Revert "Use tgcrypto if available (#1715)"

This reverts commit 42cc9e61fb.

tgcrypto was made for Pyrogram, and seeing it used elsewhere
without much credit "hurts" the author. I personally do not endorse
its use, hence the lack of attention or notes in the documentation.

People who still want to benefit from the speed boost should go
out of their way to discover, install and patch Telethon's aes.py
module instead, all while complying with the respective license
(another reason to avoid said code in Telethon, which is under the
much more permissive MIT license).

People using tgcrypto for anything other than Pyrogram will do so
knowing full-well that this was not the library's intended usage.

telethon/crypto/aes.py

@@ -1,8 +1,7 @@
 """
 AES IGE implementation in Python.
 
-If available, tgcrypto will be used instead, otherwise
+If available, cryptg will be used instead, otherwise
-if available, cryptg will be used instead, otherwise
 if available, libssl will be used instead, otherwise
 the Python implementation will be used.
 """
@@ -16,19 +15,14 @@ __log__ = logging.getLogger(__name__)
 
 
 try:
-    import tgcrypto
-    __log__.debug('tgcrypto detected, it will be used for encryption')
-except ImportError:
-    tgcrypto = None
-    try:
     import cryptg
-        __log__.debug('cryptg detected, it will be used for encryption')
+    __log__.info('cryptg detected, it will be used for encryption')
-    except ImportError:
+except ImportError:
     cryptg = None
     if libssl.encrypt_ige and libssl.decrypt_ige:
-            __log__.debug('libssl detected, it will be used for encryption')
+        __log__.info('libssl detected, it will be used for encryption')
     else:
-            __log__.debug('tgcrypto or cryptg modules not installed and libssl not found, '
+        __log__.info('cryptg module not installed and libssl not found, '
                      'falling back to (slower) Python encryption')
 
 
@@ -43,8 +37,6 @@ class AES:
         Decrypts the given text in 16-bytes blocks by using the
         given key and 32-bytes initialization vector.
         """
-        if tgcrypto:
-            return tgcrypto.ige256_decrypt(cipher_text, key, iv)
         if cryptg:
             return cryptg.decrypt_ige(cipher_text, key, iv)
         if libssl.decrypt_ige:
@@ -86,8 +78,6 @@ class AES:
         if padding:
             plain_text += os.urandom(16 - padding)
 
-        if tgcrypto:
-            return tgcrypto.ige256_encrypt(plain_text, key, iv)
         if cryptg:
             return cryptg.encrypt_ige(plain_text, key, iv)
         if libssl.encrypt_ige:

telethon/crypto/aesctr.py

@@ -2,19 +2,6 @@
 This module holds the AESModeCTR wrapper class.
 """
 import pyaes
-import logging
-
-
-__log__ = logging.getLogger(__name__)
-
-
-try:
-    import tgcrypto
-    __log__.debug('tgcrypto detected, it will be used for ctr encryption')
-except ImportError:
-    tgcrypto = None
-    __log__.debug('tgcrypto module not installed, '
-                'falling back to (slower) Python encryption')
 
 
 class AESModeCTR:
@@ -29,9 +16,6 @@ class AESModeCTR:
         :param iv: the bytes initialization vector. Must have a length of 16.
         """
         # TODO Use libssl if available
-        if tgcrypto:
-            self._aes = (key, iv, bytearray(1))
-        else:
         assert isinstance(key, bytes)
         self._aes = pyaes.AESModeOfOperationCTR(key)
 
@@ -46,8 +30,6 @@ class AESModeCTR:
         :param data: the plain text to be encrypted.
         :return: the encrypted cipher text.
         """
-        if tgcrypto:
-            return tgcrypto.ctr256_encrypt(data, *self._aes)
         return self._aes.encrypt(data)
 
     def decrypt(self, data):
@@ -57,6 +39,4 @@ class AESModeCTR:
         :param data: the cipher text to be decrypted.
         :return: the decrypted plain text.
         """
-        if tgcrypto:
-            return tgcrypto.ctr256_decrypt(data, *self._aes)
         return self._aes.decrypt(data)