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Shun time(), since on Linux it is not monotonic with gettimeofday().
[disorder] / lib / arcfour.c
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1/* arcfour.c --- The arcfour stream cipher
2 * Copyright (C) 2000, 2001, 2002, 2003, 2005, 2006 Free Software
3 * Foundation, Inc.
4 *
5 * This file is free software; you can redistribute it and/or modify
6 * it under the terms of the GNU General Public License as published
7 * by the Free Software Foundation; either version 2, or (at your
8 * option) any later version.
9 *
10 * This file is distributed in the hope that it will be useful, but
11 * WITHOUT ANY WARRANTY; without even the implied warranty of
12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 * General Public License for more details.
14 *
15 * You should have received a copy of the GNU General Public License
16 * along with this file; if not, write to the Free Software
17 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
18 * 02110-1301, USA.
19 *
20 */
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21/** @file lib/arcfour.c
22 * @brief Arcfour (RC4-compatible) stream cipher implementation
23 *
24 * Code from Libgcrypt adapted for gnulib by Simon Josefsson.
25 *
fcdff139 26 * For a description of the algorithm, see:
132a5a4a 27 *
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28 * Bruce Schneier: Applied Cryptography. John Wiley & Sons, 1996.
29 * ISBN 0-471-11709-9. Pages 397 ff.
30 */
31
32#include "arcfour.h"
33
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34/** @brief Encrypt using Arcfour stream cipher
35 * @param context Context structure
36 * @param inbuf Input buffer
37 * @param outbuf Output buffer
38 * @param length Number of bytes in @p inbuf
39 *
40 * Copies from @p inbuf to @p outbuf, encrypting (or decrypting) using
41 * the stream controlled by @p context.
42 */
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43void
44arcfour_stream (arcfour_context * context, const char *inbuf, char *outbuf,
45 size_t length)
46{
47 uint8_t i = context->idx_i;
48 uint8_t j = context->idx_j;
49 char *sbox = context->sbox;
50
51 for (; length > 0; length--)
52 {
53 char t;
54
55 i++;
56 j += sbox[i];
57 t = sbox[i];
58 sbox[i] = sbox[j];
59 sbox[j] = t;
60 *outbuf++ = (*inbuf++
61 ^ sbox[(0U + sbox[i] + sbox[j]) % ARCFOUR_SBOX_SIZE]);
62 }
63
64 context->idx_i = i;
65 context->idx_j = j;
66}
67
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68/** @brief Initialize an @ref arcfour_context
69 * @param context Context structure
70 * @param key Key data
71 * @param keylen Length of key
72 *
73 * Initializes @p context using @p key.
74 */
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75void
76arcfour_setkey (arcfour_context * context, const char *key, size_t keylen)
77{
78 size_t i, j, k;
79 char *sbox = context->sbox;
80
81 context->idx_i = context->idx_j = 0;
82 for (i = 0; i < ARCFOUR_SBOX_SIZE; i++)
83 sbox[i] = i;
84 for (i = j = k = 0; i < ARCFOUR_SBOX_SIZE; i++)
85 {
86 char t;
87 j = (j + sbox[i] + key[k]) % ARCFOUR_SBOX_SIZE;
88 t = sbox[i];
89 sbox[i] = sbox[j];
90 sbox[j] = t;
91 if (++k == keylen)
92 k = 0;
93 }
94}