EIP-7804: Withdrawal Credential Update Request

Allow validators to update their withdrawal credentials via execution requests

Metadata

Status: DraftStandards Track: CoreCreated: 2024-10-31

Authors

Lucas Saldanha (@lucassaldanha), Mikhail Kalinin (@mkalinin)

Links

GitHub page Discussion on Ethereum Magicians

Abstract

This proposal defines a mechanism to allow validators to update their withdrawal credentials using a new execution request type (0x03). The request allows for changing the execution address and the withdrawal credential prefix (0x01 or 0x02).

Motivation

When the ability to update a validator BLS withdrawal credentials to execution address was introduced in Capella, one of the most common questions was about allowing the withdrawal credential to be changed in the future. Either for security (e.g. credential rotation) or to allow for alternative ways of handling withdrawals (e.g. having a contract address as credentials). The main reason for not adding this options was because implementing this communication channel between the Execution Layer and the Consensus Layer is complex (based on the experience with the Eth1 bridge).

In Electra, the protocol was upgraded with Execution Requests (deposits, withdrawals and consolidations), and a mechanism for general purpose execution requests EIP-7685, decreasing the complexity of adding a new request from execution to consensus layer.

The introduction of execution requests that are created on the execution layer, opened up possibilities on how validators can be managed. Execution request can be created via smart contracts, allowing for decentralized and on-chain mechanisms to be explored. This also means validators will be able to move between execution and compounding withdrawal credentials (follwoing the correct churn on the total staked amount).

For an execution request to be authorized in the consensus layer, the withdrawal credential of the validator must be the same of the msg.caller when processing the transaction on the EVM. So the validator's withdrawal credential must be the same address of the smart contract creating the request (not the credential of the transaction sender), or the contract needs to use DELEGATECALL to ensure the caller address matches the address in the validator's withdrawal credential. Validators that already have a contract address as their withdrawal credentials should be able to update their contracts to meet this demand (assuming they have an updatable contract).

There problems for existing validators that have their withdrawal credentials set to an EOA account is they will never be able to use use smart contracts for creating execution requests, because the current design does not allow for these credentials to ever be changed.

Allowing for validators to update their withdrawal credentials mean they can opt-in and out of different schemes and strategies on managing their validators, favouring experimentation and innovation. Today, the only alternative to this is exitting the validator and creating a new validator with different withdrawal credentials.

Specification

Constants

Name	Value	Comment
`FORK_TIMESTAMP`	TBD	Mainnet

Configuration

Name	Value	Comment
`WITHDRAWAL_CREDENTIALS_UPDATE_REQUEST_PREDEPLOY_ADDRESS`	`0x09Fc772D0857550724b07B850a4323f39112aAaA`	Where to call and store relevant details about the withdrawal credentials update mechanism
`WITHDRAWAL_CREDENTIALS_UPDATE_REQUEST_TYPE`	`0x03`	The EIP-7685 type prefix for withdrawal credential update request
`SYSTEM_ADDRESS`	`0xfffffffffffffffffffffffffffffffffffffffe`	Address used to invoke system operation on contract
`EXCESS_WITHDRAWAL_CREDENTIALS_UPDATE_REQUESTS_STORAGE_SLOT`	0
`WITHDRAWAL_CREDENTIALS_UPDATE_REQUEST_COUNT_STORAGE_SLOT`	1
`WITHDRAWAL_CREDENTIALS_UPDATE_REQUEST_QUEUE_HEAD_STORAGE_SLOT`	2	Pointer to head of the withdrawal credential update request message queue
`WITHDRAWAL_CREDENTIALS_UPDATE_REQUEST_QUEUE_TAIL_STORAGE_SLOT`	3	Pointer to the tail of the withdrawal credential update request message queue
`WITHDRAWAL_CREDENTIALS_UPDATE_REQUEST_QUEUE_STORAGE_OFFSET`	4	The start memory slot of the in-state withdrawal credential update request message queue
`MAX_WITHDRAWAL_CREDENTIALS_UPDATE_REQUESTS_PER_BLOCK`	4	Maximum number of withdrawal credential update requests that can be dequeued into a block
`TARGET_WITHDRAWAL_CREDENTIALS_UPDATE_REQUESTS_PER_BLOCK`	1
`MIN_WITHDRAWAL_CREDENTIALS_UPDATE_REQUEST_FEE`	1
`WITHDRAWAL_CREDENTIALS_UPDATE_REQUEST_FEE_UPDATE_FRACTION`	17
`EXCESS_INHIBITOR`	`2**256-1`	Excess value used to compute the fee before the first system call

Execution Layer

FORK_BLOCK -- the first block in a blockchain with the timestamp greater or equal to FORK_TIMESTAMP.

Withdrawal Credentials Update request operation

The new withdrawal credential update request operation is an EIP-7685 request with type 0x03 and consists of the following fields:

pubkey: Bytes48
old_address: Bytes20
new_address: Bytes20

The EIP-7685 encoding of a withdrawal credential update request is computed as follows.

Withdrawal Credentials Update Request Contract

The contract is similar to other execution requests contracts for Deposits, Withdrawals and Consolidation. The contract has three different code paths, which can be summarized at a high level as follows:

Add request - requires a 68 byte input, the validator's public key concatenated with the new address for withdrawal credentials.
Excess requests getter - if the input length is zero, return the current excess requests count.
System process - if called by system address, pop off the withdrawal credential update requests for the current block from the queue.

Block processing

At the end of processing any execution block where block.timestamp >= FORK_TIMESTAMP (i.e. after processing all transactions and after performing the block body requests validations) client software MUST include a call the contract as SYSTEM_ADDRESS and empty input data to trigger the system subroutine execute. The resopnse should be treated as a new request type (0x03) according to EIP-7685.

Block Validation

EL must check that the commitment hash in the execution block header matches the hash of the list of execution requests the CL sends when validating the execution block (including any requests of the the new defined type 0x03).

Consensus Layer

Summary of changes:

New container WithdrawalCredentialUpdateRequest
New method in Block Processing: process_withdrawal_credential_update_request
New Beacon State mutator method: update_withdrawal_credentials

Rationale

Backwards Compatibility

Test Cases

Security Considerations

Ownership is defined based on control of the withdrawal credential account, either as a private key (for EOA accounts) or controlling the smart contract at the address set as withdrawal credential. Therefore allowing an update should not bring any security implications.

Futher discussion needed.