tc/python/lrw.py

   1 ## lrw.py - The LRW cryptographic mode.
   2 ## Copyright (c) 2008 Bjorn Edstrom <be@bjrn.se>
   3 ##
   4 ## Permission is hereby granted, free of charge, to any person
   5 ## obtaining a copy of this software and associated documentation
   6 ## files (the "Software"), to deal in the Software without
   7 ## restriction, including without limitation the rights to use,
   8 ## copy, modify, merge, publish, distribute, sublicense, and/or sell
   9 ## copies of the Software, and to permit persons to whom the
  10 ## Software is furnished to do so, subject to the following
  11 ## conditions:
  12 ##
  13 ## The above copyright notice and this permission notice shall be
  14 ## included in all copies or substantial portions of the Software.
  15 ##
  16 ## THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  17 ## EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
  18 ## OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  19 ## NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
  20 ## HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
  21 ## WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
  22 ## FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
  23 ## OTHER DEALINGS IN THE SOFTWARE.
  24 ## --
  25 ## Changelog
  26 ## Jan 4 2008: Initial version. Plenty of room for improvements.
  27
  28 try:
  29     import psyco
  30     psyco.full()
  31 except ImportError:
  32     pass
  33
  34 from gf2n import *
  35
  36 # C_i = E_K1(P_i ^ (K2 x i)) ^ (K2 x i).
  37 # Note that cipherfunc = E_K1, that is the key should already be set in E.
  38 # lrwkey = K2.
  39 def LRW(cipherfunc, lrwkey, i, block):
  40     """Perform a LRW operation."""
  41
  42     def str2int(str):
  43         N = 0
  44         for c in str:
  45             N <<= 8
  46             N |= ord(c)
  47         return N
  48
  49     def int2str(N):
  50         str = ''
  51         while N:
  52             str = chr(N & 0xff) + str
  53             N >>= 8
  54         return str
  55
  56     def xorstring16(a, b):
  57         new = ''
  58         for p in xrange(16):
  59             new += chr(ord(a[p]) ^ ord(b[p]))
  60         return new
  61
  62     assert len(block) == 16
  63     assert len(lrwkey) == 16
  64     K2 = str2int(lrwkey)
  65     # C_i = E_K1(P_i ^ K2i) ^ K2i
  66     K2i = int2str(gf2pow128mul(K2, i))
  67     K2i = '\x00' * (16 - len(K2i)) + K2i
  68     return xorstring16(K2i, cipherfunc(xorstring16(K2i, block)))
  69
  70 def LRWMany(cipherfunc, lrwkey, i, blocks):
  71     length = len(blocks)
  72     assert length % 16 == 0
  73     data = ''
  74     for b in xrange(length / 16):
  75         data += LRW(cipherfunc, lrwkey, i + b, blocks[0:16])
  76         blocks = blocks[16:]
  77     return data