Move utils.calc_msg_key into auth_key (cyclic imports py3.4)

telethon/crypto/auth_key.py

@@ -4,7 +4,6 @@ This module holds the AuthKey class.
 import struct
 from hashlib import sha1
 
-from .. import helpers as utils
 from ..extensions import BinaryReader
 
 
@@ -36,4 +35,6 @@ class AuthKey:
         """
         new_nonce = new_nonce.to_bytes(32, 'little', signed=True)
         data = new_nonce + struct.pack('<BQ', number, self.aux_hash)
-        return utils.calc_msg_key(data)
+
+        # Calculates the message key from the given data
+        return sha1(data).digest()[4:20]

telethon/helpers.py

@@ -91,11 +91,6 @@ def calc_key(auth_key, msg_key, client):
     return aes_key, aes_iv
 
 
-def calc_msg_key(data):
-    """Calculates the message key from the given data"""
-    return sha1(data).digest()[4:20]
-
-
 def generate_key_data_from_nonce(server_nonce, new_nonce):
     """Generates the key data corresponding to the given nonce"""
     server_nonce = server_nonce.to_bytes(16, 'little', signed=True)