Add ERC: Composite EIP-712 Signatures

[sola92]

This EIP provides a scheme for signing multiple typed-data messages with a single signature by encoding them into a Merkle tree. Allowing individual messages to be verified without requiring full knowledge of the others.

[eip-review-bot]

✅ All reviewers have approved.

[xinbenlv]

Dear sola92,

Thank you for proposing ERC-7920. The composite signature approach via Merkle trees addresses a critical UX gap in multi-message workflows. Below is concise technical feedback to strengthen the proposal:

Critical Revisions

1. Security Fix (Line 100):

   // Replace encodePacked with encode to prevent collisions
   - abi.encodePacked("\x19\x01", ...)  
   + abi.encode("\x19\x01", ...)  

2. Merkle Tree Specs (Lines 45-47):

   • Add explicit requirements for:
     • Single-message roots (root = leaf)
     • Leaf ordering (lexicographical sort)
     • Zero-padding for unbalanced trees
   • Reference RFC 6962 for tree construction.

3. Wallet Requirements (Lines 303-305):

   • Mandate display of all message types before signing
   • Recommend max message count (e.g., ≤10)

Implementation Notes

• Reference Code (Line 309): Include test vectors for:
  • Odd/even leaf counts
  • Cross-implementation root consistency
• Typo Fix: "marketRoot" → "merkleRoot" (Lines 88, 255)

Conclusion

ERC-7920 has strong potential to standardize composite signatures. Addressing these points will ensure safe adoption across wallets and dapps. I’m available to collaborate on test vectors or implementation details.

Respectfully,
xinbenlv

[sola92]

@xinbenlv thanks a lot for review. Very helpful. I pushed the follow changes:

- Fix typos
- Hardened tree construction specification and added a reference implementation
- Add tests for the Merkle reference implementation, with cases for even/odd messages
-`abi.encodePacked` -> `abi.encode`
- Update specification to harden N=1 case

Happy to collaborate and make any more changes need. Thanks in advance!

[github-actions]

The commit 5beb332 (as a parent of 2eae175) contains errors.
Please inspect the Run Summary for details.

[sola92]

Thanks @SamWilsn. Changes pushed.

@poojaranjan could we add this to agenda for EIP Editing Office Hour Meeting 60

re-reviewed

[eip-review-bot]

All Reviewers Have Approved; Performing Automatic Merge...