lib/arcfour.c

   1 /* arcfour.c --- The arcfour stream cipher
   2  * Copyright (C) 2000-2003, 2005-2006, 2009-2011 Free Software Foundation, Inc.
   3  *
   4  * This file is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License as published
   6  * by the Free Software Foundation; either version 2, or (at your
   7  * option) any later version.
   8  *
   9  * This file is distributed in the hope that it will be useful, but
  10  * WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12  * General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with this file; if not, write to the Free Software
  16  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
  17  * 02110-1301, USA.
  18  *
  19  */
  20
  21 /* Code from Libgcrypt adapted for gnulib by Simon Josefsson. */
  22
  23 /*
  24  * For a description of the algorithm, see:
  25  *   Bruce Schneier: Applied Cryptography. John Wiley & Sons, 1996.
  26  *   ISBN 0-471-11709-9. Pages 397 ff.
  27  */
  28
  29 #include <config.h>
  30
  31 #include "arcfour.h"
  32
  33 void
  34 arcfour_stream (arcfour_context * context, const char *inbuf, char *outbuf,
  35                 size_t length)
  36 {
  37   uint8_t i = context->idx_i;
  38   uint8_t j = context->idx_j;
  39   char *sbox = context->sbox;
  40
  41   for (; length > 0; length--)
  42     {
  43       char t;
  44
  45       i++;
  46       j += sbox[i];
  47       t = sbox[i];
  48       sbox[i] = sbox[j];
  49       sbox[j] = t;
  50       *outbuf++ = (*inbuf++
  51                    ^ sbox[(0U + sbox[i] + sbox[j]) % ARCFOUR_SBOX_SIZE]);
  52     }
  53
  54   context->idx_i = i;
  55   context->idx_j = j;
  56 }
  57
  58 void
  59 arcfour_setkey (arcfour_context * context, const char *key, size_t keylen)
  60 {
  61   size_t i, j, k;
  62   char *sbox = context->sbox;
  63
  64   context->idx_i = context->idx_j = 0;
  65   for (i = 0; i < ARCFOUR_SBOX_SIZE; i++)
  66     sbox[i] = i;
  67   for (i = j = k = 0; i < ARCFOUR_SBOX_SIZE; i++)
  68     {
  69       char t;
  70       j = (j + sbox[i] + key[k]) % ARCFOUR_SBOX_SIZE;
  71       t = sbox[i];
  72       sbox[i] = sbox[j];
  73       sbox[j] = t;
  74       if (++k == keylen)
  75         k = 0;
  76     }
  77 }