Elected block proposer has not been slashed

Abstract

Introduces a modification to the consensus layer specification which ensures that slashed validator cannot be elected as block proposer.

Motivation

A block proposed by a slashed validator is rejected by the corresponding validity check in the phase0/process_block_header function as defined in the consensus layer specification.

At the same time the definition of the phase0/compute_proposer_index allows for a slashed validator to be elected as a proposer. This contradiction effectively leads to a missed proposal if it is supposed to be made by a slashed validator.

The impact of the proposed fix in the case of a single slashing on Ethereum Mainnet is negligible but it becomes significant in the case of correlated slashings. For instance, a correlated slashing of 1/10th of a validator set can lead to 1/10th of missed proposals in a number of epochs after the slashing.

Specification

Specification of the proposed change can be found in /_features/eip6988/beacon-chain.md.

Rationale

Modifying get_beacon_proposer_index

This function is modified to read a proposer index from a beacon state if a slot of a latest block header is the same as the state.slot.

This modification is done to make the function return correct proposer index in the case when the proposer of a given block is being slashed during processing of the block.

Backwards Compatibility

This fix changes proposer election mechanism in a backwards incompatible way and requires a hard fork to be deployed.

Test Cases

The following test cases were added to cover this change:

• test_slashed_proposer_rewarded_for_sync_aggregate_inclusion
• test_slashed_proposer_rewarded_for_attestation_inclusion
• test_slashed_validator_not_elected_for_proposal
• test_slashed_validator_elected_for_proposal

Reference Implementation

Reference implementation is in the same place as Specification.

Security Considerations

There are no observed security issues introduced by the proposed change.

Copyright

Copyright and related rights waived via CC0.