Completely get rid of addmod

[pygost.git] / pygost / gost28147.py

diff --git a/pygost/gost28147.py b/pygost/gost28147.py
index b6f3cf49b6fa80a78918e7c411fab8b72f4effbd..25c0f506a28d35b00fefc5e38c7416a6054d49f9 100644 (file)
--- a/pygost/gost28147.py
+++ b/pygost/gost28147.py
@@ -186,12 +186,6 @@ def ns2block(ns):
     )))
 
 
-def addmod(x, y, mod=2 ** 32):
-    """ Modulo adding of two integers
-    """
-    return (x + y) % mod
-
-
 def _shift11(x):
     """ 11-bit cyclic shift
     """
@@ -235,7 +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
 
 
@@ -372,8 +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)