curve4q: Test showing DH does not fails on identity point.

Author: armfazh

dh/curve4q/curve4Q_test.go

@@ -7,6 +7,7 @@ import (
 	"io"
 	"testing"
 
+	"github.com/cloudflare/circl/ecc/fourq"
 	"github.com/cloudflare/circl/internal/test"
 )
 
@@ -37,6 +38,60 @@ func TestDH(t *testing.T) {
 	}
 }
 
+func TestDHLowOrder(t *testing.T) {
+	var secretAlice, validPublicAlice, invalidPublicAlice, sharedAlice Key
+	var secretBob, publicBob, sharedBob Key
+
+	t.Run("zeroPoint", func(t *testing.T) {
+		testTimes := 1 << 10
+
+		for i := 0; i < testTimes; i++ {
+			_, _ = rand.Read(secretAlice[:])
+			_, _ = rand.Read(secretBob[:])
+
+			KeyGen(&validPublicAlice, &secretAlice)
+			KeyGen(&publicBob, &secretBob)
+
+			zeroPoint := fourq.Point{}
+			zeroPoint.SetIdentity()
+			zeroPoint.Marshal((*[Size]byte)(&invalidPublicAlice))
+
+			ok := Shared(&sharedAlice, &secretAlice, &publicBob)
+			test.CheckOk(ok, "shared must not fail", t)
+
+			ok = Shared(&sharedBob, &secretBob, &validPublicAlice)
+			test.CheckOk(ok, "shared must not fail", t)
+
+			invalid := Shared(&sharedBob, &secretBob, &invalidPublicAlice)
+			test.CheckOk(!invalid, "shared must fail", t)
+		}
+	})
+
+	t.Run("lowOrderPoint", func(t *testing.T) {
+		KeyGen(&validPublicAlice, &secretAlice)
+		KeyGen(&publicBob, &secretBob)
+
+		// Point of order 56
+		lowOrderPoint := fourq.Point{
+			X: fourq.Fq{
+				fourq.Fp{0xc0, 0xe5, 0x21, 0x04, 0xaa, 0xe1, 0x93, 0xd8, 0x9b, 0x50, 0x42, 0x54, 0xd6, 0x46, 0x86, 0x74},
+				fourq.Fp{0x21, 0x25, 0x4d, 0x9a, 0xda, 0x8f, 0xad, 0x28, 0xa2, 0x3d, 0xfd, 0x02, 0x13, 0xea, 0xd2, 0x56},
+			},
+			Y: fourq.Fq{
+				fourq.Fp{0xaf, 0x71, 0xe4, 0x3b, 0x22, 0x21, 0x41, 0xef, 0x12, 0xba, 0x67, 0x02, 0x57, 0x1, 0xe5, 0x58},
+				fourq.Fp{0x0e, 0x1a, 0xf5, 0xe5, 0xb8, 0x24, 0x9c, 0xe0, 0xed, 0xc3, 0xc4, 0x69, 0x7, 0x32, 0x8e, 0x2c},
+			},
+		}
+
+		ok := lowOrderPoint.IsOnCurve()
+		test.CheckOk(ok, "point is on curve", t)
+
+		lowOrderPoint.Marshal((*[Size]byte)(&invalidPublicAlice))
+		invalid := Shared(&sharedBob, &secretBob, &invalidPublicAlice)
+		test.CheckOk(!invalid, "shared must fail", t)
+	})
+}
+
 func BenchmarkDH(b *testing.B) {
 	var secret, public, shared Key
 	_, _ = rand.Read(secret[:])