EIP-6466: SSZ receipts

Migration of RLP receipts to SSZ

Abstract

This EIP defines a migration process of EIP-2718 Recursive-Length Prefix (RLP) receipts to Simple Serialize (SSZ)

Motivation

RLP receipts have a number of shortcomings:

1. Limited proving support: Due to receipt data being linearly hashed as part of the receipts_root Merkle-Patricia Trie (MPT), it is not possible to efficiently proof individual parts of receipts, such as logs. Requiring the full receipt data to be present can be prohibitive for smart contract based applications such as L2 fraud proofs or client applications verifying log data.

2. Incomplete data: JSON-RPC provides from, gasUsed, and contractAddress fields for receipts, but the on-chain receipt does not contain the required information to verify them.

This EIP defines a universal receipt format based on SSZ to address these concerns.

Specification

The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “NOT RECOMMENDED”, “MAY”, and “OPTIONAL” in this document are to be interpreted as described in RFC 2119 and RFC 8174.

Existing definitions

Definitions from existing specifications that are used throughout this document are replicated here for reference.

Logs

Logs are represented as an SSZ Container.

class Log(Container):
    address: ExecutionAddress
    topics: List[Bytes32, MAX_TOPICS_PER_LOG]
    data: ProgressiveByteList

Receipts

New receipts use a normalized SSZ representation.

class Receipt(CompatibleUnion({
    0x01: BasicReceipt,
    0x02: CreateReceipt,
    0x03: SetCodeReceipt,
})):
    pass

Basic receipts

This receipt is emitted for these transactions:

• RlpLegacyReplayableBasicTransaction
• RlpLegacyBasicTransaction
• RlpAccessListBasicTransaction
• RlpBasicTransaction
• RlpBlobTransaction

class BasicReceipt(
    ProgressiveContainer(active_fields=[1, 1, 0, 1, 1])
):
    from_: ExecutionAddress
    gas_used: GasAmount
    logs: ProgressiveList[Log]
    status: boolean

Create receipts

This receipt is emitted for these transactions:

• RlpLegacyReplayableCreateTransaction
• RlpLegacyCreateTransaction
• RlpAccessListCreateTransaction
• RlpCreateTransaction

class CreateReceipt(
    ProgressiveContainer(active_fields=[1, 1, 1, 1, 1])
):
    from_: ExecutionAddress
    gas_used: GasAmount
    contract_address: ExecutionAddress
    logs: ProgressiveList[Log]
    status: boolean

EIP-7702 set code receipts

This receipt is emitted for these transactions:

• RlpSetCodeTransaction

class SetCodeReceipt(
    ProgressiveContainer(active_fields=[1, 1, 0, 1, 1, 1])
):
    from_: ExecutionAddress
    gas_used: GasAmount
    logs: ProgressiveList[Log]
    status: boolean
    authorities: ProgressiveList[ExecutionAddress]

Receipt construction

Receipts are constructed as follows.

The logs_bloom, intermediate state root (Homestead scheme), and cumulative_gas_used (pre EIP-8116) fields are not present in SSZ receipts.

Execution block header changes

The execution block header’s receipts-root is transitioned from MPT to SSZ.

receipts = ProgressiveList[Receipt](
    receipt_0, receipt_1, receipt_2, ...)

block_header.receipts_root = receipts.hash_tree_root()

JSON-RPC API

Transaction receipt objects in the context of the JSON-RPC API are extended to include:

• authorities: Array of DATA|null - Array of DATA entries each containing 20 Bytes, corresponding to the receipt’s authorities field

The logsBloom field is no longer returned for new receipts. It continues to be returned for historical receipts conforming to earlier schemes.

from, gasUsed, and contractAddress are already provided via JSON-RPC and are left unchanged. For BasicReceipt and SetCodeReceipt, contractAddress will be null as these receipt types do not contain the contract_address field. logIndex indicates the log index position in the individual receipt (rather than the entire block), as defined in EIP-8116.

Consensus ExecutionPayload changes

When building a consensus ExecutionPayload, the receipts_root is now based on the Receipt type, changing the type of receipts_root from an MPT Hash32 to an SSZ Root.

class ExecutionPayload(...):
    ...
    receipts_root: Root
    ...

class ExecutionPayloadHeader(...):
    ...
    receipts_root: Root
    ...

payload_header.receipts_root = payload.receipts_root

Rationale

Forward compatibility

All receipts share the same Merkle tree shape with a stable generalized index (gindex) assigned to each field. Future transaction features can introduce additional receipt fields or drop existing fields without breaking verifiers.

Verifier improvements

Committing to from, contract_address and authorities in the receipt allows efficient verification without the expensive ecrecover mechanism. This allows future EIPs to change how these addresses are computed without breaking verifiers, e.g., when future signature schemes are introduced.

Execution client improvements

Execution Layer implementations no longer need access to the transaction and additional indices when serving receipts based on SSZ.

Backwards Compatibility

Applications that rely on the replaced MPT receipts_root in the block header require migration to the SSZ receipts_root.

RLP and SSZ receipts may clash when encoded. It is essential to use only a single format within one channel. When requesting receipts by hash over the network, the block header corresponding to the containing receipts root can be consulted to identify the underlying fork.

Security Considerations

None

Copyright

Copyright and related rights waived via CC0.

Citation

Please cite this document as:

Etan Kissling (@etan-status), Gajinder Singh (@g11tech), Vitalik Buterin (@vbuterin), "EIP-6466: SSZ receipts [DRAFT]," Ethereum Improvement Proposals, no. 6466, February 2023. [Online serial]. Available: https://eips.ethereum.org/EIPS/eip-6466.