snarkjs/README.md
2019-04-12 05:20:43 -07:00

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# snarkjs: JavaScript implementation of zkSNARKs.
This is a JavaScript implementation of zkSNARK schemes. It allows the original 8points protocol
and the Groth Protocol (3 point only and 3 pairings)
This library allows to do the trusted setup, generate proofs and verify the proofs.
This library uses the compiled circuits generated by the jaz compiler.
### Tutorial.
A good starting point [is this tutorial](https://github.com/iden3/circom/blob/master/TUTORIAL.md)
Also this [video](https://www.youtube.com/watch?v=-9TJa1hVsKA) is a good starting point.
## Install.
```sh
npm install snarkjs
```
## Usage from command line.
```sh
snarkjs --help
```
Will show all the info in how to use the cli.
## Usage from javascript
### Import.
```js
const zkSnark = require("snarkjs");
```
### Load a circuit.
```js
// "myCircuit.cir" is the output of the jaz compiler
const circuitDef = JSON.parse(fs.readFileSync("myCircuit.cir", "utf8"));
const circuit = new zkSnark.Circuit(circuitDef);
```
### Inspect the circuit.
```js
// `signalId` can always be a number or an alias string
circuit.nConstraints; // number of constraints
circuit.nSignals; // number of signals
circuit.nPublic; // number of public signals (nOutputs + nPublicInputs)
// The array of signals is always sorted in this order:
// [ 1, outputs, publicInputs, privateInputs, internalSignals, constants]
// returns a,b and c coeficients of the `signalId` on a given `constraint`
circuit.a(constraint, signalId)
circuit.b(constraint, signalId)
circuit.c(constraint, signalId)
circuit.nOutputs // number of public outputs
circuit.pubInputs // number of public inputs
circuit.nPrvInputs // number of private inputs
circuit.nInputs // number of inputs ( nPublicInputs + nPrivateInputs)
circuit.nVars // number of variables ( not including constants (one is a variable) )
circuit.nSignals // number of signals ( including constants )
circuit.outputIdx(i) // returns the index of the i'th output
circuit.inputIdx(i) // returns the index of the i'th input
circuit.pubInputIdx(i) // returns the index of the i'th public input
circuit.prvInputIdx(i) // returns the index of the i'th private input
circuit.varIdx(i) // returns the index of the i'th variable
circuit.constantIdx(i) // returns the index of the i'th constant
circuit.signalIdx(i) // returns the index of the i'th signal
// returns signal Idx given a signalId
// if the idx >= n , it is a constant
// if the idx == -1, the signal does not exist
circuit.getSignalIdx(name);
// returns an array aliases names of the i'th signal
circuit.signalNames(i)
// input is a key value object where keys are the signal names
// of all the inputs (public and private)
// returns an array of values representing the witness
circuit.calculateWitness(input)
```
### Trusted setup.
```js
const setup = zkSnark.setup(circuit);
fs.writeFileSync("myCircuit.vk_proof", JSON.stringify(setup.vk_proof), "utf8");
fs.writeFileSync("myCircuit.vk_verifier", JSON.stringify(setup.vk_verifier), "utf8");
setup.toxic // Must be discarded.
```
### Generate proof.
```js
const circuitDef = JSON.parse(fs.readFileSync("myCircuit.cir", "utf8"));
const circuit = new zkSnark.Circuit(circuitDef);
const input = {
"main.pubIn1": "123",
"main.out1": "456"
}
const witness = circuit.calculateWitness(input);
const vk_proof = JSON.parse(fs.readFileSync("myCircuit.vk_proof", "utf8"));
const {proof, publicSignals} = zkSnark.genProof(vk_proof, witness);
```
### Verifier.
```js
const vk_verifier = JSON.parse(fs.readFileSync("myCircuit.vk_verifier", "utf8"));
if (zkSnark.isValid(vk_verifier, proof, publicSignals)) {
console.log("The proof is valid");
} else {
console.log("The proof is not valid");
}
```
## License
snarkjs is part of the iden3 project copyright 2018 0KIMS association and published with GPL-3 license. Please check the COPYING file for more details.