zk-jwt-poc

Verify JWT (OIDC id_token) in smart contract, however privacy preserved with the aids of ZK

Overview

This repo's circuits mainly aim to show that:

∃ sub : (JWT = sub + nonce + iss + aud) ∧ (H(JWT) = Hjwt) ∧ (H(sub, salt) = Hsub)

Circuit() {
    signal input sub; // private input

    signal input nonce;
    signal input iss;
    signal input aud;

    signal input hJwt;
    signal input hSub;

    signal input salt; // private input

    signal output ok;

    component hashJWT = HashJWT()(sub, nonce, iss, aud);
    assert(Hjwt == hashJWT.hash);

    component hashSub = Hash()(sub, salt);
    assert(Hsub == hashSub.hash);

    output <== 1;
}

component main{public: [nonce, iss, aud, hJwt, hSub]} = Circuit();

Note that the actual implementation may differ.

Prerequisites

• Node.js (tested with v16.19.1)
• Circom

Also, we need npx.

$ npm install -g npx

The powers of tau file is used when generating zkey, so download one.

$ wget https://hermez.s3-eu-west-1.amazonaws.com/powersOfTau28_hez_final_19.ptau

Make sure to install node modules.

$ npm install

Build

Run below commands to compile circuits using circom:

$ mkdir build
$ circom jwt.circom --r1cs --wasm -o ./build

Run

Run below command to test JWT verification using ZK.

$ npx hardhat run jwt.js

The script includes the following steps:

1. Generate zkey from compiled ZK circuit
2. Calcuate witness
3. Generate ZK proof
4. Verify generated ZK proof (with snarkjs)
5. Generate solidity file for verifying JWT with ZK
6. Compile contracts
7. Deploy contracts
8. Verify JWT on-chain

The output shows times took in each steps.

Successfully verified JWT!
Summary:
init time:  1
zkey time:  60249
wtns time:  582
prove time:  4977
verify time:  189
sol time:  343
compile time:  39
deploy time:  1011
ZK verify time:  1226
(measure) dummy contract time:  10
(measure) RSA verify only time:  74
zkContract size: 2262
result: true

TODO

• Verify Poseidon hash
• Verify timestamps
• Use oracles for JWKS and time