tests/fuzzers/bls12381: fix blst deserializing (#25036)

* tests/fuzzers/bls12381: fix blst deserializing

* tests/fuzzers/bls12381: fix blst deserializing

Author: MariusVanDerWijden

tests/fuzzers/bls12381/bls12381_fuzz.go

@@ -29,6 +29,7 @@ import (
 	gnark "github.com/consensys/gnark-crypto/ecc/bls12-381"
 	"github.com/consensys/gnark-crypto/ecc/bls12-381/fp"
 	"github.com/consensys/gnark-crypto/ecc/bls12-381/fr"
+	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/crypto/bls12381"
 	blst "github.com/supranational/blst/bindings/go"
 )
@@ -70,7 +71,9 @@ func FuzzCrossPairing(data []byte) int {
 	blst.PairingRawAggregate(ctx, blG2, blG1)
 	blstResult := blst.PairingAsFp12(ctx)
 	if !(bytes.Equal(blstResult.ToBendian(), bls12381.NewGT().ToBytes(kResult))) {
-		panic("pairing mismatch blst / geth ")
+		fmt.Printf("geth: %v\n", common.Bytes2Hex(bls12381.NewGT().ToBytes(kResult)))
+		fmt.Printf("blst: %v\n", common.Bytes2Hex(blstResult.ToBendian()))
+		panic("pairing mismatch blst / geth")
 	}
 
 	return 1
@@ -227,10 +230,8 @@ func getG1Points(input io.Reader) (*bls12381.PointG1, *gnark.G1Affine, *blst.P1A
 	}
 
 	// marshal gnark point -> blst point
-	var p1 *blst.P1Affine
-	var scalar *blst.Scalar
-	scalar.Deserialize(s.Bytes())
-	p1.From(scalar)
+	scalar := new(blst.Scalar).FromBEndian(common.LeftPadBytes(s.Bytes(), 32))
+	p1 := new(blst.P1Affine).From(scalar)
 	if !bytes.Equal(p1.Serialize(), cpBytes) {
 		panic("bytes(blst.G1) != bytes(geth.G1)")
 	}
@@ -262,10 +263,9 @@ func getG2Points(input io.Reader) (*bls12381.PointG2, *gnark.G2Affine, *blst.P2A
 	}
 
 	// marshal gnark point -> blst point
-	var p2 *blst.P2Affine
-	var scalar *blst.Scalar
-	scalar.Deserialize(s.Bytes())
-	p2.From(scalar)
+	// Left pad the scalar to 32 bytes
+	scalar := new(blst.Scalar).FromBEndian(common.LeftPadBytes(s.Bytes(), 32))
+	p2 := new(blst.P2Affine).From(scalar)
 	if !bytes.Equal(p2.Serialize(), cpBytes) {
 		panic("bytes(blst.G2) != bytes(geth.G2)")
 	}