diff --git a/telethon/crypto/auth_key.py b/telethon/crypto/auth_key.py
index 679e62ff..a6c0675b 100644
--- a/telethon/crypto/auth_key.py
+++ b/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]
diff --git a/telethon/helpers.py b/telethon/helpers.py
index 82b551ab..9ca91e4f 100644
--- a/telethon/helpers.py
+++ b/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)
diff --git a/telethon_tests/crypto_test.py b/telethon_tests/crypto_test.py
index 022f0b3e..17453f62 100644
--- a/telethon_tests/crypto_test.py
+++ b/telethon_tests/crypto_test.py
@@ -99,13 +99,6 @@ class CryptoTests(unittest.TestCase):
         assert iv == expected_iv, 'Invalid IV (expected ("{}"), got ("{}"))'.format(
             expected_iv, iv)
 
-    @staticmethod
-    def test_calc_msg_key():
-        value = utils.calc_msg_key(b'Some random message')
-        expected = b'\xdfAa\xfc\x10\xab\x89\xd2\xfe\x19C\xf1\xdd~\xbf\x81'
-        assert value == expected, 'Value ("{}") does not equal expected ("{}")'.format(
-            value, expected)
-
     @staticmethod
     def test_generate_key_data_from_nonce():
         server_nonce = int.from_bytes(b'The 16-bit nonce', byteorder='little')