src/lib/crypto/rc4.c

   1 /*
   2  * Copyright (c) 2007, Cameron Rich
   3  *
   4  * All rights reserved.
   5  *
   6  * Redistribution and use in source and binary forms, with or without
   7  * modification, are permitted provided that the following conditions are met:
   8  *
   9  * * Redistributions of source code must retain the above copyright notice,
  10  *   this list of conditions and the following disclaimer.
  11  * * Redistributions in binary form must reproduce the above copyright notice,
  12  *   this list of conditions and the following disclaimer in the documentation
  13  *   and/or other materials provided with the distribution.
  14  * * Neither the name of the axTLS project nor the names of its contributors
  15  *   may be used to endorse or promote products derived from this software
  16  *   without specific prior written permission.
  17  *
  18  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  19  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  20  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  21  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
  22  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  23  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  24  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
  25  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
  26  * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
  27  * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
  28  * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  29  */
  30
  31 /**
  32  * An implementation of the RC4/ARC4 algorithm.
  33  * Originally written by Christophe Devine.
  34  */
  35
  36 #include <string.h>
  37 #include "os_port.h"
  38 #include "crypto.h"
  39
  40 /**
  41  * Get ready for an encrypt/decrypt operation
  42  */
  43 void RC4_setup(RC4_CTX *ctx, const uint8_t *key, int length)
  44 {
  45     int i, j = 0, k = 0, a;
  46     uint8_t *m;
  47
  48     ctx->x = 0;
  49     ctx->y = 0;
  50     m = ctx->m;
  51
  52     for (i = 0; i < 256; i++)
  53         m[i] = i;
  54
  55     for (i = 0; i < 256; i++)
  56     {
  57         a = m[i];
  58         j = (uint8_t)(j + a + key[k]);
  59         m[i] = m[j];
  60         m[j] = a;
  61
  62         if (++k >= length)
  63             k = 0;
  64     }
  65 }
  66
  67 /**
  68  * Perform the encrypt/decrypt operation (can use it for either since
  69  * this is a stream cipher).
  70  * NOTE: *msg and *out must be the same pointer (performance tweak)
  71  */
  72 void RC4_crypt(RC4_CTX *ctx, const uint8_t *msg, uint8_t *out, int length)
  73 {
  74     int i;
  75     uint8_t *m, x, y, a, b;
  76
  77     x = ctx->x;
  78     y = ctx->y;
  79     m = ctx->m;
  80
  81     for (i = 0; i < length; i++)
  82     {
  83         a = m[++x];
  84         y += a;
  85         m[x] = b = m[y];
  86         m[y] = a;
  87         out[i] ^= m[(uint8_t)(a + b)];
  88     }
  89
  90     ctx->x = x;
  91     ctx->y = y;
  92 }