1# snarkjs: JavaScript implementation of zkSNARKs.
  2
  3This is a JavaScript implementation of zkSNARK schemes.
  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```sh
 12npm install snarkjs
 13```
 14
 15## Usage from command line.
 16
 17
 18```sh
 19snarkjs --help
 20```
 21
 22Will show all the info in how to use the cli.
 23
 24## Ussage from jacascript
 25
 26
 27### Import.
 28
 29```js
 30const zkSnark = require("snarkjs");
 31```
 32
 33### Load a circuit.
 34
 35```js
 36// "myCircuit.cir" is the output of the jaz compiler
 37
 38const circuitDef = JSON.parse(fs.readFileSync("myCircuit.cir", "utf8"));
 39const circuit = new zkSnark.Circuit(circuitDef);
 40```
 41
 42### Inspect the circuit.
 43
 44```js
 45    // `signalId` can always be a number or an alias string
 46
 47    circuit.nConstraints; // number of constraints
 48    circuit.nSignals; // number of signals
 49    circuit.nPublic; // number of public signals (nOutputs + nPublicInputs)
 50
 51    // The array of signals is always sorted in this order:
 52    // [ 1, outputs, publicInputs, privateInputs, internalSignals, constants]
 53
 54    // returns a,b and c coeficients of the `signalId` on a given `constraint`
 55    circuit.a(constraint, signalId)
 56    circuit.b(constraint, signalId)
 57    circuit.c(constraint, signalId)
 58
 59    circuit.nOutputs           // number of public outputs
 60    circuit.pubInputs          // number of public inputs
 61    circuit.nPrvInputs         // number of private inputs
 62    circuit.nInputs            // number of inputs ( nPublicInputs + nPrivateInputs)
 63    circuit.nVars              // number of variables ( not including constants (one is a variable) )
 64    circuit.nSignals           // number of signals ( including constants )
 65
 66    circuit.outputIdx(i)       // returns the index of the i'th output
 67    circuit.inputIdx(i)        // returns the index of the i'th input
 68    circuit.pubInputIdx(i)     // returns the index of the i'th public input
 69    circuit.prvInputIdx(i)     // returns the index of the i'th private input
 70    circuit.varIdx(i)          // returns the index of the i'th variable
 71    circuit.constantIdx(i)     // returns the index of the i'th constant
 72    circuit.signalIdx(i)       // returns the index of the i'th signal
 73
 74    // returns signal Idx given a signalId
 75    // if the idx >= n , it is a constant
 76    // if the idx == -1, the signal does not exist
 77    circuit.getSignalIdx(name);
 78
 79    // returns an array aliases names of the i'th signal
 80    circuit.signalNames(i)
 81
 82    // input is a key value object where keys are the signal names
 83    //   of all the inputs (public and private)
 84    // returns an array of values representing the witness
 85    circuit.calculateWitness(input)
 86```
 87
 88### Trusted setup.
 89
 90```js
 91const setup = zkSnark.setup(circuit);
 92fs.writeFileSync("myCircuit.vk_proof", JSON.stringify(setup.vk_proof), "utf8");
 93fs.writeFileSync("myCircuit.vk_verifier", JSON.stringify(setup.vk_verifier), "utf8");
 94setup.toxic  // Must be discarded.
 95```
 96
 97### Generate proof.
 98
 99```js
100const circuitDef = JSON.parse(fs.readFileSync("myCircuit.cir", "utf8"));
101const circuit = new zkSnark.Circuit(circuitDef);
102const input = {
103    "main.pubIn1": "123",
104    "main.out1": "456"
105}
106const witness = circuit.calculateWitness(input);
107const vk_proof = JSON.parse(fs.readFileSync("myCircuit.vk_proof", "utf8"));
108
109const {proof, publicSignals} = zkSnark.genProof(vk_proof, witness);
110```
111
112### Verifier.
113
114```js
115const vk_verifier = JSON.parse(fs.readFileSync("myCircuit.vk_verifier", "utf8"));
116
117if (zkSnark.isValid(vk_verifier, proof, publicSignals)) {
118    console.log("The proof is valid");
119} else {
120    console.log("The proof is not valid");
121}
122```
123
124## License
125
126snarkjs is part of the iden3 project copyright 2018 0KIMS association and published with GPL-3 license. Please check the COPYING file for more details.
127
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