# ERC-7964 pull request proposes a breaking change to signatures

Canonical: https://forkbrief.com/news/ad8ec443-9491-4a58-b05c-213463abae7f
Published: 2026-10-24T01:07:53.026Z
Publisher: Fork Brief

An open proposal would remove a field byte and change how verifiers build the main signing domain.

ERC-7964 author Ernesto García opened a [pull request](https://github.com/ethereum/ERCs/pull/2112) on October 23 proposing a breaking change to crosschain signatures. The revision would remove a domain-fields byte from the signature header and make the verifier determine which fields belong in the main signing domain.

[ERC-7964](https://eips.ethereum.org/EIPS/eip-7964) describes an EIP-712 message covering operations on multiple chains. Each chain receives an array of operation hashes and the full message data relevant to its own operation. The standard remains Draft; it was originally created in June 2025.

## Domain fields would come from the verifier

Under the revision, a verifier would declare `chainFields`, a bitmap describing which domain fields its chain-specific structures already bind. It would derive the remaining main-domain fields using `applicationFields & ~chainFields`, with the application's fields obtained through `eip712Domain()`.

García's [discussion update](https://ethereum-magicians.org/t/erc-7964-cross-chain-signatures-for-account-abstraction/24452/11) gives a concrete example: application fields `0x0f` and chain fields `0x0c` produce `0x03`, leaving name and version in the main domain. The chain bitmap must include the `chainId` bit.

## The header would still occupy 32 bytes

The proposed header contains a ten-byte magic value, a two-byte operation index and a 20-byte application address. The currently published draft instead uses a nine-byte magic value and a separate one-byte fields bitmap alongside that index and address.

The outer signature envelope would remain an ABI-encoded tuple containing the header, operation hashes and signature. Its reference verification function would gain a `chainFields` argument. The author says the new detector would no longer recognize the old encoding.

The pull request remains open and unmerged. It proposes a specification change; it does not establish wallet adoption or deployment.

## Sources

- [ERC-7964 author update: main domain fields derived by verifier](https://ethereum-magicians.org/t/erc-7964-cross-chain-signatures-for-account-abstraction/24452/11) — Ethereum Magicians / ernestognw
- [ERC-7964: Crosschain EIP-712 Signatures \[DRAFT\]](https://eips.ethereum.org/EIPS/eip-7964) — Ethereum Improvement Proposals
- [Update ERC-7964: Derive main domain fields on the verifier](https://github.com/ethereum/ERCs/pull/2112) — ethereum/ERCs

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