lgl/arcfour.c

   1 /* arcfour.c --- The arcfour stream cipher
   2  * Copyright (C) 2000, 2001, 2002, 2003, 2005, 2006 Free Software
   3  * Foundation, Inc.
   4  *
   5  * This file is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU Lesser General Public License as published
   7  * by the Free Software Foundation; either version 2.1, or (at your
   8  * option) any later version.
   9  *
  10  * This file is distributed in the hope that it will be useful, but
  11  * WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13  * General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU Lesser General Public License
  16  * along with this file; if not, write to the Free Software
  17  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
  18  * 02110-1301, USA.
  19  *
  20  */
  21
  22 /* Code from Libgcrypt adapted for gnulib by Simon Josefsson. */
  23
  24 /*
  25  * For a description of the algorithm, see:
  26  *   Bruce Schneier: Applied Cryptography. John Wiley & Sons, 1996.
  27  *   ISBN 0-471-11709-9. Pages 397 ff.
  28  */
  29
  30 #include <config.h>
  31
  32 #include "arcfour.h"
  33
  34 void
  35 arcfour_stream (arcfour_context * context, const char *inbuf, char *outbuf,
  36                 size_t length)
  37 {
  38   uint8_t i = context->idx_i;
  39   uint8_t j = context->idx_j;
  40   char *sbox = context->sbox;
  41
  42   for (; length > 0; length--)
  43     {
  44       char t;
  45
  46       i++;
  47       j += sbox[i];
  48       t = sbox[i];
  49       sbox[i] = sbox[j];
  50       sbox[j] = t;
  51       *outbuf++ = (*inbuf++
  52                    ^ sbox[(0U + sbox[i] + sbox[j]) % ARCFOUR_SBOX_SIZE]);
  53     }
  54
  55   context->idx_i = i;
  56   context->idx_j = j;
  57 }
  58
  59 void
  60 arcfour_setkey (arcfour_context * context, const char *key, size_t keylen)
  61 {
  62   size_t i, j, k;
  63   char *sbox = context->sbox;
  64
  65   context->idx_i = context->idx_j = 0;
  66   for (i = 0; i < ARCFOUR_SBOX_SIZE; i++)
  67     sbox[i] = i;
  68   for (i = j = k = 0; i < ARCFOUR_SBOX_SIZE; i++)
  69     {
  70       char t;
  71       j = (j + sbox[i] + key[k]) % ARCFOUR_SBOX_SIZE;
  72       t = sbox[i];
  73       sbox[i] = sbox[j];
  74       sbox[j] = t;
  75       if (++k == keylen)
  76         k = 0;
  77     }
  78 }