cryb-to/lib/cipher/rc4.c

/*-
 * Copyright (c) 2015 Dag-Erling Smørgrav
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. 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.
 * 3. The name of the author may not be used to endorse or promote
 *    products derived from this software without specific prior written
 *    permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR 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 AUTHOR 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.
 */

#include "cryb/impl.h"

#include <stdint.h>
#include <string.h>

#include <cryb/bitwise.h>
#include <cryb/endian.h>

#include <cryb/rc4.h>

void
rc4_init(rc4_ctx *ctx, cipher_mode mode, const uint8_t *key, size_t keylen)
{
	unsigned int i, j;
	uint8_t t;

	(void)mode;
	memset(ctx, 0, sizeof *ctx);
	for (i = 0; i < 256; ++i)
		ctx->s[i] = i;
	for (i = j = 0; i < 256; ++i) {
		j = (j + ctx->s[i] + key[i % keylen]) % 256;
		t = ctx->s[i];
		ctx->s[i] = ctx->s[j];
		ctx->s[j] = t;
	}
}

void
rc4_update(rc4_ctx *ctx, const void *in, size_t len, void *out)
{
	const uint8_t *is = in;
	uint8_t t, k, *os = out;
	unsigned int i;

	for (i = 0; i < len; ++i) {
		ctx->i = ctx->i + 1;
		ctx->j = ctx->j + ctx->s[ctx->i];
		t = ctx->s[ctx->i];
		ctx->s[ctx->i] = ctx->s[ctx->j];
		ctx->s[ctx->j] = t;
		t = ctx->s[ctx->i] + ctx->s[ctx->j];
		k = ctx->s[t];
		*os++ = *is++ ^ k;
	}
}

void
rc4_finish(rc4_ctx *ctx)
{

	memset(ctx, 0, sizeof *ctx);
}

cipher_algorithm rc4_cipher = {
	.name			 = "rc4",
	.contextlen		 = sizeof(rc4_ctx),
	.blocklen		 = 1,
	.keylen			 = 0,
	.init			 = (cipher_init_func)rc4_init,
	.update			 = (cipher_update_func)rc4_update,
	.finish			 = (cipher_finish_func)rc4_finish,
};