Added VNC standard DES authentication

Author: mcclymont

client_auth_test.go

@@ -9,3 +9,11 @@ func TestClientAuthNone_Impl(t *testing.T) {
 		t.Fatal("ClientAuthNone doesn't implement ClientAuth")
 	}
 }
+
+func TestClientAuthVNC_Impl(t *testing.T) {
+	var raw interface{}
+	raw = new(ClientAuthVNC)
+	if _, ok := raw.(ClientAuth); !ok {
+		t.Fatal("ClientAuthVNC doesn't implement ClientAuth")
+	}
+}

client_auth_vnc.go

@@ -0,0 +1,55 @@
+package vnc
+
+import (
+	"crypto/des"
+	"encoding/binary"
+	"net"
+)
+
+// ClientAuthVNC is the standard password authentication
+type ClientAuthVNC struct {
+	Password string
+}
+
+func (*ClientAuthVNC) SecurityType() uint8 {
+	return 2
+}
+
+func (auth *ClientAuthVNC) Handshake(conn net.Conn) error {
+	// Read challenge block
+	var challenge [16]byte
+	if err := binary.Read(conn, binary.BigEndian, &challenge); err != nil {
+		return err
+	}
+
+	// Copy password string to 8 byte 0-padded slice
+	key := make([]byte, 8)
+	copy(key, auth.Password)
+
+	// Each byte of the password needs to be reversed. This is a
+	// non RFC-documented behaviour of VNC clients and servers
+	for i := range key {
+		key[i] = (key[i]&0x55)<<1 | (key[i]&0xAA)>>1 // Swap adjacent bits
+		key[i] = (key[i]&0x33)<<2 | (key[i]&0xCC)>>2 // Swap adjacent pairs
+		key[i] = (key[i]&0x0F)<<4 | (key[i]&0xF0)>>4 // Swap the 2 halves
+	}
+
+	cipher, err := des.NewCipher(key)
+	if err != nil {
+		return err
+	}
+
+	// Encrypt the challenge low 8 bytes then high 8 bytes
+	challengeLow := challenge[0:8]
+	challengeHigh := challenge[8:16]
+	cipher.Encrypt(challengeLow, challengeLow)
+	cipher.Encrypt(challengeHigh, challengeHigh)
+
+	// Send the encrypted challenge back to server
+	err = binary.Write(conn, binary.BigEndian, challenge)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}