Markle Path Retrieval MPC

This document can be seen as an appendix for:

• Scaling Semaphore

A proposed solution to scale the Semaphore protocol is to fetch the merkle path leaves using MPC.

The merkle path is the set of leaves and hashes involved in the calculation of the zero-knowledge inclusion proof.

Semaphore Group Tree (LeanIMT)

Properties

• Tree Type: LeanIMT (Lean Incremental Merkle Tree)
• Structure: Binary tree (2 leaves per branch)
• Leaf Size: 32 Bytes (BN254 Field Element)
• Maximum Depth: 32 levels
• Maximum Elements: 8,589,934,591 elements
• Maximum Size: 256 GB

MPC Circuit

• Inputs:
  • Element
  • Tree
• Outputs:
  • Sibling leaf (optional)
  • Merkle path hashes.