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Annotation of embedaddon/axTLS/crypto/rc4.c, revision 1.1.1.1

1.1       misho       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: }