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/*

 * rc4.c

 *

 * Copyright (c) 1996-2000 Whistle Communications, Inc.

 * All rights reserved.

 *

 * Subject to the following obligations and disclaimer of warranty, use and

 * redistribution of this software, in source or object code forms, with or

 * without modifications are expressly permitted by Whistle Communications;

 * provided, however, that:

 * 1. Any and all reproductions of the source or object code must include the

 *    copyright notice above and the following disclaimer of warranties; and

 * 2. No rights are granted, in any manner or form, to use Whistle

 *    Communications, Inc. trademarks, including the mark "WHISTLE

 *    COMMUNICATIONS" on advertising, endorsements, or otherwise except as

 *    such appears in the above copyright notice or in the software.

 *

 * THIS SOFTWARE IS BEING PROVIDED BY WHISTLE COMMUNICATIONS "AS IS", AND

 * TO THE MAXIMUM EXTENT PERMITTED BY LAW, WHISTLE COMMUNICATIONS MAKES NO

 * REPRESENTATIONS OR WARRANTIES, EXPRESS OR IMPLIED, REGARDING THIS SOFTWARE,

 * INCLUDING WITHOUT LIMITATION, ANY AND ALL IMPLIED WARRANTIES OF

 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, OR NON-INFRINGEMENT.

 * WHISTLE COMMUNICATIONS DOES NOT WARRANT, GUARANTEE, OR MAKE ANY

 * REPRESENTATIONS REGARDING THE USE OF, OR THE RESULTS OF THE USE OF THIS

 * SOFTWARE IN TERMS OF ITS CORRECTNESS, ACCURACY, RELIABILITY OR OTHERWISE.

 * IN NO EVENT SHALL WHISTLE COMMUNICATIONS BE LIABLE FOR ANY DAMAGES

 * RESULTING FROM OR ARISING OUT OF ANY USE OF THIS SOFTWARE, INCLUDING

 * WITHOUT LIMITATION, ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY,

 * PUNITIVE, OR CONSEQUENTIAL DAMAGES, PROCUREMENT OF SUBSTITUTE GOODS OR

 * SERVICES, LOSS OF USE, DATA OR PROFITS, HOWEVER CAUSED AND UNDER 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 WHISTLE COMMUNICATIONS IS ADVISED OF THE POSSIBILITY

 * OF SUCH DAMAGE.

 */

#include <rc4.h>

void swap_bytes(uint8_t *a, uint8_t *b)

{

  /*

  _asm

    ld    d,4(ix)

    ld    e,5(ix)

    ld    h,6(ix)

    ld    l,7(ix)

    ld    a, (de)

    ld    b, a

    ld    a, (hl)

    ld    (de), a

    ld    (hl), b

  _endasm;

  */

        uint8_t temp;

        temp = *a;

        *a = *b;

        *b = temp;

}

/*

 * Initialize an RC4 state buffer using the supplied key,

 * which can have arbitrary length.

 */

void rc4_init(struct rc4_state *const state, const uint8_t *key, int keylen)

{

        uint8_t j;

        int i;

        /* Initialize state with identity permutation */

#ifndef ORIGINAL_C

    _asm

    ld    d, 4(ix)

    ld    e, 5(ix)

    ld    b, #255

state_init:

    ld    h, #0

    ld    l, b

    add   hl, de

    ld    (hl), b

    djnz  state_init

    ex    de, hl

    ld    (hl), #0

    ex    de, hl

    ld    l, #0

    ld    h, #1

    add   hl, de

    ld    (hl), #0

    inc   hl

    ld    (hl), #0

    _endasm;

#else

        for (i = 0; i < 256; i++)

                state->perm[i] = (uint8_t)i;

        state->index1 = 0;

        state->index2 = 0;

#endif

        /* Randomize the permutation using key data */

        for (j = i = 0; i < 256; i++) {

          uint8_t tmp;

          j += state->perm[i] + key[i % keylen];

          tmp = state->perm[i];

          state->perm[i] = state->perm[j];

          state->perm[j] = tmp;

          //swap_bytes(&state->perm[i], &state->perm[j]);

        }

}

/*

 * Encrypt some data using the supplied RC4 state buffer.

 * The input and output buffers may be the same buffer.

 * Since RC4 is a stream cypher, this function is used

 * for both encryption and decryption.

 */

void rc4_crypt(struct rc4_state *const state,

        const uint8_t *inbuf, uint8_t *outbuf, int buflen)

{

        int i;

        uint8_t j;

        for (i = 0; i < buflen; i++) {

                /* Update modification indicies */

                state->index1++;

                state->index2 += state->perm[state->index1];

                /* Modify permutation */

                swap_bytes(&state->perm[state->index1],

                    &state->perm[state->index2]);

                /* Encrypt/decrypt next byte */

                j = state->perm[state->index1] + state->perm[state->index2];

                outbuf[i] = inbuf[i] ^ state->perm[j];

        }

}