pure Capella testnets and tests.

def initialize_beacon_state_from_eth1(eth1_block_hash: Hash32,
                                      eth1_timestamp: uint64,
                                      deposits: Sequence[Deposit],
                                      execution_payload_header: ExecutionPayloadHeader=ExecutionPayloadHeader()
                                      ) -> BeaconState:
    fork = Fork(
        previous_version=CAPELLA_FORK_VERSION,  # [Modified in Capella] for testing only
        current_version=CAPELLA_FORK_VERSION,  # [Modified in Capella]
        epoch=GENESIS_EPOCH,
    )
    state = BeaconState(
        genesis_time=eth1_timestamp + GENESIS_DELAY,
        fork=fork,
        eth1_data=Eth1Data(block_hash=eth1_block_hash, deposit_count=uint64(len(deposits))),
        latest_block_header=BeaconBlockHeader(body_root=hash_tree_root(BeaconBlockBody())),
        randao_mixes=[eth1_block_hash] * EPOCHS_PER_HISTORICAL_VECTOR,  # Seed RANDAO with Eth1 entropy
    )

    # Process deposits
    leaves = list(map(lambda deposit: deposit.data, deposits))
    for index, deposit in enumerate(deposits):
        deposit_data_list = List[DepositData, 2**DEPOSIT_CONTRACT_TREE_DEPTH](*leaves[:index + 1])
        state.eth1_data.deposit_root = hash_tree_root(deposit_data_list)
        process_deposit(state, deposit)

    # Process activations
    for index, validator in enumerate(state.validators):
        balance = state.balances[index]
        validator.effective_balance = min(balance - balance % EFFECTIVE_BALANCE_INCREMENT, MAX_EFFECTIVE_BALANCE)
        if validator.effective_balance == MAX_EFFECTIVE_BALANCE:
            validator.activation_eligibility_epoch = GENESIS_EPOCH
            validator.activation_epoch = GENESIS_EPOCH

    # Set genesis validators root for domain separation and chain versioning
    state.genesis_validators_root = hash_tree_root(state.validators)

    # Fill in sync committees
    # Note: A duplicate committee is assigned for the current and next committee at genesis
    state.current_sync_committee = get_next_sync_committee(state)
    state.next_sync_committee = get_next_sync_committee(state)

    # Initialize the execution payload header
    state.latest_execution_payload_header = execution_payload_header

    return state

Each state fields start with its default SSZ value unless a value is explicitly provided. So, for example, state.next_withdrawal_index will be initialised to zero, and state.historical_summaries to an empty list.

Genesis state

Let genesis_state = candidate_state whenever is_valid_genesis_state(candidate_state) is True for the first time.

def is_valid_genesis_state(state: BeaconState) -> bool:
    if state.genesis_time < MIN_GENESIS_TIME:
        return False
    if len(get_active_validator_indices(state, GENESIS_EPOCH)) < MIN_GENESIS_ACTIVE_VALIDATOR_COUNT:
        return False
    return True

TODO

Genesis block

Let genesis_block = BeaconBlock(state_root=hash_tree_root(genesis_state)).

TODO