crypto, tests/fuzzers: add gnark bn254 precompile methods for fuzzing (#30585)

Makes the gnark precompile methods more amenable to fuzzing
pull/30666/head
kevaundray 2 weeks ago committed by GitHub
parent 459bb4a647
commit 74461aecf6
No known key found for this signature in database
GPG Key ID: B5690EEEBB952194
  1. 51
      crypto/bn256/gnark/g1.go
  2. 38
      crypto/bn256/gnark/g2.go
  3. 65
      crypto/bn256/gnark/gt.go
  4. 73
      crypto/bn256/gnark/pairing.go
  5. 64
      tests/fuzzers/bn256/bn256_fuzz.go

@ -0,0 +1,51 @@
package bn256
import (
"math/big"
"github.com/consensys/gnark-crypto/ecc/bn254"
)
// G1 is the affine representation of a G1 group element.
//
// Since this code is used for precompiles, using Jacobian
// points are not beneficial because there are no intermediate
// points to allow us to save on inversions.
//
// Note: We also use this struct so that we can conform to the existing API
// that the precompiles want.
type G1 struct {
inner bn254.G1Affine
}
// Add adds `a` and `b` together, storing the result in `g`
func (g *G1) Add(a, b *G1) {
g.inner.Add(&a.inner, &b.inner)
}
// ScalarMult computes the scalar multiplication between `a` and
// `scalar`, storing the result in `g`
func (g *G1) ScalarMult(a *G1, scalar *big.Int) {
g.inner.ScalarMultiplication(&a.inner, scalar)
}
// Unmarshal deserializes `buf` into `g`
//
// Note: whether the deserialization is of a compressed
// or an uncompressed point, is encoded in the bytes.
//
// For our purpose, the point will always be serialized
// as uncompressed, ie 64 bytes.
//
// This method also checks whether the point is on the
// curve and in the prime order subgroup.
func (g *G1) Unmarshal(buf []byte) (int, error) {
return g.inner.SetBytes(buf)
}
// Marshal serializes the point into a byte slice.
//
// Note: The point is serialized as uncompressed.
func (p *G1) Marshal() []byte {
return p.inner.Marshal()
}

@ -0,0 +1,38 @@
package bn256
import (
"github.com/consensys/gnark-crypto/ecc/bn254"
)
// G2 is the affine representation of a G2 group element.
//
// Since this code is used for precompiles, using Jacobian
// points are not beneficial because there are no intermediate
// points and G2 in particular is only used for the pairing input.
//
// Note: We also use this struct so that we can conform to the existing API
// that the precompiles want.
type G2 struct {
inner bn254.G2Affine
}
// Unmarshal deserializes `buf` into `g`
//
// Note: whether the deserialization is of a compressed
// or an uncompressed point, is encoded in the bytes.
//
// For our purpose, the point will always be serialized
// as uncompressed, ie 128 bytes.
//
// This method also checks whether the point is on the
// curve and in the prime order subgroup.
func (g *G2) Unmarshal(buf []byte) (int, error) {
return g.inner.SetBytes(buf)
}
// Marshal serializes the point into a byte slice.
//
// Note: The point is serialized as uncompressed.
func (g *G2) Marshal() []byte {
return g.inner.Marshal()
}

@ -0,0 +1,65 @@
package bn256
import (
"fmt"
"math/big"
"github.com/consensys/gnark-crypto/ecc/bn254"
)
// GT is the affine representation of a GT field element.
//
// Note: GT is not explicitly used in mainline code.
// It is needed for fuzzing.
type GT struct {
inner bn254.GT
}
// Pair compute the optimal Ate pairing between a G1 and
// G2 element.
//
// Note: This method is not explicitly used in mainline code.
// It is needed for fuzzing. It should also be noted,
// that the output of this function may not match other
func Pair(a_ *G1, b_ *G2) *GT {
a := a_.inner
b := b_.inner
pairingOutput, err := bn254.Pair([]bn254.G1Affine{a}, []bn254.G2Affine{b})
if err != nil {
// Since this method is only called during fuzzing, it is okay to panic here.
// We do not return an error to match the interface of the other bn256 libraries.
panic(fmt.Sprintf("gnark/bn254 encountered error: %v", err))
}
return &GT{
inner: pairingOutput,
}
}
// Unmarshal deserializes `buf` into `g`
//
// Note: This method is not explicitly used in mainline code.
// It is needed for fuzzing.
func (g *GT) Unmarshal(buf []byte) error {
return g.inner.SetBytes(buf)
}
// Marshal serializes the point into a byte slice.
//
// Note: This method is not explicitly used in mainline code.
// It is needed for fuzzing.
func (g *GT) Marshal() []byte {
bytes := g.inner.Bytes()
return bytes[:]
}
// Exp raises `base` to the power of `exponent`
//
// Note: This method is not explicitly used in mainline code.
// It is needed for fuzzing.
func (g *GT) Exp(base GT, exponent *big.Int) *GT {
g.inner.Exp(base.inner, exponent)
return g
}

@ -0,0 +1,73 @@
package bn256
import (
"github.com/consensys/gnark-crypto/ecc/bn254"
)
// Computes the following relation: ∏ᵢ e(Pᵢ, Qᵢ) =? 1
//
// To explain why gnark returns a (bool, error):
//
// - If the function `e` does not return a result then internally
// an error is returned.
// - If `e` returns a result, then error will be nil,
// but if this value is not `1` then the boolean value will be false
//
// We therefore check for an error, and return false if its non-nil and
// then return the value of the boolean if not.
func PairingCheck(a_ []*G1, b_ []*G2) bool {
a := getInnerG1s(a_)
b := getInnerG2s(b_)
// Assume that len(a) == len(b)
//
// The pairing function will return
// false, if this is not the case.
size := len(a)
// Check if input is empty -- gnark will
// return false on an empty input, however
// the ossified behavior is to return true
// on an empty input, so we add this if statement.
if size == 0 {
return true
}
ok, err := bn254.PairingCheck(a, b)
if err != nil {
return false
}
return ok
}
// getInnerG1s gets the inner gnark G1 elements.
//
// These methods are used for two reasons:
//
// - We use a new type `G1`, so we need to convert from
// []*G1 to []*bn254.G1Affine
// - The gnark API accepts slices of values and not slices of
// pointers to values, so we need to return []bn254.G1Affine
// instead of []*bn254.G1Affine.
func getInnerG1s(pointerSlice []*G1) []bn254.G1Affine {
gnarkValues := make([]bn254.G1Affine, 0, len(pointerSlice))
for _, ptr := range pointerSlice {
if ptr != nil {
gnarkValues = append(gnarkValues, ptr.inner)
}
}
return gnarkValues
}
// getInnerG2s gets the inner gnark G2 elements.
//
// The rationale for this method is the same as `getInnerG1s`.
func getInnerG2s(pointerSlice []*G2) []bn254.G2Affine {
gnarkValues := make([]bn254.G2Affine, 0, len(pointerSlice))
for _, ptr := range pointerSlice {
if ptr != nil {
gnarkValues = append(gnarkValues, ptr.inner)
}
}
return gnarkValues
}

@ -22,12 +22,12 @@ import (
"io" "io"
"math/big" "math/big"
"github.com/consensys/gnark-crypto/ecc/bn254"
cloudflare "github.com/ethereum/go-ethereum/crypto/bn256/cloudflare" cloudflare "github.com/ethereum/go-ethereum/crypto/bn256/cloudflare"
gnark "github.com/ethereum/go-ethereum/crypto/bn256/gnark"
google "github.com/ethereum/go-ethereum/crypto/bn256/google" google "github.com/ethereum/go-ethereum/crypto/bn256/google"
) )
func getG1Points(input io.Reader) (*cloudflare.G1, *google.G1, *bn254.G1Affine) { func getG1Points(input io.Reader) (*cloudflare.G1, *google.G1, *gnark.G1) {
_, xc, err := cloudflare.RandomG1(input) _, xc, err := cloudflare.RandomG1(input)
if err != nil { if err != nil {
// insufficient input // insufficient input
@ -37,14 +37,14 @@ func getG1Points(input io.Reader) (*cloudflare.G1, *google.G1, *bn254.G1Affine)
if _, err := xg.Unmarshal(xc.Marshal()); err != nil { if _, err := xg.Unmarshal(xc.Marshal()); err != nil {
panic(fmt.Sprintf("Could not marshal cloudflare -> google: %v", err)) panic(fmt.Sprintf("Could not marshal cloudflare -> google: %v", err))
} }
xs := new(bn254.G1Affine) xs := new(gnark.G1)
if err := xs.Unmarshal(xc.Marshal()); err != nil { if _, err := xs.Unmarshal(xc.Marshal()); err != nil {
panic(fmt.Sprintf("Could not marshal cloudflare -> gnark: %v", err)) panic(fmt.Sprintf("Could not marshal cloudflare -> gnark: %v", err))
} }
return xc, xg, xs return xc, xg, xs
} }
func getG2Points(input io.Reader) (*cloudflare.G2, *google.G2, *bn254.G2Affine) { func getG2Points(input io.Reader) (*cloudflare.G2, *google.G2, *gnark.G2) {
_, xc, err := cloudflare.RandomG2(input) _, xc, err := cloudflare.RandomG2(input)
if err != nil { if err != nil {
// insufficient input // insufficient input
@ -54,14 +54,14 @@ func getG2Points(input io.Reader) (*cloudflare.G2, *google.G2, *bn254.G2Affine)
if _, err := xg.Unmarshal(xc.Marshal()); err != nil { if _, err := xg.Unmarshal(xc.Marshal()); err != nil {
panic(fmt.Sprintf("Could not marshal cloudflare -> google: %v", err)) panic(fmt.Sprintf("Could not marshal cloudflare -> google: %v", err))
} }
xs := new(bn254.G2Affine) xs := new(gnark.G2)
if err := xs.Unmarshal(xc.Marshal()); err != nil { if _, err := xs.Unmarshal(xc.Marshal()); err != nil {
panic(fmt.Sprintf("Could not marshal cloudflare -> gnark: %v", err)) panic(fmt.Sprintf("Could not marshal cloudflare -> gnark: %v", err))
} }
return xc, xg, xs return xc, xg, xs
} }
// fuzzAdd fuzzez bn256 addition between the Google and Cloudflare libraries. // fuzzAdd fuzzes bn256 addition between the Google, Cloudflare and Gnark libraries.
func fuzzAdd(data []byte) int { func fuzzAdd(data []byte) int {
input := bytes.NewReader(data) input := bytes.NewReader(data)
xc, xg, xs := getG1Points(input) xc, xg, xs := getG1Points(input)
@ -72,7 +72,7 @@ func fuzzAdd(data []byte) int {
if yc == nil { if yc == nil {
return 0 return 0
} }
// Ensure both libs can parse the second curve point // Ensure libs can parse the second curve point
// Add the two points and ensure they result in the same output // Add the two points and ensure they result in the same output
rc := new(cloudflare.G1) rc := new(cloudflare.G1)
rc.Add(xc, yc) rc.Add(xc, yc)
@ -80,9 +80,8 @@ func fuzzAdd(data []byte) int {
rg := new(google.G1) rg := new(google.G1)
rg.Add(xg, yg) rg.Add(xg, yg)
tmpX := new(bn254.G1Jac).FromAffine(xs) rs := new(gnark.G1)
tmpY := new(bn254.G1Jac).FromAffine(ys) rs.Add(xs, ys)
rs := new(bn254.G1Affine).FromJacobian(tmpX.AddAssign(tmpY))
if !bytes.Equal(rc.Marshal(), rg.Marshal()) { if !bytes.Equal(rc.Marshal(), rg.Marshal()) {
panic("add mismatch: cloudflare/google") panic("add mismatch: cloudflare/google")
@ -94,8 +93,8 @@ func fuzzAdd(data []byte) int {
return 1 return 1
} }
// fuzzMul fuzzez bn256 scalar multiplication between the Google and Cloudflare // fuzzMul fuzzes bn256 scalar multiplication between the Google, Cloudflare
// libraries. // and Gnark libraries.
func fuzzMul(data []byte) int { func fuzzMul(data []byte) int {
input := bytes.NewReader(data) input := bytes.NewReader(data)
pc, pg, ps := getG1Points(input) pc, pg, ps := getG1Points(input)
@ -122,15 +121,13 @@ func fuzzMul(data []byte) int {
rg := new(google.G1) rg := new(google.G1)
rg.ScalarMult(pg, new(big.Int).SetBytes(buf)) rg.ScalarMult(pg, new(big.Int).SetBytes(buf))
rs := new(bn254.G1Jac) rs := new(gnark.G1)
psJac := new(bn254.G1Jac).FromAffine(ps) rs.ScalarMult(ps, new(big.Int).SetBytes(buf))
rs.ScalarMultiplication(psJac, new(big.Int).SetBytes(buf))
rsAffine := new(bn254.G1Affine).FromJacobian(rs)
if !bytes.Equal(rc.Marshal(), rg.Marshal()) { if !bytes.Equal(rc.Marshal(), rg.Marshal()) {
panic("scalar mul mismatch: cloudflare/google") panic("scalar mul mismatch: cloudflare/google")
} }
if !bytes.Equal(rc.Marshal(), rsAffine.Marshal()) { if !bytes.Equal(rc.Marshal(), rs.Marshal()) {
panic("scalar mul mismatch: cloudflare/gnark") panic("scalar mul mismatch: cloudflare/gnark")
} }
return 1 return 1
@ -150,17 +147,26 @@ func fuzzPair(data []byte) int {
// Pair the two points and ensure they result in the same output // Pair the two points and ensure they result in the same output
clPair := cloudflare.Pair(pc, tc).Marshal() clPair := cloudflare.Pair(pc, tc).Marshal()
gPair := google.Pair(pg, tg).Marshal() gPair := google.Pair(pg, tg).Marshal()
sPair := gnark.Pair(ps, ts).Marshal()
if !bytes.Equal(clPair, gPair) { if !bytes.Equal(clPair, gPair) {
panic("pairing mismatch: cloudflare/google") panic("pairing mismatch: cloudflare/google")
} }
cPair, err := bn254.Pair([]bn254.G1Affine{*ps}, []bn254.G2Affine{*ts})
if err != nil { normalizedClPair := normalizeGTToGnark(clPair).Marshal()
panic(fmt.Sprintf("gnark/bn254 encountered error: %v", err)) if !bytes.Equal(normalizedClPair, sPair) {
panic("pairing mismatch: cloudflare/gnark")
} }
// gnark uses a different pairing algorithm which might produce return 1
// different but also correct outputs, we need to scale the output by s }
// normalizeGTToGnark scales a Cloudflare/Google GT element by `s`
// so that it can be compared with a gnark GT point.
//
// For the definition of `s` see 3.5 in https://eprint.iacr.org/2015/192.pdf
func normalizeGTToGnark(cloudflareOrGoogleGT []byte) *gnark.GT {
// Compute s = 2*u(6*u^2 + 3*u + 1)
u, _ := new(big.Int).SetString("0x44e992b44a6909f1", 0) u, _ := new(big.Int).SetString("0x44e992b44a6909f1", 0)
u_exp2 := new(big.Int).Exp(u, big.NewInt(2), nil) // u^2 u_exp2 := new(big.Int).Exp(u, big.NewInt(2), nil) // u^2
u_6_exp2 := new(big.Int).Mul(big.NewInt(6), u_exp2) // 6*u^2 u_6_exp2 := new(big.Int).Mul(big.NewInt(6), u_exp2) // 6*u^2
@ -170,14 +176,12 @@ func fuzzPair(data []byte) int {
u_2 := new(big.Int).Mul(big.NewInt(2), u) // 2*u u_2 := new(big.Int).Mul(big.NewInt(2), u) // 2*u
s := u_2.Mul(u_2, inner) // 2*u(6*u^2 + 3*u + 1) s := u_2.Mul(u_2, inner) // 2*u(6*u^2 + 3*u + 1)
gRes := new(bn254.GT) // Scale the Cloudflare/Google GT element by `s`
if err := gRes.SetBytes(clPair); err != nil { gRes := new(gnark.GT)
if err := gRes.Unmarshal(cloudflareOrGoogleGT); err != nil {
panic(err) panic(err)
} }
gRes = gRes.Exp(*gRes, s) gRes = gRes.Exp(*gRes, s)
if !bytes.Equal(cPair.Marshal(), gRes.Marshal()) {
panic("pairing mismatch: cloudflare/gnark")
}
return 1 return gRes
} }

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