reactos/lib/cryptlib/rc4.c

   1 /*
   2  *  Copyright 2006 Mike McCormack
   3  *
   4  *  based on arc4.cpp - written and placed in the public domain by Wei Dai
   5  *
   6  *  This library is free software; you can redistribute it and/or
   7  *  modify it under the terms of the GNU Lesser General Public
   8  *  License as published by the Free Software Foundation; either
   9  *  version 2.1 of the License, or (at your option) any later version.
  10  *
  11  *  This library is distributed in the hope that it will be useful,
  12  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14  *  Lesser General Public License for more details.
  15  *
  16  *  You should have received a copy of the GNU Lesser General Public
  17  *  License along with this library; if not, write to the Free Software
  18  *  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
  19  */
  20
  21 /* http://cryptopp.sourceforge.net/docs/ref521/arc4_8cpp-source.html */
  22
  23 #include "rc4.h"
  24
  25 void rc4_init(RC4_CONTEXT *a4i, const unsigned char *key, unsigned int keyLen)
  26 {
  27     unsigned int keyIndex = 0, stateIndex = 0;
  28     unsigned int i, a;
  29
  30     a4i->x = a4i->y = 0;
  31
  32     for (i=0; i<256; i++)
  33         a4i->state[i] = i;
  34
  35     for (i=0; i<256; i++)
  36     {
  37         a = a4i->state[i];
  38         stateIndex += key[keyIndex] + a;
  39         stateIndex &= 0xff;
  40         a4i->state[i] = a4i->state[stateIndex];
  41         a4i->state[stateIndex] = a;
  42         if (++keyIndex >= keyLen)
  43             keyIndex = 0;
  44     }
  45 }
  46
  47 void rc4_crypt(RC4_CONTEXT *a4i, unsigned char *inoutString, unsigned int length)
  48 {
  49     unsigned char *const s=a4i->state;
  50     unsigned int x = a4i->x;
  51     unsigned int y = a4i->y;
  52     unsigned int a, b;
  53
  54     while(length--)
  55     {
  56         x = (x+1) & 0xff;
  57         a = s[x];
  58         y = (y+a) & 0xff;
  59         b = s[y];
  60         s[x] = b;
  61         s[y] = a;
  62         *inoutString++ ^= s[(a+b) & 0xff];
  63     }
  64
  65     a4i->x = x;
  66     a4i->y = y;
  67 }