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Building your first ZKP program on Solana

Zeref on January 08, 2024

👋 Introduction Zero-knowledge proofs are a kind of security tool in cryptography. They let one person (the prover) show another person (...
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Pavlos Polianidis • • Edited

@zeref101 quick question. I've got a circuit with the following public inputs

  signal output out1[5];
  signal output address;
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When I create the proof.json it ends up having the following values:


[
"50",
"50",
"30",
"10",
"45",
"12737771764621907568098507625979260347390739857011548125897812973048106564980"
]
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out1 is basically an array with 5 bytes e.g. values between 0 and 255. The address output though is a poseidon hash. As I understand it's a big value in the Circom curve's Field set.

How do I pass this into the on-chain program? Do I call it this way?

const publicSignalsBuffer = publicSignals.map((i) => to32ByteBuffer(BigInt(i)))

Update

I can't get this example verity the ZKP successfully. It feels like the JS code is missing some transformation on the proof_a similar to what the rust code does here github.com/Lightprotocol/groth16-s...

For anyone interested, I have written a Rust crate and bundled it into wasm to use it directly in JS. Check it out here github.com/Apocentre/solana-zk-exa...

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Pavlos Polianidis •

This is an awesome article. Thanks for this tutorial. May I ask you if you can share the code for to32ByteBuffer?

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Pavlos Polianidis • • Edited

Ended up doing something like this:

const to32ByteBuffer = (num) => {
  const result = new Uint8Array(32);
  let i = 0;

  while (num > 0n) {
    result[i] = Number(num % 256n);
    num = num / 256n;
    i += 1;
  }

    return result;
}
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Zeref •

Thanks, Pavlos! Good catch on the missing code. I've updated the post. I'm not sure about your solution, but if it works, then great! 🙌