release/src/router/nettle/arcfour.c

   1 /* arcfour.c
   2  *
   3  * The arcfour/rc4 stream cipher.
   4  */
   5
   6 /* nettle, low-level cryptographics library
   7  *
   8  * Copyright (C) 2001 Niels Möller
   9  *
  10  * The nettle library is free software; you can redistribute it and/or modify
  11  * it under the terms of the GNU Lesser General Public License as published by
  12  * the Free Software Foundation; either version 2.1 of the License, or (at your
  13  * option) any later version.
  14  *
  15  * The nettle library is distributed in the hope that it will be useful, but
  16  * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  17  * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
  18  * License for more details.
  19  *
  20  * You should have received a copy of the GNU Lesser General Public License
  21  * along with the nettle library; see the file COPYING.LIB.  If not, write to
  22  * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
  23  * MA 02111-1301, USA.
  24  */
  25
  26 #if HAVE_CONFIG_H
  27 # include "config.h"
  28 #endif
  29
  30 #include <assert.h>
  31
  32 #include "arcfour.h"
  33
  34 #define SWAP(a,b) do { int _t = a; a = b; b = _t; } while(0)
  35
  36 void
  37 arcfour_set_key(struct arcfour_ctx *ctx,
  38                 unsigned length, const uint8_t *key)
  39 {
  40   unsigned i, j, k;
  41
  42   assert(length >= ARCFOUR_MIN_KEY_SIZE);
  43   assert(length <= ARCFOUR_MAX_KEY_SIZE);
  44
  45   /* Initialize context */
  46   for (i = 0; i<256; i++)
  47     ctx->S[i] = i;
  48
  49   for (i = j = k = 0; i<256; i++)
  50     {
  51       j += ctx->S[i] + key[k]; j &= 0xff;
  52       SWAP(ctx->S[i], ctx->S[j]);
  53       /* Repeat key as needed */
  54       k = (k + 1) % length;
  55     }
  56   ctx->i = ctx->j = 0;
  57 }
  58