bug: ...The usage of func : api.AssertIsLessOrEqual()

[George551556]

1. When i use the code "api.AssertIsLessOrEqual(v1, v2)", it always be true, even if the value of v1 is larger than v2.
2. As forthe code "api.AssertIsLessOrEqual(v1, 100)",it can run correctly and it can return fail when v1 is larger than 100
3. So I sense that the second argument of this func must be a constant_val, but why? It‘s a bug, or is it designed on purpose?
4. 是故意的还是不小心？

Expected Behavior

Actual Behavior

Possible Fix

Steps to Reproduce

Context

Your Environment

• gnark version used (e.g. v0.8.1, HEAD@develop):
• gnark-crypto version used:
• go version (e.g. 1.20.6):
• Operating System and version:

[readygo67]

I test the api.api.AssertIsLessOrEqual(v1, v2) in the following case. it works as expected.
maybe you can submit your code for further discussion.
my test gnark version is
"commit c36ff9e (HEAD -> master, origin/master, origin/HEAD)"

package less_or_equal

import (
	"fmt"
	"github.com/consensys/gnark-crypto/ecc"
	"github.com/consensys/gnark/backend/groth16"
	"github.com/consensys/gnark/frontend"
	"github.com/consensys/gnark/frontend/cs/r1cs"
	"github.com/consensys/gnark/test"
	"math/rand"
	"testing"
)

// Circuit defines a simple circuit
type Circuit struct {
	// struct tags on a variable is optional
	// default uses variable name and secret visibility.
	X frontend.Variable `gnark:"x"`
	Y frontend.Variable `gnark:"y"`
}

// Define declares the circuit constraints
func (circuit *Circuit) Define(api frontend.API) error {
	api.AssertIsLessOrEqual(circuit.X, circuit.Y)
	return nil
}

func TestCubic_LessOrEqual_BN254(t *testing.T) {
	field := ecc.BN254.ScalarField()
	assert := test.NewAssert(t)
	var circuit Circuit

	_r1cs, err := frontend.Compile(field, r1cs.NewBuilder, &circuit)
	assert.NoError(err)

	pk, vk, err := groth16.Setup(_r1cs)
	assert.NoError(err)

	//smaller success
	smaller := &Circuit{
		X: 3,
		Y: 4,
	}

	wit, err := frontend.NewWitness(smaller, ecc.BN254.ScalarField())
	assert.NoError(err)
	proof, err := groth16.Prove(_r1cs, pk, wit)
	assert.NoError(err)

	pubWit, err := wit.Public()
	assert.NoError(err)

	err = groth16.Verify(proof, vk, pubWit)
	if err != nil {
		fmt.Printf("err: %v\n", err)
	} else {
		fmt.Printf("verification pass\n")
	}

	//equal success
	equal := &Circuit{
		X: 3,
		Y: 3,
	}

	wit, err = frontend.NewWitness(equal, ecc.BN254.ScalarField())
	assert.NoError(err)
	proof, err = groth16.Prove(_r1cs, pk, wit)
	assert.NoError(err)

	pubWit, err = wit.Public()
	assert.NoError(err)

	err = groth16.Verify(proof, vk, pubWit)
	if err != nil {
		fmt.Printf("err: %v\n", err)
	} else {
		fmt.Printf("verification pass\n")
	}

	pubWit, err = wit.Public()
	assert.NoError(err)

	for i := 0; i < 100; i++ {
		y := rand.Int()
		x := rand.Intn(y + 1)
		fmt.Printf("i:%v, x: %v, y: %v\n", i, x, y)
		assignment := &Circuit{
			X: x,
			Y: y,
		}

		wit, err = frontend.NewWitness(assignment, ecc.BN254.ScalarField())
		assert.NoError(err)
		proof, err = groth16.Prove(_r1cs, pk, wit)
		assert.NoError(err)

		pubWit, err = wit.Public()
		assert.NoError(err)

		err = groth16.Verify(proof, vk, pubWit)
		if err != nil {
			fmt.Printf("err: %v\n", err)
		} else {
			fmt.Printf("verification pass\n")
		}
	}
}

[ivokub]

Yup, it would be better if you posted your non-working example.

PS! Converted to discussion as seems to be question about gnark usage, not an issue.

[George551556]

It is on the 37 and 38th line. It should be error when up_bound > left.

package main

import (
	"fmt"

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

const thousand int = 1000            // 10^3
const t_billion int = 1000000000000  // 10^12
const up_bound int = 6060000000000   // 6.06 * 10^12
const down_bound int = 5940000000000 // 5.94 * 10^12

type CubicCircuit struct {
	// struct tags on a variable is optional
	// default uses variable name and secret visibility.
	X frontend.Variable `gnark:"x"`
	Y frontend.Variable `gnark:",public"`
}

func (circuit *CubicCircuit) Define(api frontend.API) error {

	//对sigmoid展开到3阶 y(12-6x+3x*x-x*x*x)=6    assignment指定输入x和y时要变换为原来的1000倍
	//再转换为y=6/(12-6x+3x*x-x*x*x)  =>  y = 6/denom
	y := api.Div(circuit.Y, 1000)
	x1 := api.Div(circuit.X, 1000)
	x2 := api.Mul(x1, x1)
	x3 := api.Mul(x2, x1)
	denom := api.Add(12, api.Neg(api.Mul(6, x1)), api.Mul(3, x2), api.Neg(x3)) //代表原分式中右边的分母

	left := api.Mul(y, denom, t_billion)
	// 判断下限
	// api.AssertIsEqual(api.Cmp(left, down_bound), 1)
	api.Println(left, down_bound, up_bound)
	api.AssertIsLessOrEqual(up_bound, left) // this code should be err, but it actually not
	// 判断上限
	api.AssertIsLessOrEqual(left, up_bound)

	return nil
}

func main() {
	// compiles our circuit into a R1CS
	var circuit CubicCircuit
	ccs, _ := frontend.Compile(ecc.BN254.ScalarField(), r1cs.NewBuilder, &circuit)
	// groth16 zkSNARK: Setup
	pk, vk, _ := groth16.Setup(ccs)

	// witness definition 指定x和y的值
	assignment := CubicCircuit{X: 257, Y: 550} // Y允许范围：[559, 569]
	witness, _ := frontend.NewWitness(&assignment, ecc.BN254.ScalarField())
	publicWitness, _ := witness.Public()

	// groth16: Prove & Verify
	proof, _ := groth16.Prove(ccs, pk, witness)
	err := groth16.Verify(proof, vk, publicWitness)
	if err == nil {
		fmt.Println("verify success!!!")
	}
}

[George551556]

@readygo67 Sorry, I am unable to reproduce the error described at the beginning without the code above.

[ivokub]

Can you try again with the latest gnark? I.e. go get github.com/consensys/gnark@master? We recently fixed a bug related to AssertIsLessOrEqual: #1228. Maybe it was due to this.

Otherwise I'll check if there is an issue still with the latest gnark.

[George551556]

Yeah, it run as expected with the latest gnark. thank

[ivokub]

Thanks for reporting!