Poseidon

This repository contains a reference implementations for the original version of Poseidon [1] and the instantiation as a hash function tuned for Filecoin [2]. Moreover, scripts to calculate the round numbers, the round constants, and the MDS matrices are also included.

Theoretical introduction

The set of parameters (t, M, p, alpha) fully specify a unique instance of Poseidon All other Poseidon parameters and constants are derived from these parameters.

The optimized Poseidon hash function is instantiated in the same way as the un-optimized algorithm, however the optimized Poseidon algorithm requires the additional pre-computation of round constants, pre-sparse matrix and sparse matrices. We implemented the pre-computation steps according to [2].

The hash function takes as input a list of elements from a certain field F and outputs o single field element. In addition, for this implementation the input_rate (size of input) parameter is required, which can take any value from 1 to t. A longer input size is possible and it is a work in progress.

Usage: generate new instance with pre-generated parameters

To create a new hash instance, you can use ready-made functions in parameters.py that have all the necessary parameters, or you can set your own parameters that have already been generated.

For matrices and round constants, use the hex representation.

import poseidon

def main():
    poseidon_simple, t = poseidon.parameters.case_simple()

    input_vec = [x for x in range(0, t)]
    print("Input: ", input_vec)
    poseidon_digest = poseidon_simple.run_hash(input_vec)
    print("Output: ", hex(int(poseidon_digest)))

    security_level = 128
    input_rate = 3
    t_opt = 4
    full_round = 8
    partial_round = 56
    alpha = 5
    poseidon_pre_generated = poseidon.OptimizedPoseidon(poseidon.HashType.CONSTINPUTLEN, poseidon.parameters.prime_255, 
                                                    security_level, alpha, input_rate, t_opt,
                                                    full_round=full_round, partial_round=partial_round,
                                                    rc_list=poseidon.parameters.round_constants_neptune, 
                                                    mds_matrix=poseidon.parameters.matrix_neptune)

    input_vec_2 = [x for x in range(0, t_opt - 1)]
    print("Input: ", input_vec_2)
    poseidon_output = poseidon_pre_generated.run_hash(input_vec_2)
    print("Output: ", hex(int(poseidon_output)))


if __name__ == "__main__":
    main()

Usage: generate new instance without pre-generated parameters

The number of rounds, roound constants and matrices are optional parameters; if they are not specified, they will be generated automatically. For the same required input parameters the same optional parameters will always be generated.

import poseidon

def main():
    security_level = 128
    input_rate = 3
    t = 4
    alpha = 5
    poseidon_new = poseidon.Poseidon(poseidon.parameters.prime_255, security_level, alpha, input_rate, t)

    input_vec = [x for x in range(0, t)]
    print("Input: ", input_vec)
    poseidon_output = poseidon_new.run_hash(input_vec)
    print("Output: ", hex(int(poseidon_output)))


if __name__ == "__main__":
    main()

Running tests

Test vectors and parameters for non-optimised implementation are taken from [3].

Parameter generation for the optimized Poseidon is checked using test vectors that are taken (in some cases generated) from the implementation of [2].

Running all tests

python3 -m pytest tests/

Running tests by file

python3 -m pytest tests/test_hash.py

Running a specific test. After :: you must enter the name of the specific test in the corresponding file

python3 -m pytest tests/test_hash.py::test_not_optimized_poseidon

License

The code is released under the MIT license. See LICENSE for more information.

Contact

Feel free to reach out!

[1] Poseidon: A New Hash Function for Zero-Knowledge Proof Systems. Cryptology ePrint Archive, Report 2019/458. https://eprint.iacr.org/2019/458. Accepted at USENIX'21.

[2] Neptune specification https://github.com/filecoin-project/neptune/tree/master/spec

[3] Reference Implementations for Various Versions of Starkad and Poseidon https://extgit.iaik.tugraz.at/krypto/hadeshash