Hashing functions

Poseidon(x,y)=z for BN254 scalar field

This hash function is both compatible with Circom poseidon implementation (nInputs=2) and Noir Poseidon hash (std::hash::poseidon::hash::hash_2)

Below we show Noir and Cairo code computing the same hash.

main.nr

// For nargo < 1.0.0-beta.4:
use std::hash::poseidon::bn254::hash_2;

// For nargo >= 1.0.0-beta.4: (poseidon has been moved to a separate package)
// Add to Nargo.toml:
// [dependencies]
// poseidon = { tag = "v0.1.1", git = "https://github.com/noir-lang/poseidon" }
use poseidon::poseidon::bn254::hash_2;

fn main(x: Field, y: pub Field) {
    let x1 = [x, y];
    let z = hash_2(x1);
    assert(z == 7853200120776062878684798364095072458815029376092732009249414926327459813530);
}

#[test]
fn test_main() {
    main(1, 2);

    // Uncomment to make test fail
    // main(1, 1);
}

main.cairo

use garaga::hashes::poseidon_hash_2_bn254;

fn test_poseidon_bn254() {
    let x: u384 = u384 { limb0: 1, limb1: 0, limb2: 0, limb3: 0 };
    let y: u384 = u384 { limb0: 2, limb1: 0, limb2: 0, limb3: 0 };
    let z: u384 =
    7853200120776062878684798364095072458815029376092732009249414926327459813530_u256
    .into();

    assert_eq!(poseidon_hash_2_bn254(x, y), z);
}