Correct method for calculating Pedersen hash

[TheBojda]

I tried to calculate Pedersen hash with circom and circomjs, but the results are different.

This is my circuit:

template PedersenHasher() {
    signal input source;
    signal output hash;
    signal output hash2;

    component hasher = Pedersen(248);
    component sourceBits = Num2Bits(248);
    sourceBits.in <== source;

    for (var i = 0; i < 248; i++) {
        hasher.in[i] <== sourceBits.out[i];
    }

    hash <== hasher.out[0];
    hash2 <== hasher.out[1];
}

component main = PedersenHasher();

And this is my circomjs code:

const pedersen = await buildPedersenHash();
const source = crypto.randomBytes(31);

const pedersenHash = pedersen.hash(source)
const points = pedersen.babyJub.unpackPoint(pedersenHash)

const { proof, publicSignals } = await groth16.fullProve({ source: ethers.BigNumber.from(source).toString() },
    "./build/pedersenHasherTest_js/pedersenHasherTest.wasm", "./build/pedersenHasher_0001.zkey")

If am I right publicSignals[0] should be equal to points[0] and publicSignals[1] should be equal to points[1], but the hashes are different.

Am I doing something wrong, or is it a bug in circomjs?

[0pf0r]

Same issue here, have you found anything since then?

[TheBojda]

I don't use Pedersen, only MiMC and Poseidon. This is my final workaround. :)

[0pf0r]

Alright, I've read the related issue in the circomlib repo and been testing the suggestions there.
Very messy code but this should work:

const ffjavascript = require("ffjavascript");
const stringifyBigInts = ffjavascript.utils.stringifyBigInts;
const F = new ffjavascript.ZqField(
  ffjavascript.Scalar.fromString(
    "21888242871839275222246405745257275088548364400416034343698204186575808495617"
  )
);
var b = Buffer.alloc(32);
// Just set b to whatever input you want 

var h = pedersen.hash(b);
const hP = babyjub.unpackPoint(h)[0];

console.log((stringifyBigInts(F.fromRprLEM(hP))));

This should print the same hash circom logs during debugging (in decimal format obviously).
Also, here I used 256 bits long pedersen hash (not 248 like you), so buffer has to be 32 bytes long.