poseidon2 for evm

implementations of poseidon2 hash function (https://eprint.iacr.org/2023/323.pdf) in solidity, yul and huff.

attention: code in this repository has not been reviewed for security

install

forge install zemse/poseidon2-evm
npm install poseidon2-evm

usage

contracts:

• solidity: Poseidon2.sol
• yul: Poseidon2Yul.sol
• huff: Poseidon2.huff

any of the above contracts needs to be deployed on the network and then you can make calls to it. here is an example to hash two field elements:

contract MyContract {
    function myFunction() external returns (uint256) {
        uint256 result = 0xPoseidon2ContractAddress.call(
            abi.encode(
                0x1762d324c2db6a912e607fd09664aaa02dfe45b90711c0dae9627d62a4207788,
                0x1047bd52da536f6bdd26dfe642d25d9092c458e64a78211298648e81414cbf35
            )
        );
        return result;
    }
}

notes

solidity code is inefficient due to lot of memory usage and functions.

yul is generated using yul-generator.ts file and provides an inlined implementation that simply mutates 4 stack variables, uses no memory, which brings a lot of gas savings.

huff uses a dirty approach where SWAPs are avoided which leaves unused elements on stack. EVM allows the stack to grow upto 1024 until we run into stack overflow. for parameters (t=4, rf=8, rp=56), we would leave 4*(8+56) = 256 garbage elements on stack which is much lower than 1024 limit. this is similar to how solidity keeps garbage data on memory.

benchmarks

huff

gas cost for hashing one, two or three elements: 14934

yul benchmarks

gas cost for hasing one, two or three elements: 27517

solidity benchmarks

num elements	est gas
hash_1	219544
hash_2	220018
hash_3	220641
hash 4	416486
hash 5	417197
hash 6	417952
hash 7	604599
hash 8	605311
hash 9	606064
hash 10	792604