ZK-SNARKS with ZoKrates - problems with proving the hash preimage tutorial

Question

Just noticed today that ZoKrates has finally support for SHA256! I wanted to see it in action, so I followed the tutorial at https://zokrates.github.io/sha256example.html with a slight modification of the form

def main(private field a, private field b, private field c, private field d, field h0Pub, field h1Pub) -> (field):
    h0, h1 = sha256packed(a, b, c, d)
    h0 == h0Pub
    h1 == h1Pub
    return 1

./zokrates compute-witness -a 0 0 0 5 263561599766550617289250058199814760685 65303172752238645975888084098459749904

Witness, proof, and solidity verification contract can be created. However, if I try to send the proof with public inputs to the verification contract (verifyTx function) the function returns false.

Contracts are deployed and called with truffle 4.1.3 and tested on ganache-cli 6.1.0

Any idea/hint?

Answer 1

The problem was that input from proof.json was not in string hex representation like the rest of the fields.

"input" : [263561599766550617289250058199814760685,65303172752238645975888084098459749904,1] 

I passed this 1:1 as argument in truffle for verifyTx, which led to some precision loss.

After converting this to string hex representation everything worked fine!

"input":["0xc6481e22c5ff4164af680b8cfaa5e8ed","0x3120eeff89c4f307c4a6faaae059ce10","0x1"]

The call in truffle:

var p = require("./proof.json").proof;
var i = require("./proof.json").input;

verifier.verifyTx(p.A, p.A_p, p.B, p.B_p, p.C, p.C_p, p.H, p.K, i);