Refactor and extract ring signature functionality to gotrax

constants.go

@@ -30,4 +30,21 @@ var kdfPrefix = []byte("OTRv4")
 const (
 	usageFingerprint = byte(0x00)
 	usageBraceKey    = byte(0x02)
+	usageAuth        = byte(0x11)
 )
+
+var basePointBytesDup = []byte{
+	0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66,
+	0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66,
+	0x66, 0x66, 0x66, 0x66, 0x33, 0x33, 0x33, 0x33, 0x33, 0x33, 0x33, 0x33,
+	0x33, 0x33, 0x33, 0x33, 0x33, 0x33, 0x33, 0x33, 0x33, 0x33, 0x33, 0x33,
+	0x33, 0x33, 0x33, 0x33, 0x33, 0x33, 0x33, 0x33, 0x00,
+}
+
+var primeOrderBytesDup = []byte{
+	0x3f, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+	0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+	0xff, 0xff, 0xff, 0xff, 0x7c, 0xca, 0x23, 0xe9, 0xc4, 0x4e, 0xdb, 0x49,
+	0xae, 0xd6, 0x36, 0x90, 0x21, 0x6c, 0xc2, 0x72, 0x8d, 0xc5, 0x8f, 0x55,
+	0x23, 0x78, 0xc2, 0x92, 0xab, 0x58, 0x44, 0xf3,
+}

kdf.go

@@ -2,6 +2,8 @@ package gotrax
 
 import "golang.org/x/crypto/sha3"
 
+type KdfFunc func(uint8, uint16, ...[]byte) []byte
+
 func KdfPrekeyServer(usageID uint8, size uint16, values ...[]byte) []byte {
 	buf := make([]byte, size)
 	KdfxPrekeyServer(usageID, buf, values...)

keys_serialize.go

@@ -48,6 +48,16 @@ func DeserializePoint(buf []byte) ([]byte, ed448.Point, bool) {
 	return buf[57:], tp, true
 }
 
+func DeserializeScalar(buf []byte) ([]byte, ed448.Scalar, bool) {
+	if len(buf) < 56 {
+		return nil, nil, false
+	}
+	ts := ed448.NewScalar()
+	ts.Decode(buf[0:56])
+	return buf[56:], ts, true
+
+}
+
 func (p *PublicKey) Deserialize(buf []byte) ([]byte, bool) {
 	var ok bool
 	pubKeyType := uint16(0)

keys_serialize_test.go

@@ -94,6 +94,22 @@ func (s *GotraxSuite) Test_EddsaSignature_deserializesCorrectly(c *C) {
 	c.Assert(r, DeepEquals, []byte{0x42})
 }
 
+func (s *GotraxSuite) Test_DeserializeScalar_failsOnShortBuffer(c *C) {
+	ser := []byte{
+		0x12, 0x34, 0x55, 0x00, 0x00, 0x00, 0x00, 0x0,
+		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x0,
+		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x0,
+		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x0,
+		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x0,
+		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x0,
+		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+	}
+
+	b, _, ok := DeserializeScalar(ser)
+	c.Assert(b, IsNil)
+	c.Assert(ok, Equals, false)
+}
+
 func (s *GotraxSuite) Test_EddsaSignature_failsOnShortDeserialize(c *C) {
 	ser := []byte{
 		0x12, 0x34, 0x55, 0x00, 0x00, 0x00, 0x00, 0x0,