* Fix a typo in the dpkg changelog.
[deb_shairplay.git] / 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 }