EIP-6466: SSZ receipts

Abstract

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

Motivation

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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. 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.

3. 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.

4. Inefficient logs bloom: The logs bloom mechanism is inefficient due to its high false positive rate. It does not find enough practical use to warrant its high storage requirement, and should be removed.

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

Specification

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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)
MAX_AUTHORIZATION_LIST_SIZE	uint64(2**16) (= 65,536)
SSZ_TX_TYPE	0x1f

Name	SSZ equivalent
Root	Bytes32
ExecutionAddress	Bytes20
GasAmount	uint64

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 construction

Receipts are constructed as follows.

Field	Description
from	The transaction sender's address
gas_used	How much gas this individual transaction used. Replaces cumulative_gas_used
contract_address	For transactions deploying a contract, the new contract address
logs	Logs emitted during transaction execution
status	EIP-658 transaction status code
authorities	For transactions with an authorization list, the list of EIP-7702 authority addresses. Non-successful authorizations are represented with an all-zero address

The logs_bloom and intermediate state root (Homestead scheme) are not present in SSZ receipts.

Execution block header changes

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

JSON-RPC API

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

• authorities: Array of DATA|null - 0 through MAX_AUTHORIZATION_LIST_SIZE 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.

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

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Switching to a single, unified and forward compatible receipt format within execution blocks reduces implementation complexity for client applications and smart contracts. Individual chunks of receipt data can now be verified, simplifying implementation of bridges.

Light clients can now efficiently verify a receipt's from, gas_used, and authorities, which previously required obtaining the corresponding transaction data and additional receipts. Execution layer implementations no longer have to compute signer addresses using the expensive ecrecover mechanism when backfilling / serving historical receipt data.

Removal of logs_bloom reduces storage cost for receipts by 259 bytes per receipt.

Backwards Compatibility

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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.

Applications relying on the logsBloom will have to swap to an out-of-protocol mechanism for filtering logs, or fall back to processing the complete set of receipts. As the logsBloom mechanism was prohibitively inefficient for light clients, its removal is unlikely to have a significant impact.

Security Considerations

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None

Copyright

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Copyright and related rights waived via CC0.