secp256k1: Expose Jacobian point equivalency func.

dcrec/secp256k1/curve.go

@@ -149,6 +149,20 @@ func (p *JacobianPoint) ToAffine() {
 	p.Y.Normalize()
 }
 
+// EquivalentNonConst returns whether or not two Jacobian points represent the
+// same affine point in *non-constant* time.
+func (p *JacobianPoint) EquivalentNonConst(other *JacobianPoint) bool {
+	// Since the point at infinity is the identity element for the group, note
+	// that P = P + ∞ trivially implies that P - P = ∞.
+	//
+	// Use that fact to determine if the points represent the same affine point.
+	var result JacobianPoint
+	result.Set(p)
+	result.Y.Normalize().Negate(1).Normalize()
+	AddNonConst(&result, other, &result)
+	return (result.X.IsZero() && result.Y.IsZero()) || result.Z.IsZero()
+}
+
 // addZ1AndZ2EqualsOne adds two Jacobian points that are already known to have
 // z values of 1 and stores the result in the provided result param.  That is to
 // say result = p1 + p2.  It performs faster addition than the generic add

dcrec/secp256k1/bench_test.go → dcrec/secp256k1/curve_bench_test.go

@@ -167,46 +167,25 @@ func BenchmarkNAF(b *testing.B) {
 	}
 }
 
-// BenchmarkPubKeyDecompress benchmarks how long it takes to decompress the  y
-// coordinate from a given public key x coordinate.
-func BenchmarkPubKeyDecompress(b *testing.B) {
-	// Randomly generated keypair.
-	// Private key: 9e0699c91ca1e3b7e3c9ba71eb71c89890872be97576010fe593fbf3fd57e66d
-	pubKeyX := new(FieldVal).SetHex("d2e670a19c6d753d1a6d8b20bd045df8a08fb162cf508956c31268c6d81ffdab")
-
-	b.ReportAllocs()
-	b.ResetTimer()
-	var y FieldVal
-	for i := 0; i < b.N; i++ {
-		_ = DecompressY(pubKeyX, false, &y)
-	}
-}
-
-// BenchmarkParsePubKeyCompressed benchmarks how long it takes to parse a
-// compressed public key with an even y coordinate.
-func BenchmarkParsePubKeyCompressed(b *testing.B) {
-	format := "02"
-	x := "ce0b14fb842b1ba549fdd675c98075f12e9c510f8ef52bd021a9a1f4809d3b4d"
-	pubKeyBytes := hexToBytes(format + x)
-
-	b.ReportAllocs()
-	b.ResetTimer()
-	for i := 0; i < b.N; i++ {
-		ParsePubKey(pubKeyBytes)
-	}
-}
-
-// BenchmarkParsePubKeyUncompressed benchmarks how long it takes to parse an
-// uncompressed public key.
-func BenchmarkParsePubKeyUncompressed(b *testing.B) {
-	format := "04"
-	x := "11db93e1dcdb8a016b49840f8c53bc1eb68a382e97b1482ecad7b148a6909a5c"
-	y := "b2e0eaddfb84ccf9744464f82e160bfa9b8b64f9d4c03f999b8643f656b412a3"
-	pubKeyBytes := hexToBytes(format + x + y)
+// BenchmarkJacobianPointEquivalency benchmarks determining if two Jacobian
+// points represent the same affine point.
+func BenchmarkJacobianPointEquivalency(b *testing.B) {
+	// Create two Jacobian points with different Z values that represent the
+	// same affine point.
+	point1 := jacobianPointFromHex(
+		"d3e5183c393c20e4f464acf144ce9ae8266a82b67f553af33eb37e88e7fd2718",
+		"5b8f54deb987ec491fb692d3d48f3eebb9454b034365ad480dda0cf079651190",
+		"2",
+	)
+	point2 := jacobianPointFromHex(
+		"dcc3768780c74a0325e2851edad0dc8a566fa61a9e7fc4a34d13dcb509f99bc7",
+		"3503be6fb22abd76cb082f8aed63745b9149dd2b037728d32ebfebac99b51f17",
+		"3",
+	)
 
 	b.ReportAllocs()
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
-		ParsePubKey(pubKeyBytes)
+		point1.EquivalentNonConst(&point2)
 	}
 }