EIP-6466: SSZ Receipts

Migration of RLP receipts to SSZ

Metadata

Status: DraftStandards Track: CoreCreated: 2023-02-08

Authors

Etan Kissling (@etan-status), Vitalik Buterin (@vbuterin)

Requires

EIP-658, EIP-6404

Links

GitHub page Discussion on Ethereum Magicians

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:

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.
Unnecessary statefulness: EIP-658 replaced the intermediate post-state root from receipts with a boolean status code. However, cumulativeGasUsed is similarly stateful, unnecessarily complicating efforts to execute transactions in parallel. Furthermore, multiple receipts are required to verify the effective gas used by an individual transaction.
Incomplete data: JSON-RPC provides contractAddress in the receipt for a transaction creating a new contract, but the receipt does not contain the required information to verify it. Workarounds that rely on also fetching the transaction data may not be future-proof.

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.

Name	Value
`MAX_TRANSACTIONS_PER_PAYLOAD`	`uint64(2**20)` (= 1,048,576)
`BYTES_PER_LOGS_BLOOM`	`uint64(2**8)` (= 256)
`SSZ_TX_TYPE`	`0x04`

Name	SSZ equivalent
`Root`	`Bytes32`

`Receipt` container

All receipts are represented as a single, normalized SSZ container. The definition uses the StableContainer[N] SSZ type and Optional[T] as defined in EIP-7495.

Name	Value	Description
`MAX_TOPICS_PER_LOG`	`4`	`LOG0` through `LOG4` opcodes allow 0-4 topics per log
`MAX_LOG_DATA_SIZE`	`uint64(2**24)` (= 16,777,216)	Maximum `data` byte length for a log
`MAX_LOGS_PER_RECEIPT`	`uint64(2**21)` (= 2,097,152)	Maximum number of entries within `logs`
`MAX_RECEIPT_FIELDS`	`uint64(2**5)` (= 32)	Maximum number of fields to which `Receipt` can ever grow in the future

Receipt merkleization

Execution block header changes

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

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.

Networking

When exchanging SSZ receipts via the Ethereum Wire Protocol, the following EIP-2718 compatible envelope is used:

Receipt: SSZ_TX_TYPE || snappyFramed(ssz(Receipt))

Objects are encoded using SSZ and compressed using the Snappy framing format, matching the encoding of consensus objects as defined in the consensus networking specification. As part of the encoding, the uncompressed object length is emitted; the RECOMMENDED limit to enforce per object is MAX_CHUNK_SIZE bytes.

Rationale

SSZ merkleization allows verification of individual chunks of receipt data, reducing complexity for client applications and smart contracts. Additionally, SSZ StableContainer enables unification of the receipt format across all EIP-2718 transaction types and provides forward compatibility.

Backwards Compatibility

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

Applications using verified cumulativeGasUsed values have to compute the value from prior receipts.

Security Considerations

None