zcash-namada-airdrop

⚠️ Work in Progress: This project is under active development and not yet complete.

A toolkit for generating non-membership proofs for Zcash shielded assets as part of the Namada airdrop. This allows Zcash users with unspent shielded notes (Sapling or Orchard) to prove they held funds at a specific snapshot height without revealing their nullifiers.

What are Non-Membership Proofs?

A non-membership proof is a cryptographic proof that demonstrates a specific element (such as a nullifier) is not present in a given set, without revealing any additional information about the element itself. In the context of Zcash and this toolkit, non-membership proofs allow users to prove that their shielded note's nullifier does not appear in a snapshot of spent nullifiers. This enables users to show they held unspent funds at a particular block height, which is essential for privacy-preserving airdrops.

These proofs are constructed using Merkle trees built from the set of known nullifiers at the snapshot height. By providing a non-membership proof, a user can convince a verifier that their note was not spent (i.e., its nullifier is not in the tree).

Setup Instructions

Without nix

Prerequisites

• Rust 1.91+ (uses Rust 2024 edition)
• Protobuf compiler (protoc) - required for building the lightwalletd gRPC bindings

After cloning the repo:

git clone --branch v0.11.0 --single-branch https://github.com/zcash/orchard.git .patched-orchard
git -C .patched-orchard apply "../nix/airdrop-orchard-nullifier.patch"

git clone --branch v0.5.0 --single-branch https://github.com/zcash/sapling-crypto.git .patched-sapling-crypto
git -C .patched-sapling-crypto apply "../nix/airdrop-sapling-nullifier.patch"

curl -sL https://static.crates.io/crates/halo2_gadgets/halo2_gadgets-0.3.1.crate | tar xz
mv halo2_gadgets-0.3.1 .patched-halo2-gadgets
patch -p1 -d .patched-halo2-gadgets < nix/airdrop-halo2-gadgets-sha256.patch

Note: The patches expose private internals needed by the airdrop circuits - hiding nullifier derivation in sapling-crypto and orchard, circuit gadget visibility and note commitment helpers in orchard, and SHA-256 digest cell access in halo2_gadgets.

With nix

This workspace uses Nix to enhance the development experience.

• nix develop - enter the development environment
• nix fmt - format the workspace
• nix flake check - run checks, like linters and formatters. At the moment cargo clippy is not running with the other linters.

The workspace also uses pre-commit checks. These can be removed if they prove problematic.

Available Tools

zair

• Description: CLI tool for building Zcash airdrop snapshots, generating claim inputs/proofs, and verifying submissions.
  • zair key derive-seed / zair key derive-ufvk: derive seed.txt or ufvk.txt from a wallet mnemonic.
  • zair config build: build config.json, snapshot and gap-tree files.
  • zair claim prepare: scan chain for your notes and write claim-prepared.json (UFVK is provided via a file).
  • zair claim prove / zair claim sign / zair claim run: generate proofs and signed submissions.
  • zair verify proof / zair verify signature / zair verify run: verify proofs and signatures.
  • zair setup sapling / zair setup orchard: generate proving/verification parameters (organizers/developers).
  • Run with --help to check the usage.

Crates

• zair-core: Shared configuration and claim-input formats (JSON) used across the workspace.
• zair-sdk: Library/workflow crate used by zair (snapshot building, claim generation, proof helpers).
• zair-nonmembership: Nullifier and non-membership Merkle tree primitives used by the airdrop tools.
• zair-scan: lightwalletd integration + chain scanning used by the CLI (fetching nullifiers, scanning for notes, etc).
• zair-sapling-proofs: Sapling claim proving + verification API. Verification is available by default; proving is behind the prove feature (so verification-only consumers don't compile the circuit).
• zair-sapling-circuit: The Sapling claim circuit implementation (heavy; used only for keygen/proving).

Usage

Assuming that the project is set up correctly.

Building the Project

After completing the setup steps above, you can build the project. The project provides the zair binary:

cargo build --release

This will produce the optimized zair executable in the target/release directory.

User Guide

For a complete walkthrough of the airdrop claim process, see the Usage Guide.