/* arcfour.c */
/*
 This file is part of the AVR-Crypto-Lib.
 Copyright (C) 2006-2015 Daniel Otte (bg@nerilex.org)

 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 3 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, see <http://www.gnu.org/licenses/>.
 */
/*
 * File:        arcfour.c
 * Author:      Daniel Otte
 * email:       bg@nerilex.org
 * Date:        2006-06-07
 * License:     GPLv3 or later
 * Description: Implementation of the ARCFOUR (RC4 compatible) stream cipher algorithm.
 *
 */

#include <stdint.h>
#include "arcfour.h"

/*
 * length is length of key in bytes!
 */

void arcfour_init(const void *key, uint16_t length_b, arcfour_ctx_t *ctx)
{
    uint8_t t;
    const uint8_t length_B = length_b / 8;
    uint8_t nidx = length_B;
    uint8_t x = 0, y = 0;
    const uint8_t *kptr = (const uint8_t*) key;
    do {
        ctx->s[x] = x;
    } while ((uint8_t) ++x);

    do {
        y += ctx->s[x] + *kptr++;
        if (!--nidx) {
            kptr = (const uint8_t*) key;
            nidx = length_B;
        }
        y &= 0xff;
        /* ctx->s[y] <--> ctx->s[x] */
        t = ctx->s[y];
        ctx->s[y] = ctx->s[x];
        ctx->s[x] = t;
    } while ((uint8_t) ++x);

    ctx->i = ctx->j = 0;
}

uint8_t arcfour_gen(arcfour_ctx_t *ctx)
{
    uint8_t t;
    ctx->i++;
    ctx->j += ctx->s[ctx->i];
    /* ctx->s[i] <--> ctx->s[j] */
    t = ctx->s[ctx->j];
    ctx->s[ctx->j] = ctx->s[ctx->i];
    ctx->s[ctx->i] = t;
    return ctx->s[(ctx->s[ctx->j] + ctx->s[ctx->i]) & 0xff];
}