Working version

obfuscated2/frame.go

@@ -0,0 +1,109 @@
+package obfuscated2
+
+import (
+	"bytes"
+	"crypto/rand"
+	"encoding/binary"
+	"io"
+
+	"github.com/juju/errors"
+)
+
+// https://blog.susanka.eu/how-telegram-obfuscates-its-mtproto-traffic/
+// [frameOffsetFirst:frameOffsetKey:frameOffsetIV:frameOffsetMagic:frameOffsetDC:frameOffsetEnd]
+const (
+	frameLenKey   = 32
+	frameLenIV    = 16
+	frameLenMagic = 4
+	frameLenDC    = 2
+
+	frameOffsetFirst = 8
+	frameOffsetKey   = frameOffsetFirst + frameLenKey
+	frameOffsetIV    = frameOffsetKey + frameLenIV
+	frameOffsetMagic = frameOffsetIV + frameLenMagic
+	frameOffsetDC    = frameOffsetMagic + frameLenDC
+
+	tgMagicByte = byte(239)
+
+	FrameLen = 64
+)
+
+var tgMagicBytes = []byte{tgMagicByte, tgMagicByte, tgMagicByte, tgMagicByte}
+
+type Frame []byte
+
+func (f Frame) Key() []byte {
+	return f[frameOffsetFirst:frameOffsetKey]
+}
+
+func (f Frame) IV() []byte {
+	return f[frameOffsetKey:frameOffsetIV]
+}
+
+func (f Frame) Magic() []byte {
+	return f[frameOffsetIV:frameOffsetMagic]
+}
+
+func (f Frame) DC() (n int16) {
+	buf := bytes.NewReader(f[frameOffsetMagic:frameOffsetDC])
+	binary.Read(buf, binary.LittleEndian, &n)
+
+	if n < 0 {
+		n = -n
+	} else if n == 0 {
+		n = 1
+	}
+
+	return n - 1
+}
+
+func (f Frame) Valid() bool {
+	return bytes.Equal(f.Magic(), tgMagicBytes)
+}
+
+func (f Frame) Invert() Frame {
+	reversed := make(Frame, FrameLen)
+	copy(reversed, f)
+
+	for i := 0; i < frameLenKey+frameLenIV; i++ {
+		reversed[frameOffsetFirst+i] = f[frameOffsetIV-1-i]
+	}
+
+	return reversed
+}
+
+func ExtractFrame(conn io.Reader) (Frame, error) {
+	buf := &bytes.Buffer{}
+	if _, err := io.CopyN(buf, conn, FrameLen); err != nil {
+		return nil, errors.Annotate(err, "Cannot extract obfuscated header")
+	}
+
+	return Frame(buf.Bytes()), nil
+}
+
+func generateFrame() Frame {
+	data := make(Frame, FrameLen)
+
+	for {
+		if _, err := rand.Read(data); err != nil {
+			continue
+		}
+		if data[0] == 0xef {
+			continue
+		}
+
+		val := (uint32(data[3]) << 24) | (uint32(data[2]) << 16) | (uint32(data[1]) << 8) | uint32(data[0])
+		if val == 0x44414548 || val == 0x54534f50 || val == 0x20544547 || val == 0x4954504f || val == 0xeeeeeeee {
+			continue
+		}
+
+		val = (uint32(data[7]) << 24) | (uint32(data[6]) << 16) | (uint32(data[5]) << 8) | uint32(data[4])
+		if val == 0x00000000 {
+			continue
+		}
+
+		copy(data.Magic(), tgMagicBytes)
+
+		return data
+	}
+}