Use curve's cofactor during VKO calculations

[pygost.git] / pygost / gost3410_vko.py

diff --git a/pygost/gost3410_vko.py b/pygost/gost3410_vko.py
index 35cc06f103293625449dfddbdea59814c37685fe..7bc71113b69e99bcf10dbe2d819d2d8b96361a47 100644 (file)
--- a/pygost/gost3410_vko.py
+++ b/pygost/gost3410_vko.py
@@ -1,11 +1,10 @@
 # coding: utf-8
 # PyGOST -- Pure Python GOST cryptographic functions library
-# Copyright (C) 2015-2016 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
-# the Free Software Foundation, either version 3 of the License, or
-# (at your option) any later version.
+# the Free Software Foundation, version 3 of the License.
 #
 # This program is distributed in the hope that it will be useful,
 # but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ -14,7 +13,7 @@
 #
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
-"""Diffie-Hellman functions, VKO GOST R 34.10-2001/2012
+"""Key agreement functions, VKO GOST R 34.10-2001/2012
 """
 
 from pygost.gost3410 import pub_marshal
@@ -24,15 +23,29 @@ from pygost.gost341194 import GOST341194
 from pygost.utils import bytes2long
 
 
-def vko_34102001(curve, prv, pubkey, ukm):
-    """ Make Diffie-Hellman computation (34.10-2001, 34.11-94)
+def ukm_unmarshal(ukm):
+    """Unmarshal UKM value
+
+    :type ukm: little-endian bytes
+    :rtype: long
+    """
+    return bytes2long(ukm[::-1])
+
+
+def kek(curve, prv, pub, ukm, mode):
+    key = curve.exp(prv, pub[0], pub[1])
+    key = curve.exp(curve.cofactor * ukm, key[0], key[1])
+    return pub_marshal(key, mode)
+
+
+def kek_34102001(curve, prv, pub, ukm):
+    """ Key agreement (34.10-2001, 34.11-94)
 
     :param GOST3410Curve curve: curve to use
     :param long prv: private key
-    :param pubkey: public key
-    :type pubkey: (long, long)
-    :param ukm: UKM value (VKO-factor)
-    :type ukm: bytes, 8 bytes
+    :param pub: public key
+    :type pub: (long, long)
+    :param long ukm: user keying material, VKO-factor
     :returns: Key Encryption Key (shared key)
     :rtype: bytes, 32 bytes
 
@@ -40,40 +53,41 @@ def vko_34102001(curve, prv, pubkey, ukm):
     :rfc:`4357` VKO GOST R 34.10-2001 with little-endian
     hash output.
     """
-    key = curve.exp(prv, pubkey[0], pubkey[1])
-    key = curve.exp(bytes2long(24 * b"\x00" + ukm), key[0], key[1])
-    return GOST341194(pub_marshal(key), "GostR3411_94_CryptoProParamSet").digest()
+    return GOST341194(
+        kek(curve, prv, pub, ukm, mode=2001),
+        sbox="id-GostR3411-94-CryptoProParamSet",
+    ).digest()
 
 
-def vko_34102012256(curve, prv, pubkey, ukm=b"\x00\x00\x00\x00\x00\x00\x00\01"):
-    """ Make Diffie-Hellman computation (34.10-2012, 34.11-2012 256 bit)
+def kek_34102012256(curve, prv, pub, ukm=1, mode=2012):
+    """ Key agreement (34.10-2012, 34.11-2012 256 bit)
 
     :param GOST3410Curve curve: curve to use
     :param long prv: private key
-    :param pubkey: public key
-    :type pubkey: (long, long)
-    :param ukm: UKM value (VKO-factor)
-    :type ukm: bytes, 8 bytes
+    :param pub: public key
+    :type pub: (long, long)
+    :param long ukm: user keying material, VKO-factor
     :returns: Key Encryption Key (shared key)
     :rtype: bytes, 32 bytes
+
+    Shared Key Encryption Key computation is based on
+    :rfc:`7836` VKO GOST R 34.10-2012.
     """
-    key = curve.exp(prv, pubkey[0], pubkey[1])
-    key = curve.exp(bytes2long(ukm[::-1]), key[0], key[1])
-    return GOST34112012256(pub_marshal(key, mode=2012)).digest()
+    return GOST34112012256(kek(curve, prv, pub, ukm, mode=mode)).digest()
 
 
-def vko_34102012512(curve, prv, pubkey, ukm=b"\x00\x00\x00\x00\x00\x00\x00\01"):
-    """ Make Diffie-Hellman computation (34.10-2012, 34.11-2012 512 bit)
+def kek_34102012512(curve, prv, pub, ukm=1):
+    """ Key agreement (34.10-2012, 34.11-2012 512 bit)
 
     :param GOST3410Curve curve: curve to use
     :param long prv: private key
-    :param pubkey: public key
-    :type pubkey: (long, long)
-    :param ukm: UKM value (VKO-factor)
-    :type ukm: bytes, 8 bytes
+    :param pub: public key
+    :type pub: (long, long)
+    :param long ukm: user keying material, VKO-factor
     :returns: Key Encryption Key (shared key)
     :rtype: bytes, 32 bytes
+
+    Shared Key Encryption Key computation is based on
+    :rfc:`7836` VKO GOST R 34.10-2012.
     """
-    key = curve.exp(prv, pubkey[0], pubkey[1])
-    key = curve.exp(bytes2long(ukm[::-1]), key[0], key[1])
-    return GOST34112012512(pub_marshal(key, mode=2012)).digest()
+    return GOST34112012512(kek(curve, prv, pub, ukm, mode=2012)).digest()