gnark

To create a zk-SNARK circuit, you must:

1. Define a struct that implements the frontend.Circuit interface by providing a Define(api frontend.API) error method.
2. Use struct tags (e.g., gnark:"x" or gnark:",public") to define circuit variables.
3. Compile the circuit using frontend.Compile.
4. Perform a setup (e.g., groth16.Setup) to generate proving and verification keys.
5. Create a witness using frontend.NewWitness with an assignment struct.
6. Generate a proof using groth16.Prove and verify it using groth16.Verify.

package main

import (
	"github.com/consensys/gnark-crypto/ecc"
	"github.com/consensys/gnark/backend/groth16"
	"github.com/consensys/gnark/frontend"
	"github.com/consensys/gnark/frontend/cs/r1cs"
)

// CubicCircuit defines a simple circuit.
// x**3 + x + 5 == y
type CubicCircuit struct {
	X frontend.Variable `gnark:"x"`
	Y frontend.Variable `gnark:",public"`
}

// Define declares the circuit constraints.
func (circuit *CubicCircuit) Define(api frontend.API) error {
	x3 := api.Mul(circuit.X, circuit.X, circuit.X)
	api.AssertIsEqual(circuit.Y, api.Add(x3, circuit.X, 5))
	return nil
}

func main() {
	var circuit CubicCircuit
	ccs, _ := frontend.Compile(ecc.BN254.ScalarField(), r1cs.NewBuilder, &circuit)

	pk, vk, _ := groth16.Setup(ccs)

	assignment := CubicCircuit{X: 3, Y: 35}
	witness, _ := frontend.NewWitness(&assignment, ecc.BN254.ScalarField())
	publicWitness, _ := witness.Public()

	proof, _ := groth16.Prove(ccs, pk, witness)
	_ = groth16.Verify(proof, vk, publicWitness)
}