Support obfuscated2

mtglib/internal/obfuscated2/frame.go

@@ -1 +1,79 @@
 package obfuscated2
+
+import (
+	"encoding/binary"
+	"fmt"
+	"io"
+)
+
+const (
+	handshakeFrameLen = 64
+
+	handshakeFrameLenKey   = 32
+	handshakeFrameLenIV    = 16
+	handshakeFrameLenMagic = 4
+	handshakeFrameLenDC    = 2
+
+	handshakeFrameOffsetStart = 8
+	handshakeFrameOffsetKey   = handshakeFrameOffsetStart
+	handshakeFrameOffsetIV    = handshakeFrameOffsetKey + handshakeFrameLenKey
+	handshakeFrameOffsetMagic = handshakeFrameOffsetIV + handshakeFrameLenIV
+	handshakeFrameOffsetDC    = handshakeFrameOffsetMagic + handshakeFrameLenMagic
+	handshakeFrameOffsetEnd   = handshakeFrameOffsetDC + handshakeFrameLenDC
+)
+
+// A structure of obfuscated2 handshake frame is following:
+//
+//    [frameOffsetFirst:frameOffsetKey:frameOffsetIV:frameOffsetMagic:frameOffsetDC:frameOffsetEnd].
+//
+//    - 8 bytes of noise
+//    - 32 bytes of AES Key
+//    - 16 bytes of AES IV
+//    - 4 bytes of 'magic' - this has some settings like a connection type
+//    - 2 bytes of 'DC'. DC is little endian int16
+//    - 2 bytes of noise
+type HandhakeFrame struct {
+	data [handshakeFrameLen]byte
+}
+
+func (f *HandhakeFrame) Fingerprint() []byte {
+	return f.data[handshakeFrameOffsetStart:handshakeFrameOffsetEnd]
+}
+
+func (f *HandhakeFrame) dc() int16 {
+	data := f.data[handshakeFrameOffsetDC:handshakeFrameOffsetEnd]
+
+	return int16(binary.LittleEndian.Uint16(data))
+}
+
+func (f *HandhakeFrame) key() []byte {
+	return f.data[handshakeFrameLenKey:handshakeFrameOffsetIV]
+}
+
+func (f *HandhakeFrame) iv() []byte {
+	return f.data[handshakeFrameOffsetIV:handshakeFrameOffsetMagic]
+}
+
+func (f *HandhakeFrame) magic() []byte {
+	return f.data[handshakeFrameOffsetMagic:handshakeFrameOffsetDC]
+}
+
+func (f *HandhakeFrame) invert() *HandhakeFrame {
+	newFrame := &HandhakeFrame{}
+
+	for i, v := range f.data {
+		newFrame.data[handshakeFrameLen-1-i] = v
+	}
+
+	return newFrame
+}
+
+func ReadHandshakeFrame(reader io.Reader) (*HandhakeFrame, error) {
+	frame := &HandhakeFrame{}
+
+	if _, err := io.ReadFull(reader, frame.data[:]); err != nil {
+		return nil, fmt.Errorf("cannot read frame data: %w", err)
+	}
+
+	return frame, nil
+}