Add new obfuscation package

mtglib/internal/obfuscation/handshake_frame.go

@@ -0,0 +1,111 @@
+package obfuscation
+
+import (
+	"crypto/rand"
+	"encoding/binary"
+	"slices"
+)
+
+// https://core.telegram.org/mtproto/mtproto-transports#transport-obfuscation
+const (
+	// default DC is nothing is selected
+	defaultDC = 2
+
+	// the length of the handshake frame. Always 64 bytes
+	hfLen = 64
+
+	hfLenKey            = 32
+	hfLenIV             = 16
+	hfLenConnectionType = 4
+
+	// A structure of obfuscated 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 'connection type' - this has some setting like a connection type
+	//	- 2 bytes of 'DC'. DC is little endian int16
+	//	- 2 bytes of noise
+	hfOffsetKey            = 8
+	hfOffsetIV             = hfOffsetKey + hfLenKey
+	hfOffsetConnectionType = hfOffsetIV + hfLenIV
+	hfOffsetDC             = hfOffsetConnectionType + hfLenConnectionType
+)
+
+// Connection-Type: Secure. We support only fake tls.
+var hfConnectionType = [hfLenConnectionType]byte{0xdd, 0xdd, 0xdd, 0xdd}
+
+type handshakeFrame struct {
+	data [hfLen]byte
+}
+
+func (h *handshakeFrame) key() []byte {
+	return h.data[hfOffsetKey : hfOffsetKey+hfLenKey]
+}
+
+func (h *handshakeFrame) iv() []byte {
+	return h.data[hfOffsetIV : hfOffsetIV+hfLenIV]
+}
+
+func (h *handshakeFrame) connectionType() []byte {
+	return h.data[hfOffsetConnectionType : hfOffsetConnectionType+hfLenConnectionType]
+}
+
+func (h *handshakeFrame) dcSlice() []byte {
+	return h.data[hfOffsetDC : hfOffsetDC+2]
+}
+
+func (h *handshakeFrame) dc() int {
+	idx := int16(binary.LittleEndian.Uint16(h.dcSlice()))
+
+	switch {
+	case idx > 0:
+		return int(idx)
+	case idx < 0:
+		return -int(idx)
+	}
+
+	return defaultDC
+}
+
+func (h *handshakeFrame) revert() {
+	slices.Reverse(h.data[hfOffsetKey:hfOffsetConnectionType])
+}
+
+func generateHandshake(dc int) handshakeFrame {
+	frame := handshakeFrame{}
+
+	for {
+		if _, err := rand.Read(frame.data[:]); err != nil {
+			panic(err)
+		}
+
+		// https://github.com/tdlib/td/blob/master/td/mtproto/TcpTransport.cpp#L157-L158.
+		if frame.data[0] == 0xef { // abridged header
+			// https://core.telegram.org/mtproto/mtproto-transports#abridged
+			continue
+		}
+
+		switch binary.LittleEndian.Uint32(frame.data[:4]) {
+		case 0x44414548, // HEAD
+			0x54534f50, // POST
+			0x20544547, // GET
+			0x4954504f, // OPTI
+			0x02010316, // ????
+			0xdddddddd, // PaddedIntermediate header
+			0xeeeeeeee: // Intermediate header
+			continue
+		}
+
+		if frame.data[4]|frame.data[5]|frame.data[6]|frame.data[7] == 0 {
+			continue
+		}
+
+		copy(frame.connectionType(), hfConnectionType[:])
+		binary.LittleEndian.PutUint16(frame.dcSlice(), uint16(dc))
+
+		return frame
+	}
+}