Nim implementation of Poseidon2

Experimental implementation of the Poseidon 2 cryptographic hash function, specialized to BN254 and t=3. Uses the constantine library for cryptographic primitives. Neither completeness nor correctness are guaranteed at this moment in time.

Installation

Use the Nimble package manager to add poseidon2 to an existing project. Add the following to its .nimble file:

requires "poseidon2 >= 0.1.0 & < 0.2.0"

Usage

Hashing bytes into a field element with the sponge construction:

import poseidon2

let input = [1'u8, 2'u8, 3'u8] # some bytes that you want to hash
let digest: F = Sponge.digest(input) # a field element

Converting a field element into bytes:

let output: array[32, byte] = digest.toBytes

Combining field elements, useful for constructing a binary Merkle tree:

let left = Sponge.digest([1'u8, 2'u8, 3'u8])
let right = Sponge.digest([4'u8, 5'u8, 6'u8])
let combination = compress(left, right)

Compatbility

For Poseidon2, because of a historical accident, there are unfortunately TWO different sets of "standard" parameters, which is obviously bad for cross-project compatibility.

The switchover happened in commit #bb476b9ca38198cf5092487283c8b8c5d4317c4e in HorizenLab's reference repo. Both versions are safe to use though.

To resolve this issue, since version 0.1.1, we implement both sets (though the default is the "old" set of round constants, so that we are backward compatible. This may or may not change in the future.)

Links