使用nodejs与sanrkjs生成零知识证明并进行验证

以Merkle Tree路径证明为例，使用nodejs与sanrkjs生成零知识证明，并进行本地验证。

版本

"circom": "0.0.35",
"circomlib": "0.0.20",
"snarkjs": "0.1.20"

源码

genKeypair.js
setup，生成pk和vk

const { compiler } = require("circom");
const { Circuit, groth ,stringifyBigInts } = require("snarkjs");
const path = require("path");
const fs = require("fs");

const genKeypair = async () => {
  console.log("start....");

  console.log("Get circtui definition....");
  const circuitDef = await compiler(
	path.join(__dirname, "./withdraw.circom"),{}
  );
  const circuit = new Circuit(circuitDef);

  console.log("Setup....");
  const {vk_proof,vk_verifier} = groth.setup(circuit);
  //save pk,vk file
  fs.writeFileSync("proving_key.json", JSON.stringify(stringifyBigInts(vk_proof)), 'utf8');
  fs.writeFileSync("verification_key.json", JSON.stringify(stringifyBigInts(vk_verifier)), 'utf8');

  console.log("finish....");
  process.exit(0);
};

genKeypair();

index.js
生成proof并进行本地验证

const { binarifyWitness } = require("./utils/binarify");
const bigInt = require("big-integer");
const { compiler } = require("circom");
const { Circuit, groth ,stringifyBigInts ,unstringifyBigInts} = require("snarkjs");
const path = require("path");
const fs = require("fs");

const SNARK_FIELD_SIZE = bigInt(
  "21888242871839275222246405745257275088548364400416034343698204186575808495617"
);

//read input
const fileData = fs.readFileSync('input.json');
const inputObj = JSON.parse(fileData);
const root = bigInt(inputObj.root);
const nullifierHash = bigInt(inputObj.nullifierHash);
const secret =  bigInt(inputObj.secret);
const paths2_root = [
	bigInt(inputObj.paths2_root[0]),
	bigInt(inputObj.paths2_root[1]),
	bigInt(inputObj.paths2_root[2])
];
const paths2_root_pos = bigInt(inputObj.paths2_root_pos);

const provingKey = require("./proving_key.json");
const verifyingKey = require("./verification_key.json");

//gen wintness proof
const generateProofAndVerify = async circuitInputs => {
  console.log("Get circtui definition....");
  const circuitDef = await compiler(
	path.join(__dirname, "./withdraw.circom"),{}
  );
  const circuit = new Circuit(circuitDef);

  console.log("loading pk,vk....");
  const vk_proof = unstringifyBigInts(provingKey);
  const vk_verifier = unstringifyBigInts(verifyingKey);

  console.log("Generating witness....");
  const witness = circuit.calculateWitness(stringifyBigInts(circuitInputs));
  //save witness file
  const witnessString = witness.map(x => x.toString());
  fs.writeFileSync("witness.json",JSON.stringify(witnessString));

  console.log("Generating proof and publicSignals....");
  const {proof,publicSignals} = await groth.genProof(vk_proof,witness);
  //save proof file
  const proofJson = JSON.stringify({
	    pi_a: stringifyBigInts(proof.pi_a).slice(0, 3),
		pi_b: stringifyBigInts(proof.pi_b).slice(0, 3),
		pi_c: stringifyBigInts(proof.pi_c).slice(0, 3),
		protocol: "groth"
	});
  fs.writeFileSync("proof.json", proofJson);
   //save public file
  console.log("Generating public.json....");
  const  pS = publicSignals.map(x => bigInt(x));
  const publicInputs = pS.map(x => x.mod(SNARK_FIELD_SIZE).toString());
  console.log("Generating public.json....");
  const publicJson = [
     publicInputs[0],publicInputs[1]
  ];
  fs.writeFileSync("public.json", JSON.stringify(publicJson));


  console.log("Check isValid....");
  const isValid = groth.isValid(vk_verifier,proof,publicSignals);
  console.log(`Passed local zk-snark verification: ${isValid}`);


  console.log("Generating solidityProof....");
  const solidityProof = {
    a: stringifyBigInts(proof.pi_a).slice(0, 2),
    b: stringifyBigInts(proof.pi_b).slice(0, 2),
    c: stringifyBigInts(proof.pi_c).slice(0, 2),
    inputs: publicInputs
  };
  //save solidityProof file
  fs.writeFileSync("solidityProof.json", JSON.stringify(solidityProof));

  //// Submit to smart contract
  //const solidityIsValid = await zkIdentityContract.isInGroup(
  //  solidityProof.a,
  //  solidityProof.b,
  //  solidityProof.c,
  //  solidityProof.inputs
  //);
  //console.log(`Verified user is in group (via solidity): ${solidityIsValid}`);

};

const main = async () => {
  console.log("zkp start....");

  await generateProofAndVerify({
    root: root,
    nullifierHash: nullifierHash,
	secret: secret,
	paths2_root: paths2_root,
	paths2_root_pos: paths2_root_pos
  });

  console.log("zkp finish....");
  process.exit(0);
};

main();

还可添加与verify.sol交互进行链上验证的部分。

完整代码放在我的github上面了。

遇到过的问题

1. Cannot read property’prime’ of undefined
   解决：compile()第二个参数写成{}
   
2. Circuit is not a constructor
   解决：改用旧版本的circom和snarkjs，circom的index.js改为module.exports.compiler = require("./src/compiler.js");
   
3. WebAssembly.Memory(): could not allocate memory
   解决：应该是电脑内存不够了，换成服务器运行ok
   
4. index.js运行过程中verify通过，使用命令行verify却失败
   解决：proof.json输出格式写错了
   

参考

https://www.jianshu.com/p/45ef81cc77b9
https://github.com/kendricktan/hello-world-zk-dapp