Part 3: Annotated Specification
The following are the various protocol messages that can be transmitted in a block` on the beacon chain.
For most of these, the proposer is rewarded either explicitly or implicitly for including the object in a block.
The proposer receives explicit in-protocol rewards for including the following in blocks:
Deposit objects in blocks is only implicitly rewarded, in that, if there are pending deposits that the block proposer does not include then the block is invalid, so the proposer receives no reward.
There is no direct reward for including
VoluntaryExit objects. However, for each validator exited, rewards for the remaining validators increase very slightly, so it's still beneficial for proposers not to ignore
class ProposerSlashing(Container): signed_header_1: SignedBeaconBlockHeader signed_header_2: SignedBeaconBlockHeader
ProposerSlashings may be included in blocks to prove that a validator has broken the rules and ought to be slashed. Proposers receive a reward for correctly submitting these.
In this case, the rule is that a validator may not propose two different blocks at the same height, and the payload is the signed headers of the two blocks that evidence the crime. The signatures on the
SignedBeaconBlockHeaders are checked to verify that they were both signed by the accused validator.
class AttesterSlashing(Container): attestation_1: IndexedAttestation attestation_2: IndexedAttestation
AttesterSlashings may be included in blocks to prove that one or more validators in a committee has broken the rules and ought to be slashed. Proposers receive a reward for correctly submitting these.
The contents of the
IndexedAttestations are checked against the attester slashing conditions in
is_slashable_attestation_data(). If there is a violation, then any validator that attested to both
attestation_2 is slashed, see
AttesterSlashings can be very large since they could in principle list the indices of all the validators in a committee. However, in contrast to proposer slashings, many validators can be slashed as a result of a single report.
class Attestation(Container): aggregation_bits: Bitlist[MAX_VALIDATORS_PER_COMMITTEE] data: AttestationData signature: BLSSignature
This is the form in which attestations make their way around the network. It is designed to be easily aggregatable:
Attestations containing identical
AttestationData can be combined into a single attestation by aggregating the signatures.
Attestations contain the same information as
IndexedAttestations, but use knowledge of the validator committees at slots to compress the list of attesting validators down to a bitlist. Thus,
Attestations are at least 5 times smaller than
IndexedAttestations, and up to 35 times smaller (with 128 or 2048 validators per committee, respectively).
When a validator first broadcasts its attestation to the network, the
aggregation_bits list will contain only a single bit set, and calling
get_attesting_indices() on it will return a list containing only a single entry, the validator's own index.
class Deposit(Container): proof: Vector[Bytes32, DEPOSIT_CONTRACT_TREE_DEPTH + 1] # Merkle path to deposit root data: DepositData
This container is used to include deposit data from prospective validators in beacon blocks so that they can be processed into beacon state.
proof is a Merkle proof constructed by the block proposer that the
DepositData corresponds to the previously agreed deposit root of the Eth1 contract's deposit tree. It is verified in
class VoluntaryExit(Container): epoch: Epoch # Earliest epoch when voluntary exit can be processed validator_index: ValidatorIndex
Voluntary exit messages are how a validator signals that it wants to cease being a validator. Blocks containing
VoluntaryExit data for an epoch later than the current epoch are invalid, so nodes should buffer or ignore any future-dated exits they see.
VoluntaryExit objects are never used naked; they are always wrapped up into a
class SyncAggregate(Container): sync_committee_bits: Bitvector[SYNC_COMMITTEE_SIZE] sync_committee_signature: BLSSignature
The prevailing sync committee is stored in the beacon state, so the
SyncAggregates included in blocks need only use a bit vector to indicate which committee members signed off on the message.
sync_committee_signature is the aggregate signature of all the validators referenced in the bit vector over the block root of the previous slot.
SyncAggregates are handled by
class BLSToExecutionChange(Container): validator_index: ValidatorIndex from_bls_pubkey: BLSPubkey to_execution_address: ExecutionAddress
The Capella upgrade gives validators that have old style BLS withdrawal credentials a one-time opportunity to update them to Eth1 withdrawal credentials.
To make this change, a staker needs to broadcast a signed message containing this information via a consensus node. It will eventually be included in a block at which point nodes will verify it and update their validator registries. The
from_bls_pubkey is verified against the validator's existing withdrawal credential, and the message's signature is verified against the