EcPrivKeyTweakMul (#13)

ecdh.go

@@ -196,3 +196,21 @@ func EcPubKeyCombine(ctx *Context, vPk []*PublicKey) (int, *PublicKey, error) {
 	}
 	return result, pkOut, nil
 }
+
+// EcPrivKeyTweakMul tweak a private key by multiplying it by a tweak. The return code is 0
+// if the tweak was out of range (chance of around 1 in 2^128 for uniformly
+// random 32-byte arrays) or zero. The code is 1 otherwise.
+func EcPrivKeyTweakMul(ctx *Context, seckey []byte, tweak []byte) (int, error) {
+	if len(tweak) != LenPrivateKey {
+		return 0, errors.New(ErrorTweakSize)
+	}
+	if len(seckey) != LenPrivateKey {
+		return 0, errors.New(ErrorPrivateKeySize)
+	}
+
+	result := int(C.secp256k1_ec_privkey_tweak_mul(ctx.ctx, (*C.uchar)(unsafe.Pointer(&seckey[0])), cBuf(tweak[:])))
+	if result != 1 {
+		return result, errors.New(ErrorTweakingPrivateKey)
+	}
+	return result, nil
+}

ecdh_test.go

@@ -56,7 +56,7 @@ func TestEcdh(t *testing.T) {
 
 }
 
-func TestPubKeyTweakAddFixtures(t *testing.T) {
+func TestPubKeyTweakAddF(t *testing.T) {
 	ctx, err := secp256k1.ContextCreate(secp256k1.ContextSign | secp256k1.ContextVerify)
 	if err != nil {
 		panic(err)
@@ -163,6 +163,50 @@ func TestPubKeyNegate(t *testing.T) {
 
 }
 
+func TestPrivKeyTweakMultiply(t *testing.T) {
+	ctx, err := secp256k1.ContextCreate(secp256k1.ContextSign | secp256k1.ContextVerify)
+	if err != nil {
+		panic(err)
+	}
+
+	file, err := ioutil.ReadFile("testdata/privkey_tweak_mult_vectors.json")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	var tests map[string]interface{}
+	err = json.Unmarshal(file, &tests)
+	if err != nil {
+		t.Error(err)
+	}
+
+	vectors := tests["tweak_mult"].([]interface{})
+
+
+	for _, testVector := range vectors {
+		v := testVector.(map[string]interface{})
+		privKeyBytes, err := hex.DecodeString(v["privkey"].(string))
+		if err != nil {
+			t.Error(err)
+		}
+
+		tweakBytes, err := hex.DecodeString(v["tweak"].(string))
+		if err != nil {
+			t.Error(err)
+		}
+
+		tweakedBytes, err := hex.DecodeString(v["tweaked"].(string))
+		if err != nil {
+			t.Error(err)
+		}
+
+		r, err := secp256k1.EcPrivKeyTweakMul(ctx, privKeyBytes, tweakBytes)
+		spOK(t, r, err)
+
+		assert.Equal(t, tweakedBytes, privKeyBytes)
+	}
+}
+
 func spOK(t *testing.T, result interface{}, err error) {
 	assert.NoError(t, err)
 	switch result := result.(type) {