1# javascript implementation of zkSnark
  2
  3This is a javascript implementation of zkSnarks.
  4
  5This library allows to do the trusted setup,  generate proofs and verify the proofs.
  6
  7This library uses the compiled circuits generated by the jaz compiler.
  8
  9## Install
 10
 11```
 12npm install zkSnark
 13```
 14
 15## Usage
 16
 17### import
 18
 19```
 20const zkSnark = require("zksnark");
 21```
 22
 23### Load a circuit.
 24
 25```
 26// "myCircuit.cir" is the output of the jaz compiler
 27
 28const circuitDef = JSON.parse(fs.readFileSync("myCircuit.cir", "utf8"));
 29const circuit = new zkSnark.Circuit(circuitDef);
 30```
 31
 32### Inspect the circuit.
 33
 34```
 35    // `signalId` can always be a number or an alias string
 36
 37    circuit.nConstraints; // number of constraints
 38    circuit.nSignals; // number of signals
 39    circuit.nPublic; // number of public signals (nOutputs + nPublicInputs)
 40
 41    // The array of signals is always sorted in this order:
 42    // [ 1, outputs, publicInputs, privateInputs, internalSignals, constants]
 43
 44    // returns a,b and c coeficients of the `signalId` on a given `constraint`
 45    circuit.a(constraint, signalId)
 46    circuit.b(constraint, signalId)
 47    circuit.c(constraint, signalId)
 48
 49    circuit.nOutputs           // number of public outputs
 50    circuit.pubInputs          // number of public inputs
 51    circuit.nPrvInputs         // number of private inputs
 52    circuit.nInputs            // number of inputs ( nPublicInputs + nPrivateInputs)
 53    circuit.nVars              // number of variables ( not including constants (one is a variable) )
 54    circuit.nSignals           // number of signals ( including constants )
 55
 56    circuit.outputIdx(i)       // returns the index of the i'th output
 57    circuit.inputIdx(i)        // returns the index of the i'th input
 58    circuit.pubInputIdx(i)     // returns the index of the i'th public input
 59    circuit.prvInputIdx(i)     // returns the index of the i'th private input
 60    circuit.varIdx(i)          // returns the index of the i'th variable
 61    circuit.constantIdx(i)     // returns the index of the i'th constant
 62    circuit.signalIdx(i)       // returns the index of the i'th signal
 63
 64    // returns signal Idx given a signalId
 65    // if the idx >= n , it is a constant
 66    // if the idx == -1, the signal does not exist
 67    circuit.signalId2idx(signalId);
 68
 69    // returns an array aliases names for a given signalId
 70    circuit.signalNames(signalId)
 71
 72    // input is a key value object where keys are the signal names
 73    //   of all the inputs (public and private)
 74    // returns an array of values that represent the witness
 75    circuit.calculateWitness(input)
 76```
 77
 78### Trusted setup
 79
 80```
 81const setup = zkSnark.setup(circuit);
 82fs.writeFileSink("myCircuit.vk_proof", JSON.stringify(setup.vk_proof), "utf8");
 83fs.writeFileSink("myCircuit.vk_verifier", JSON.stringify(setup.vk_verifier), "utf8");
 84setup.toxic  // Must be discarded.
 85```
 86
 87### Generate proof
 88
 89```
 90const circuitDef = JSON.parse(fs.readFileSync("myCircuit.cir", "utf8"));
 91const circuit = new zkSnark.Circuit(circuitDef);
 92const input = {
 93    "main.pubIn1": "123",
 94    "main.out1": "456"
 95}
 96const witness = circuit.calculateWitness(input);
 97const vk_proof = JSON.parse(fs.readFileSync("myCircuit.vk_proof", "utf8"));
 98
 99const {proof, publicSignals} = zkSnark.genProof(vk_proof, witness);
100```
101
102### Verifier
103
104```
105const vk_verifier = JSON.parse(fs.readFileSync("myCircuit.vk_verifier", "utf8"));
106
107if (zkSnark.isValid(vk_verifier, proof, publicSignals)) {
108    console.log("The proof is valid");
109} else {
110    console.log("The proof is not valid");
111}
112```