* Fix a typo in the dpkg changelog.

[deb_shairplay.git] / src / lib / crypto / rc4.c

/*
 * Copyright (c) 2007, Cameron Rich
 * 
 * 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 name of the axTLS project 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.
 */

/**
 * An implementation of the RC4/ARC4 algorithm.
 * Originally written by Christophe Devine.
 */

#include <string.h>
#include "os_port.h"
#include "crypto.h"

/**
 * Get ready for an encrypt/decrypt operation
 */
void RC4_setup(RC4_CTX *ctx, const uint8_t *key, int length)
{
    int i, j = 0, k = 0, a;
    uint8_t *m;

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

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

    for (i = 0; i < 256; i++)
    {
        a = m[i];
        j = (uint8_t)(j + a + key[k]);
        m[i] = m[j]; 
        m[j] = a;

        if (++k >= length) 
            k = 0;
    }
}

/**
 * Perform the encrypt/decrypt operation (can use it for either since
 * this is a stream cipher).
 * NOTE: *msg and *out must be the same pointer (performance tweak)
 */
void RC4_crypt(RC4_CTX *ctx, const uint8_t *msg, uint8_t *out, int length)
{ 
    int i;
    uint8_t *m, x, y, a, b;

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

    for (i = 0; i < length; i++)
    {
        a = m[++x];
        y += a;
        m[x] = b = m[y];
        m[y] = a;
        out[i] ^= m[(uint8_t)(a + b)];
    }

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