Completely get rid of addmod

[pygost.git] / pygost / gost28147.py

diff --git a/pygost/gost28147.py b/pygost/gost28147.py
index ce84dc2e6ea9bbb505995dfef42ac7403055a103..25c0f506a28d35b00fefc5e38c7416a6054d49f9 100644 (file)
--- a/pygost/gost28147.py
+++ b/pygost/gost28147.py
@@ -1,6 +1,6 @@
 # coding: utf-8
 # PyGOST -- Pure Python GOST cryptographic functions library
-# Copyright (C) 2015-2019 Sergey Matveev <stargrave@stargrave.org>
+# Copyright (C) 2015-2020 Sergey Matveev <stargrave@stargrave.org>
 #
 # This program is free software: you can redistribute it and/or modify
 # it under the terms of the GNU General Public License as published by
@@ -28,7 +28,7 @@ from pygost.gost3413 import pad_size
 from pygost.gost3413 import unpad2
 from pygost.utils import hexdec
 from pygost.utils import strxor
-from pygost.utils import xrange  # pylint: disable=redefined-builtin
+from pygost.utils import xrange
 
 
 KEYSIZE = 32
@@ -186,13 +186,6 @@ def ns2block(ns):
     )))
 
 
-def addmod(x, y, mod=2 ** 32):
-    """ Modulo adding of two integers
-    """
-    r = x + y
-    return r if r < mod else r - mod
-
-
 def _shift11(x):
     """ 11-bit cyclic shift
     """
@@ -236,7 +229,7 @@ def xcrypt(seq, sbox, key, ns):
     ]
     n1, n2 = ns
     for i in seq:
-        n1, n2 = _shift11(_K(s, addmod(n1, x[i]))) ^ n2, n1
+        n1, n2 = _shift11(_K(s, (n1 + x[i]) % (2 ** 32))) ^ n2, n1
     return n1, n2
 
 
@@ -373,8 +366,8 @@ def cnt(key, data, iv=8 * b"\x00", sbox=DEFAULT_SBOX):
     n2, n1 = encrypt(sbox, key, block2ns(iv))
     gamma = []
     for _ in xrange(0, len(data) + pad_size(len(data), BLOCKSIZE), BLOCKSIZE):
-        n1 = addmod(n1, C2, 2 ** 32)
-        n2 = addmod(n2, C1, 2 ** 32 - 1)
+        n1 = (n1 + C2) % (2 ** 32)
+        n2 = (n2 + C1) % (2 ** 32 - 1)
         gamma.append(ns2block(encrypt(sbox, key, (n1, n2))))
     return strxor(b"".join(gamma), data)