# 🦀 semaphore-rs
Rust support library for using [semaphore](https://github.com/appliedzkp/semaphore). It's mostly a Rust rewrite of [zk-kit](https://github.com/appliedzkp/zk-kit), but just focuses on semaphore (for now) and still covers a much smaller scope. It's using [ark-circom](https://github.com/gakonst/ark-circom) under the hood for generating the groth16 proofs.
## Usage
Add this line to your `cargo.toml`:
```toml
semaphore = { git = "https://github.com/worldcoin/semaphore-rs" }
```
## Building semaphore circuits
1. Check out submodule (if not done before already): `git submodule update --init --recursive`
1. Install semaphore dependencies `cd semaphore && npm install`
1. Compile circuits `npm exec ts-node ./scripts/compile-circuits.ts`
1. You'll find the `zkey` and `wasm` file in `semaphore/build/snark`
## Example
Example as in `src/lib.rs`, run with `cargo test`.
```rust,no_run
use semaphore_rs::{get_supported_depths, hash_to_field, Field, identity::Identity,
poseidon_tree::LazyPoseidonTree, protocol::*};
use num_bigint::BigInt;
// generate identity
let mut secret = *b"secret";
let id = Identity::from_secret(&mut secret, None);
// Get the first available tree depth. This is controlled by the crate features.
let depth = get_supported_depths()[0];
// generate merkle tree
let leaf = Field::from(0);
let mut tree = LazyPoseidonTree::new(depth, leaf).derived();
tree = tree.update(0, &id.commitment());
let merkle_proof = tree.proof(0);
let root = tree.root();
// change signal and external_nullifier here
let signal_hash = hash_to_field(b"xxx");
let external_nullifier_hash = hash_to_field(b"appId");
let nullifier_hash = generate_nullifier_hash(&id, external_nullifier_hash);
let proof = generate_proof(&id, &merkle_proof, external_nullifier_hash, signal_hash).unwrap();
let success = verify_proof(root, nullifier_hash, signal_hash, external_nullifier_hash, &proof, depth).unwrap();
assert!(success);
```