Implement and use TCP obfuscated as a PoC (#112)

Credits to MadelineProto/Connection.php by @danog

telethon/crypto/__init__.py

@@ -1,4 +1,5 @@
 from .aes import AES
+from .aes_ctr import AESModeCTR
 from .auth_key import AuthKey
 from .factorization import Factorization
 from .cdn_decrypter import CdnDecrypter

telethon/crypto/aes_ctr.py

@@ -0,0 +1,29 @@
+import pyaes
+
+
+class AESModeCTR:
+    """Wrapper around pyaes.AESModeOfOperationCTR mode with custom IV"""
+    # TODO Maybe make a pull request to pyaes to support iv on CTR
+
+    def __init__(self, key, iv):
+        # TODO Use libssl if available
+        assert isinstance(key, bytes)
+        self._aes = pyaes.AESModeOfOperationCTR(key)
+
+        assert isinstance(iv, bytes)
+        assert len(iv) == 16
+        self.iv = iv
+        self._aes._counter._counter = list(self.iv)
+
+    def reset(self):
+        pass
+
+    def encrypt(self, data):
+        result = self._aes.encrypt(data)
+        self.reset()
+        return result
+
+    def decrypt(self, data):
+        result = self._aes.decrypt(data)
+        self.reset()
+        return result