arc4.c

/*
 *  An implementation of the ARCFOUR algorithm
 *
 *  Based on XySSL: Copyright (C) 2006-2008  Christophe Devine
 *
 *  Copyright (C) 2009  Paul Bakker <polarssl_maintainer at polarssl dot org>
 *
 *  All rights reserved.
 *
 *  Redistribution and use in source and binary forms, with or without
 *  modification, are permitted provided that the following conditions
 *  are met:
 *  
 *    * Redistributions of source code must retain the above copyright
 *      notice, this list of conditions and the following disclaimer.
 *    * Redistributions in binary form must reproduce the above copyright
 *      notice, this list of conditions and the following disclaimer in the
 *      documentation and/or other materials provided with the distribution.
 *    * Neither the names of PolarSSL or XySSL nor the names of its contributors
 *      may be used to endorse or promote products derived from this software
 *      without specific prior written permission.
 *  
 *  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 *  "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 *  LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 *  FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 *  OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 *  SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
 *  TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 *  PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 *  LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 *  NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 *  SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
/*
 *  The ARCFOUR algorithm was publicly disclosed on 94/09.
 *
 *  http://groups.google.com/group/sci.crypt/msg/10a300c9d21afca0
 */

#include "netif/ppp/ppp_opts.h"
#if PPP_SUPPORT && LWIP_INCLUDED_POLARSSL_ARC4

#include "netif/ppp/polarssl/arc4.h"
/*
 * ARC4 key schedule
 */
void arc4_setup( arc4_context *ctx, unsigned char *key, int keylen )
{
    int i, j, k, a;
    unsigned char *m;

    ctx->x = 0;
    ctx->y = 0;
    m = ctx->m;

    for( i = 0; i < 256; i++ )
        m[i] = (unsigned char) i;

    j = k = 0;

    for( i = 0; i < 256; i++, k++ )
    {
        if( k >= keylen ) k = 0;

        a = m[i];
        j = ( j + a + key[k] ) & 0xFF;
        m[i] = m[j];
        m[j] = (unsigned char) a;
    }
}

/*
 * ARC4 cipher function
 */
void arc4_crypt( arc4_context *ctx, unsigned char *buf, int buflen )
{
    int i, x, y, a, b;
    unsigned char *m;

    x = ctx->x;
    y = ctx->y;
    m = ctx->m;

    for( i = 0; i < buflen; i++ )
    {
        x = ( x + 1 ) & 0xFF; a = m[x];
        y = ( y + a ) & 0xFF; b = m[y];

        m[x] = (unsigned char) b;
        m[y] = (unsigned char) a;

        buf[i] = (unsigned char)
            ( buf[i] ^ m[(unsigned char)( a + b )] );
    }

    ctx->x = x;
    ctx->y = y;
}

#endif /* PPP_SUPPORT && LWIP_INCLUDED_POLARSSL_DES */