dlls/rsaenh/rc4.c

   1 /*
   2  * dlls/rsaenh/rc4.c
   3  * RC4 functions
   4  *
   5  * Copyright 2004 Michael Jung
   6  * Based on public domain code by Tom St Denis (tomstdenis@iahu.ca)
   7  *
   8  * This library is free software; you can redistribute it and/or
   9  * modify it under the terms of the GNU Lesser General Public
  10  * License as published by the Free Software Foundation; either
  11  * version 2.1 of the License, or (at your option) any later version.
  12  *
  13  * This library is distributed in the hope that it will be useful,
  14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  16  * Lesser General Public License for more details.
  17  *
  18  * You should have received a copy of the GNU Lesser General Public
  19  * License along with this library; if not, write to the Free Software
  20  * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
  21  */
  22
  23 /*
  24  * This file contains code from the LibTomCrypt cryptographic
  25  * library written by Tom St Denis (tomstdenis@iahu.ca). LibTomCrypt
  26  * is in the public domain. The code in this file is tailored to
  27  * special requirements. Take a look at http://libtomcrypt.org for the
  28  * original version.
  29  */
  30
  31 #include "tomcrypt.h"
  32
  33 int rc4_start(prng_state *prng)
  34 {
  35     /* set keysize to zero */
  36     prng->rc4.x = 0;
  37
  38     return CRYPT_OK;
  39 }
  40
  41 int rc4_add_entropy(const unsigned char *buf, unsigned long len, prng_state *prng)
  42 {
  43     /* trim as required */
  44     if (prng->rc4.x + len > 256) {
  45        if (prng->rc4.x == 256) {
  46           /* I can't possibly accept another byte, ok maybe a mint wafer... */
  47           return CRYPT_OK;
  48        } else {
  49           /* only accept part of it */
  50           len = 256 - prng->rc4.x;
  51        }
  52     }
  53
  54     while (len--) {
  55        prng->rc4.buf[prng->rc4.x++] = *buf++;
  56     }
  57
  58     return CRYPT_OK;
  59 }
  60
  61 int rc4_ready(prng_state *prng)
  62 {
  63     unsigned char key[256], tmp, *s;
  64     int keylen, x, y, j;
  65
  66     /* extract the key */
  67     s = prng->rc4.buf;
  68     memcpy(key, s, 256);
  69     keylen = prng->rc4.x;
  70
  71     /* make RC4 perm and shuffle */
  72     for (x = 0; x < 256; x++) {
  73         s[x] = x;
  74     }
  75
  76     for (j = x = y = 0; x < 256; x++) {
  77         y = (y + prng->rc4.buf[x] + key[j++]) & 255;
  78         if (j == keylen) {
  79            j = 0;
  80         }
  81         tmp = s[x]; s[x] = s[y]; s[y] = tmp;
  82     }
  83     prng->rc4.x = 0;
  84     prng->rc4.y = 0;
  85
  86     return CRYPT_OK;
  87 }
  88
  89 unsigned long rc4_read(unsigned char *buf, unsigned long len, prng_state *prng)
  90 {
  91    unsigned char x, y, *s, tmp;
  92    unsigned long n;
  93
  94    n = len;
  95    x = prng->rc4.x;
  96    y = prng->rc4.y;
  97    s = prng->rc4.buf;
  98    while (len--) {
  99       x = (x + 1) & 255;
 100       y = (y + s[x]) & 255;
 101       tmp = s[x]; s[x] = s[y]; s[y] = tmp;
 102       tmp = (s[x] + s[y]) & 255;
 103       *buf++ ^= s[tmp];
 104    }
 105    prng->rc4.x = x;
 106    prng->rc4.y = y;
 107    return n;
 108 }