Merge pull request #87 from Jigsaw-Code/bemasc-unpack

Use our own implementation of Pack for UDP

client/client.go

@@ -111,7 +111,7 @@ func (c *packetConn) WriteTo(b []byte, addr net.Addr) (int, error) {
 	// partially overlapping the plaintext and cipher slices since `Pack` skips the salt when calling
 	// `AEAD.Seal` (see https://golang.org/pkg/crypto/cipher/#AEAD).
 	plaintextBuf := append(append(cipherBuf[saltSize:saltSize], socksTargetAddr...), b...)
-	buf, err := shadowaead.Pack(cipherBuf, plaintextBuf, c.cipher)
+	buf, err := ss.Pack(cipherBuf, plaintextBuf, c.cipher)
 	if err != nil {
 		return 0, err
 	}

service/udp.go

@@ -446,7 +446,7 @@ func timedCopy(clientAddr net.Addr, clientConn net.PacketConn, targetConn *natco
 			//           [            packBuf             ]
 			//           [          buf           ]
 			packBuf := pkt[saltStart:]
-			buf, err := shadowaead.Pack(packBuf, plaintextBuf, targetConn.cipher) // Encrypt in-place
+			buf, err := ss.Pack(packBuf, plaintextBuf, targetConn.cipher) // Encrypt in-place
 			if err != nil {
 				return onet.NewConnectionError("ERR_PACK", "Failed to pack data to client", err)
 			}

shadowsocks/packet.go

@@ -27,6 +27,31 @@ var ErrShortPacket = errors.New("short packet")
 // This array must be at least service.maxNonceSize bytes.
 var zeroNonce [12]byte
 
+// Pack encrypts a Shadowsocks-UDP packet and returns a slice containing the encrypted packet.
+// dst must be big enough to hold the encrypted packet.
+// If plaintext and dst overlap but are not aligned for in-place encryption, this
+// function will panic.
+func Pack(dst, plaintext []byte, cipher shadowaead.Cipher) ([]byte, error) {
+	saltSize := cipher.SaltSize()
+	if len(dst) < saltSize {
+		return nil, io.ErrShortBuffer
+	}
+	salt := dst[:saltSize]
+	if err := RandomSaltGenerator.GetSalt(salt); err != nil {
+		return nil, err
+	}
+
+	aead, err := cipher.Encrypter(salt)
+	if err != nil {
+		return nil, err
+	}
+
+	if len(dst) < saltSize+len(plaintext)+aead.Overhead() {
+		return nil, io.ErrShortBuffer
+	}
+	return aead.Seal(salt, zeroNonce[:aead.NonceSize()], plaintext, nil), nil
+}
+
 // Unpack decrypts a Shadowsocks-UDP packet and returns a slice containing the decrypted payload or an error.
 // If dst is present, it is used to store the plaintext, and must have enough capacity.
 // If dst is nil, decryption proceeds in-place.