/*
* 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
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* (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"

static __inline void swap_bytes(uint8_t *a, uint8_t *b) {
  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 */
  for (i = 0; i < 256; i++) state->perm[i] = (uint8_t)i;
  state->index1 = 0;
  state->index2 = 0;

  /* Randomize the permutation using key data */
  for (j = i = 0; i < 256; i++) {
    j += state->perm[i] + key[i % keylen];
    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];
  }
}