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/* arcfour.c
*
* 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.
*
*/
/* lsh, an implementation of the ssh protocol
*
* Copyright (C) 1998 Niels Möller
*
* 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
*/
#include "arcfour.h"
#ifdef RCSID
RCSID("$Id$");
#endif
#define SWAP(a,b) do { int _t = a; a = b; b = _t; } while(0)
void arcfour_set_key(struct arcfour_ctx *ctx, const UINT8 *key, UINT32 len)
{
register UINT8 j; /* Depends on the eight-bitness of these variables. */
unsigned i;
UINT32 k;
/* 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;
}
void arcfour_crypt(struct arcfour_ctx *ctx, UINT8 *dest,
const UINT8 *src, UINT32 len)
{
register UINT8 i, j;
i = ctx->i; j = ctx->j;
while(len--)
{
i++; i &= 0xff;
j += ctx->S[i]; j &= 0xff;
SWAP(ctx->S[i], ctx->S[j]);
*dest++ = *src++ ^ ctx->S[ (ctx->S[i] + ctx->S[j]) & 0xff ];
}
ctx->i = i; ctx->j = j;
}
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