[−][src]Crate poseidon252

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Build Status ](https://travis-ci.com/dusk-network/Poseidon252) ](https://github.com/dusk-network/Poseidon252) ](https://dusk-network.github.io/Poseidon252/index.html)

Poseidon252

Reference implementation for the Poseidon Hashing algorithm.

Reference

Starkad and Poseidon: New Hash Functions for Zero Knowledge Proof Systems

This repository has been created so there's a unique library that holds the tools & functions required to perform Poseidon Hashes.

This hashes heavily rely on the Hades permutation, which is one of the key parts that Poseidon needs in order to work. This library uses the reference implementation of Hades252 which has been designed & build by the Dusk-Network team.

The library provides the two hashing techniques of Poseidon:

Sponge Hash

The Sponge techniqe in Poseidon allows to hash an unlimited ammount of data into a single Scalar. The sponge hash techniqe requires a padding to be applied before the data can be hashed.

This is done to avoid hash collitions as stated in the paper of the Poseidon Hash algorithm. See: (https://eprint.iacr.org/2019/458.pdf)[https://eprint.iacr.org/2019/458.pdf]. The inputs of the sponge_hash are always Scalar or need to be capable of being represented as it.

The module provides two sponge hash implementations:

Sponge hash using Scalar as backend. Which hashes the inputed Scalars and returns a single Scalar.
Sponge hash gadget using dusk_plonk::Variable as a backend. This techniqe is used/required when you want to proof pre-images of unconstrained data inside of Zero-Knowledge PLONK circuits.

Merkle Hash

The Merkle Level Hashing is a technique that Poseidon is optimized-by-design to perform. This technique allows us to perform hashes of an entire Merkle Tree using Hades252 as backend.

The technique requires the computation of a bitflags element which is always positioned as the first item of the level when we hash it, and it basically generated in respect of the presence or absence of a leaf in the tree level. This allows to prevent hashing collitions.

At the moment, this library is designed and optimized to work only with trees of ARITY up to 4. That means that trees with a bigger ARITY SHOULD NEVER be used with this lib. The module contains the implementation of 4 variants of the same algorithm to support the majority of the configurations that the user may need:

Scalar backend for hashing Merkle Tree levels outside of ZK-Circuits whith two variants: One of them computes the bitflags item while the other assumes that it has already been computed and placed in the first Level position.
dusk_plonk::Variable backend for hashing Merkle Tree levels inside of ZK-Circuits, specifically, PLONK circuits. This implementation comes also whith two variants; One of them computes the bitflags item while the other assumes that it has already been computed and placed in the first Level position.

Zero Knowledge Merkle Opening Proof example:

use poseidon252::{StorageScalar, PoseidonAnnotation};
use poseidon252::merkle_proof::merkle_opening_gadget;
use dusk_plonk::prelude::*;
use poseidon252::PoseidonTree;
use kelvin::{Blake2b, Compound};


// Generate Composer & Public Parameters
let pub_params =
    PublicParameters::setup(1 << 17, &mut rand::thread_rng()).unwrap();
let (ck, vk) = pub_params.trim(1 << 16).unwrap();
// Generate a tree with random scalars inside.
let mut ptree: PoseidonTree<_, Blake2b> = PoseidonTree::new(17);
for i in 0..1024u64 {
    ptree
        .push(StorageScalar(BlsScalar::from(i as u64)))
        .unwrap();
}

for i in [0u64, 567, 1023].iter() {
    let mut gadget_tester = |composer: &mut StandardComposer| {
        // We want to proof that we know the Scalar tied to the key Xusize
        // and that indeed, it is inside the merkle tree.

        // In this case, the key X corresponds to the Scalar(X).
        // We're supposing that we're provided with a Kelvin::Branch to perform
        // the proof.
        let branch = ptree.poseidon_branch(*i).unwrap().unwrap();

        // Get tree root.
        let root = ptree.root().unwrap();

        // Add the proven leaf value to the Constraint System
        let proven_leaf = composer.add_input(BlsScalar::from(*i));

        merkle_opening_gadget(composer, branch, proven_leaf, root);

        // Since we don't use all of the wires, we set some dummy constraints to avoid Committing
        // to zero polynomials.
        composer.add_dummy_constraints();
    };

    // Proving
    let mut prover = Prover::new(b"merkle_opening_tester");
    gadget_tester(prover.mut_cs());
    prover.preprocess(&ck).expect("Error on preprocessing");
    let proof = prover.prove(&ck).expect("Error on proving");

    // Verify
    let mut verifier = Verifier::new(b"merkle_opening_tester");
    gadget_tester(verifier.mut_cs());
    verifier.preprocess(&ck).expect("Error on preprocessing");
    assert!(verifier
        .verify(&proof, &vk, &vec![BlsScalar::zero()])
        .is_ok());
}

Standard Merkle Opening Proof example:

use poseidon252::{StorageScalar, PoseidonAnnotation};
use poseidon252::merkle_proof::merkle_opening_scalar_verification;
use dusk_plonk::bls12_381::Scalar as BlsScalar;
use kelvin::{Blake2b, Compound};
use poseidon252::PoseidonTree;

 // Generate a tree with random scalars inside.
let mut ptree: PoseidonTree<_, Blake2b> = PoseidonTree::new(17);
for i in 0..1024u64 {
    ptree
        .push(StorageScalar(BlsScalar::from(i as u64)))
        .unwrap();
}

for i in 0..1024u64 {
    // We want to proof that we know the Scalar tied to the key Xusize
    // and that indeed, it is inside the merkle tree.

    // In this case, the key X corresponds to the Scalar(X).
    // We're supposing that we're provided with a Kelvin::Branch to perform
    // the proof.
    let branch = ptree.poseidon_branch(i).unwrap().unwrap();

    // Get tree root.
    let root = ptree.root().unwrap();

    assert!(merkle_opening_scalar_verification(
        branch,
        root,
        BlsScalar::from(i),
    ));
}

If you want to contribute to this repository/project please, check CONTRIBUTING.md
If you want to report a bug or request a new feature addition, please open an issue on this repository.

Re-exports

pub use tree::PoseidonTree;

Modules

encrypt	Provides an encrypt and decrypt functionality
merkle_lvl_hash	Reference implementation for the Poseidon Merkle hash function Poseidon hash implementation
merkle_proof	Reference implementation for the gadget that builds a merkle opening proof
sponge	Reference implementation for the Poseidon Sponge hash function
tree	The module handling posedion-trees

Structs

PoseidonAnnotation	The annotation for the Notes tree is a storagescalar and a cardinality
PoseidonBranch	The `Poseidon` structure will accept a number of inputs equal to the arity.
PoseidonLevel	Represents a Merkle-Tree Level inside of a `PoseidonBranch`. It stores the leaves as `BlsScalar` and the offset which represents the position on the level where the hash of the previous `PoseidonLevel` is stored in.
StorageScalar	This struct is a Wrapper type over the bls12-381 `Scalar` which has implemented inside the logic to allows `Kelvin` Merkle Trees understand how to store `Scalar`s inside of their leaves.

Constants

ARITY

Maximum arity supported for trees.