DCIPs/eip-6110.md at 58b766a9239b34a0ac2934744f6d5124a1ba7c54

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eip	title	description	author	discussions-to	status	type	category	created
6110	Supply validator deposits on chain	Provides validator deposits as a list of deposit operations added to the Execution Layer block	Mikhail Kalinin (@mkalinin), Danny Ryan (@djrtwo)	https://ethereum-magicians.org/t/eip-6110-supply-validator-deposits-on-chain/12072	Draft	Standards Track	Core	2022-12-09

Abstract

Appends validator deposits to the Execution Layer block structure. This shifts responsibility of deposit inclusion and validation to the Execution Layer and removes the need for deposit (or eth1data) voting from the Consensus Layer.

Validator deposits list supplied in a block is obtained by parsing deposit contract log events emitted by each deposit transaction included in a given block.

Motivation

Validator deposits are a core component of the proof-of-stake consensus mechanism. This EIP allows for an in-protocol mechanism of deposit processing on the Consensus Layer and eliminates the proposer voting mechanism utilized currently. This proposed mechanism relaxes safety assumptions and reduces complexity of client software design, contributing to the security of the deposits flow. It also improves validator UX.

Advantages of in-protocol deposit processing consist of but are not limit to the following:

Significant increase of deposits security by supplanting proposer voting. With the proposed in-protocol mechanism, an honest online node can't be convinced to process fake deposits even when more than 2/3 portion of stake is adversarial.
Decrease of delay between submitting deposit transaction on Execution Layer and its processing on Consensus Layer. That is, ~13 minutes with in-protocol deposit processing compared to ~12 hours with the existing mechanism.
Eliminate beacon block proposal dependency on JSON-RPC API data polling that suffers from failures caused by inconsistencies between JSON-RPC API implementations and dependency of API calls processing on the inner state (e.g. syncing) of client software.
Eliminate requirement to maintain and distribute deposit contract snapshots (EIP-4881).
Reduction of design and engineering complexity of Consensus Layer client software on a component that has proven to be brittle.

Specification

Constants

Name	Value	Comment
`FORK_TIMESTAMP`	TBD	Mainnet

Configuration

Name	Value	Comment
`DEPOSIT_CONTRACT_ADDRESS`	`0x00000000219ab540356cbb839cbe05303d7705fa`	Mainnet

DEPOSIT_CONTRACT_ADDRESS parameter MUST be included into client software binary distribution.

Definitions

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

Deposit

The structure denoting the new deposit operation consists of the following fields:

pubkey: Bytes48
withdrawal_credentials: Bytes32
amount: uint64
signature: Bytes96
index: uint64

RLP encoding of deposit structure MUST be computed in the following way:

rlp_encoded_deposit = RLP([
    RLP(pubkey),
    RLP(withdrawal_credentials),
    RLP(amount),
    RLP(signature),
    RLP(index)
])

Block structure

Beginning with the FORK_BLOCK, the block body MUST be appended with a list of deposit operations. RLP encoding of an extended block body structure MUST be computed as follows:

block_body_rlp = RLP([
    rlp_encoded_field_0,
    ...,
    # Latest block body field before `deposits`
    rlp_encoded_field_n,
    
    RLP([rlp_encoded_deposit_0, ..., rlp_encoded_deposit_k])
])

Beginning with the FORK_BLOCK, the block header MUST be appended with the new deposits_root field. The value of this field is the trie root committing to the list of deposits in the block body. deposits_root field value MUST be computed as follows:

def compute_trie_root_from_indexed_data(data):
    trie = Trie.from([(i, obj) for i, obj in enumerate(data)])
    return trie.root

block.header.deposits_root = compute_trie_root_from_indexed_data(block.body.deposits)

Block validity

Beginning with the FORK_BLOCK, client software MUST extend block validity rule set with the following conditions:

Value of deposits_root block header field equals to the trie root committing to the list of deposit operations contained in the block. To illustrate:

def compute_trie_root_from_indexed_data(data):
    trie = Trie.from([(i, obj) for i, obj in enumerate(data)])
    return trie.root

assert block.header.deposits_root == compute_trie_root_from_indexed_data(block.body.deposits)

The list of deposit operations contained in the block MUST be equivalent to the list of log events emitted by each deposit transaction of the given block, respecting the order of transaction inclusion. To illustrate:

def parse_deposit_data(deposit_event_data): bytes[]
  """
  Parses Deposit operation from DepositContract.DepositEvent data
  """
  pass

def little_endian_to_uint64(data: bytes): uint64
    return uint64(int.from_bytes(data, 'little'))

class Deposit(object):
    pubkey: Bytes48
    withdrawal_credentials: Bytes32
    amount: uint64
    signature: Bytes96
    index: uint64

def event_data_to_deposit(deposit_event_data): Deposit
  deposit_data = parse_deposit_data(deposit_event_data)
  return Deposit(
    pubkey=Bytes48(deposit_data[0]),
    withdrawal_credentials=Bytes32(deposit_data[1]),
    amount=little_endian_to_uint64(deposit_data[2]),
    signature=Bytes96(deposit_data[3]),
    index=little_endian_to_uint64(deposit_data[4])
  )

# Obtain receipts from block execution result
receipts = block.execution_result.receipts

# Retrieve all deposits made in the block
expected_deposits = []
for receipt in receipts:
    for log in receipt.logs:
        if log.address == DEPOSIT_CONTRACT_ADDRESS:
            deposit = event_data_to_deposit(log.data)
            expected_deposits.append(deposit)

# Compare retrieved deposits to the list in the block body
assert block.body.deposits == expected_deposits

A block that does not satisfy the above conditions MUST be deemed invalid.

Rationale

`index` field

The index field may appear unnecessary but it is important information for deposit processing flow on the Consensus Layer.

Not limiting the size of deposit operations list

The list is unbounded because of negligible data complexity and absence of potential DoS vectors. See Security Considerations for more details.

Filtering events only by `DEPOSIT_CONTRACT_ADDRESS`

Deposit contract does not emit any events except for DepositEvent, thus additional filtering is unnecessary.

Backwards Compatibility

This EIP introduces backwards incompatible changes to the block structure and block validation rule set. But neither of these changes break anything related to user activity and experience.

Security Considerations

Data complexity

At the time of writing this document, the total number of submitted deposits is 478,402 which is 88MB of deposit data. Assuming frequency of deposit transactions remains the same, historic chain data complexity induced by this EIP can be estimated as 50MB per year which is negligible in comparison to other historic data.

After the beacon chain launch in December 2020, the biggest observed spike in a number of submitted deposits was on March 15, 2022. More than 6000 deposit transactions were submitted during 24 hours which on average is less than 1 deposit, or 192 bytes of data, per block.

Considering the above, we conclude that data complexity introduced by this proposal is negligible.

DoS vectors

With 1 ETH as a minimum deposit amount, the lowest cost of a byte of deposit data is 1 ETH/192 ~ 5,208,333 Gwei. This is several orders of magnitude higher than the cost of a byte of transaction's calldata, thus adding deposit operations to a block does not increase Execution Layer DoS attack surface.

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