arcfour.c 1.92 KB
Newer Older
Niels Möller's avatar
Niels Möller committed
1
/* arcfour.c
Niels Möller's avatar
Niels Möller committed
2
 *
Niels Möller's avatar
Niels Möller committed
3 4 5 6 7
 * This implements the Arcfour stream cipher with 128 bit keys. 
 *
 * The Arcfour cipher is believed to be compatible with the RC4 cipher. 
 * RC4 is a registered trademark of RSA Data Security Inc.
 *   
Niels Möller's avatar
Niels Möller committed
8 9
 */

Niels Möller's avatar
Niels Möller committed
10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28
/* lsh, an implementation of the ssh protocol
 *
 * Copyright (C) 1998 Niels Mller
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation; either version 2 of the
 * License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

Niels Möller's avatar
src/  
Niels Möller committed
29
#include "arcfour.h"
Niels Möller's avatar
Niels Möller committed
30 31 32 33 34 35 36

#ifdef RCSID
RCSID("$Id$");
#endif

#define SWAP(a,b) do { int _t = a; a = b; b = _t; } while(0)

Niels Möller's avatar
Niels Möller committed
37
void arcfour_set_key(struct arcfour_ctx *ctx, const UINT8 *key, UINT32 len)
Niels Möller's avatar
Niels Möller committed
38
{
39
  register UINT8 j; /* Depends on the eight-bitness of these variables. */
Niels Möller's avatar
Niels Möller committed
40
  unsigned i;
41
  UINT32 k;
Niels Möller's avatar
Niels Möller committed
42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57

  /* Initialize context */
  i = 0;
  do ctx->S[i] = i; while (++i < 256);

  /* Expand key */
  i = j = k = 0;
  do {
    j += ctx->S[i] + key[k];
    SWAP(ctx->S[i], ctx->S[j]);
    k = (k+1) % len; /* Repeat key if needed */
  } while(++i < 256);
  
  ctx->i = ctx->j = 0;
}

Niels Möller's avatar
Niels Möller committed
58 59
void arcfour_crypt(struct arcfour_ctx *ctx, UINT8 *dest,
		   const UINT8 *src, UINT32 len)
Niels Möller's avatar
Niels Möller committed
60
{
61
  register UINT8 i, j;
Niels Möller's avatar
Niels Möller committed
62 63 64 65

  i = ctx->i; j = ctx->j;
  while(len--)
    {
66 67
      i++; i &= 0xff;
      j += ctx->S[i]; j &= 0xff;
Niels Möller's avatar
Niels Möller committed
68 69 70 71 72
      SWAP(ctx->S[i], ctx->S[j]);
      *dest++ = *src++ ^ ctx->S[ (ctx->S[i] + ctx->S[j]) & 0xff ];
    }
  ctx->i = i; ctx->j = j;
}