rc4.c

00001 /*
00002  * Copyright (c) 2007, Cameron Rich
00003  * 
00004  * All rights reserved.
00005  * 
00006  * Redistribution and use in source and binary forms, with or without 
00007  * modification, are permitted provided that the following conditions are met:
00008  *
00009  * * Redistributions of source code must retain the above copyright notice, 
00010  *   this list of conditions and the following disclaimer.
00011  * * Redistributions in binary form must reproduce the above copyright notice, 
00012  *   this list of conditions and the following disclaimer in the documentation 
00013  *   and/or other materials provided with the distribution.
00014  * * Neither the name of the axTLS project nor the names of its contributors 
00015  *   may be used to endorse or promote products derived from this software 
00016  *   without specific prior written permission.
00017  *
00018  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
00019  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
00020  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
00021  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
00022  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
00023  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
00024  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
00025  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
00026  * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
00027  * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
00028  * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
00029  */
00030 
00031 /**
00032  * An implementation of the RC4/ARC4 algorithm.
00033  * Originally written by Christophe Devine.
00034  */
00035 
00036 #include <string.h>
00037 #include "os_port.h"
00038 #include "crypto.h "
00039 
00040 /**
00041  * Get ready for an encrypt/decrypt operation
00042  */
00043 void RC4_setup(RC4_CTX *ctx, const uint8_t *key, int length)
00044 {
00045     int i, j = 0, k = 0, a;
00046     uint8_t *m;
00047 
00048     ctx->x = 0;
00049     ctx->y = 0;
00050     m = ctx->m;
00051 
00052     for (i = 0; i < 256; i++)
00053         m[i] = i;
00054 
00055     for (i = 0; i < 256; i++)
00056     {
00057         a = m[i];
00058         j = (uint8_t)(j + a + key[k]);
00059         m[i] = m[j]; 
00060         m[j] = a;
00061 
00062         if (++k >= length) 
00063             k = 0;
00064     }
00065 }
00066 
00067 /**
00068  * Perform the encrypt/decrypt operation (can use it for either since
00069  * this is a stream cipher).
00070  * NOTE: *msg and *out must be the same pointer (performance tweak)
00071  */
00072 void RC4_crypt(RC4_CTX *ctx, const uint8_t *msg, uint8_t *out, int length)
00073 { 
00074     int i;
00075     uint8_t *m, x, y, a, b;
00076 
00077     x = ctx->x;
00078     y = ctx->y;
00079     m = ctx->m;
00080 
00081     for (i = 0; i < length; i++)
00082     {
00083         a = m[++x];
00084         y += a;
00085         m[x] = b = m[y];
00086         m[y] = a;
00087         out[i] ^= m[(uint8_t)(a + b)];
00088     }
00089 
00090     ctx->x = x;
00091     ctx->y = y;
00092 }