Add required things for middlehandshake

wrappers/blockcipher.go

@@ -148,7 +148,7 @@ func (w *wrapperBlockCipher) RemoteAddr() *net.TCPAddr {
 	return w.parent.RemoteAddr()
 }
 
-func NewBlockCipher(parent StreamReadWriteCloser, encryptor, decryptor cipher.BlockMode) StreamReadWriteCloser {
+func newBlockCipher(parent StreamReadWriteCloser, encryptor, decryptor cipher.BlockMode) StreamReadWriteCloser {
 	return &wrapperBlockCipher{
 		parent:    parent,
 		encryptor: encryptor,

wrappers/mtproto_cipher.go

@@ -0,0 +1,111 @@
+package wrappers
+
+import (
+	"bytes"
+	"crypto/aes"
+	"crypto/cipher"
+	"crypto/md5"
+	"crypto/sha1"
+	"encoding/binary"
+	"net"
+
+	"github.com/9seconds/mtg/mtproto/rpc"
+	"github.com/9seconds/mtg/utils"
+)
+
+type mtprotoCipherPurpose uint8
+
+const (
+	mtprotoCipherPurposeClient mtprotoCipherPurpose = iota
+	mtprotoCipherPurposeServer
+)
+
+var mtprotoEmptyIP = [4]byte{0x00, 0x00, 0x00, 0x00}
+
+func NewMiddleProxyCipher(parent StreamReadWriteCloser,
+	req *rpc.NonceRequest,
+	resp *rpc.NonceResponse,
+	secret []byte) StreamReadWriteCloser {
+	localAddr := parent.LocalAddr()
+	remoteAddr := parent.RemoteAddr()
+
+	encKey, encIV := mtprotoDeriveKeys(mtprotoCipherPurposeClient,
+		req,
+		resp,
+		localAddr,
+		remoteAddr,
+		secret)
+	decKey, decIV := mtprotoDeriveKeys(mtprotoCipherPurposeServer,
+		req,
+		resp,
+		localAddr,
+		remoteAddr,
+		secret)
+
+	enc, _ := mtprotoMakeEncrypterDecrypter(encKey, encIV)
+	_, dec := mtprotoMakeEncrypterDecrypter(decKey, decIV)
+
+	return newBlockCipher(parent, enc, dec)
+}
+
+func mtprotoDeriveKeys(purpose mtprotoCipherPurpose,
+	req *rpc.NonceRequest,
+	resp *rpc.NonceResponse,
+	client, remote *net.TCPAddr,
+	secret []byte) ([]byte, []byte) {
+	message := bytes.Buffer{}
+	message.Write(resp.Nonce)   // nolint: gosec
+	message.Write(req.Nonce)    // nolint: gosec
+	message.Write(req.CryptoTS) // nolint: gosec
+
+	clientIPv4 := mtprotoEmptyIP[:]
+	serverIPv4 := mtprotoEmptyIP[:]
+	if client.IP.To4() != nil {
+		clientIPv4 = utils.ReverseBytes(client.IP.To4())
+		serverIPv4 = utils.ReverseBytes(remote.IP.To4())
+	}
+	message.Write(serverIPv4) // nolint: gosec
+
+	var port [2]byte
+	binary.LittleEndian.PutUint16(port[:], uint16(client.Port))
+	message.Write(port[:]) // nolint: gosec
+
+	switch purpose {
+	case mtprotoCipherPurposeClient:
+		message.WriteString("CLIENT") // nolint: gosec
+	case mtprotoCipherPurposeServer:
+		message.WriteString("SERVER") // nolint: gosec
+	default:
+		panic("Unexpected cipher purpose")
+	}
+
+	message.Write(clientIPv4) // nolint: gosec
+	binary.LittleEndian.PutUint16(port[:], uint16(remote.Port))
+	message.Write(port[:])    // nolint: gosec
+	message.Write(secret)     // nolint: gosec
+	message.Write(resp.Nonce) // nolint: gosec
+
+	if client.IP.To4() == nil {
+		message.Write(client.IP.To16()) // nolint: gosec
+		message.Write(remote.IP.To16()) // nolint: gosec
+	}
+	message.Write(req.Nonce) // nolint: gosec
+
+	data := message.Bytes()
+	md5sum := md5.Sum(data[1:]) // nolint: gas
+	sha1sum := sha1.Sum(data)   // nolint: gosec
+
+	key := append(md5sum[:12], sha1sum[:]...)
+	iv := md5.Sum(data[2:]) // nolint: gas
+
+	return key, iv[:]
+}
+
+func mtprotoMakeEncrypterDecrypter(key, iv []byte) (cipher.BlockMode, cipher.BlockMode) {
+	block, err := aes.NewCipher(key)
+	if err != nil {
+		panic(err)
+	}
+
+	return cipher.NewCBCEncrypter(block, iv), cipher.NewCBCDecrypter(block, iv)
+}