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/* arcfour.c
*
* The arcfour/rc4 stream cipher.
*/
/* nettle, low-level cryptographics library
*
* Copyright (C) 2001 Niels Möller
*
* The nettle library is free software; you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as published by
* the Free Software Foundation; either version 2.1 of the License, or (at your
* option) any later version.
*
* The nettle library 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 Lesser General Public
* License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with the nettle library; see the file COPYING.LIB. If not, write to
* the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
* MA 02111-1307, USA.
*/
#if HAVE_CONFIG_H
# include "config.h"
#endif
#include <assert.h>
#include "arcfour.h"
#define SWAP(a,b) do { int _t = a; a = b; b = _t; } while(0)
void
arcfour_set_key(struct arcfour_ctx *ctx,
unsigned length, const uint8_t *key)
{
unsigned i, j, k;
assert(length >= ARCFOUR_MIN_KEY_SIZE);
assert(length <= ARCFOUR_MAX_KEY_SIZE);
/* Initialize context */
for (i = 0; i<256; i++)
ctx->S[i] = i;
for (i = j = k = 0; i<256; i++)
{
j += ctx->S[i] + key[k]; j &= 0xff;
SWAP(ctx->S[i], ctx->S[j]);
/* Repeat key as needed */
k = (k + 1) % length;
}
ctx->i = ctx->j = 0;
}
void
arcfour_stream(struct arcfour_ctx *ctx,
unsigned length, uint8_t *dst)
{
register uint8_t i, j;
register int si, sj;
i = ctx->i; j = ctx->j;
while(length--)
{
i++; i &= 0xff;
si = ctx->S[i];
j += si; j &= 0xff;
sj = ctx->S[i] = ctx->S[j];
ctx->S[j] = si;
*dst++ = ctx->S[ (si + sj) & 0xff ];
}
ctx->i = i; ctx->j = j;
}
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