EIP712 salt is always keccak256 hashed

[TimDaub]

Version
main branch latest today

Platform
all

Description

• I've been working on a software project where we use both JS and Rust to generate valid EIP712 signatures and we're not using a contract to verify the signature but our own nodes (similar to how Farcaster does it).
• Inspired by them, I've been using the "salt" domain separator: https://github.com/farcasterxyz/hub-monorepo/blob/59920f9716838a19749f41c4f3c7f9ac979cac07/packages/utils/src/crypto/eip712.ts#L11
• But it seems that ethers-rs (in contrast to ethers-js) is always hashing the salt value using keccak256
  • JS: https://github.com/ethers-io/ethers.js/blob/v5.2/packages/hash/src.ts/typed-data.ts#L70
  • Rust:

    ethers-rs/ethers-core/src/types/transaction/eip712.rs

    Line 383 in 64b7f1e

    let salt = keccak256(lit_str.value());

  • Rust2:

    ethers-rs/ethers-core/ethers-derive-eip712/src/lib.rs

    Line 18 in 404422e

    //! that is hashed using keccak256 and stored as bytes.

• And so now this isn't ideal for me. Because I'd rather just input a 32 bytes long sequence instead of having implicit hashing.
• So I've been thinking of just proposing to remove the line in the Rust implementation, but then that'd break the interface for existing users
• So what's an elegant solution for passing in 32 bytes that aren't later hashed?

[prestwich]

cc @DaniPopes, who has been touching this code recently. The best non-breaking way is probably to add a raw_salt that gets parsed as a H256 and is mutually exclusive with salt?