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fcdff139 RK |
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 | */ | |
21 | ||
22 | /* Code from Libgcrypt adapted for gnulib by Simon Josefsson. */ | |
23 | ||
24 | /* | |
25 | * For a description of the algorithm, see: | |
26 | * Bruce Schneier: Applied Cryptography. John Wiley & Sons, 1996. | |
27 | * ISBN 0-471-11709-9. Pages 397 ff. | |
28 | */ | |
29 | ||
30 | #include "arcfour.h" | |
31 | ||
32 | void | |
33 | arcfour_stream (arcfour_context * context, const char *inbuf, char *outbuf, | |
34 | size_t length) | |
35 | { | |
36 | uint8_t i = context->idx_i; | |
37 | uint8_t j = context->idx_j; | |
38 | char *sbox = context->sbox; | |
39 | ||
40 | for (; length > 0; length--) | |
41 | { | |
42 | char t; | |
43 | ||
44 | i++; | |
45 | j += sbox[i]; | |
46 | t = sbox[i]; | |
47 | sbox[i] = sbox[j]; | |
48 | sbox[j] = t; | |
49 | *outbuf++ = (*inbuf++ | |
50 | ^ sbox[(0U + sbox[i] + sbox[j]) % ARCFOUR_SBOX_SIZE]); | |
51 | } | |
52 | ||
53 | context->idx_i = i; | |
54 | context->idx_j = j; | |
55 | } | |
56 | ||
57 | void | |
58 | arcfour_setkey (arcfour_context * context, const char *key, size_t keylen) | |
59 | { | |
60 | size_t i, j, k; | |
61 | char *sbox = context->sbox; | |
62 | ||
63 | context->idx_i = context->idx_j = 0; | |
64 | for (i = 0; i < ARCFOUR_SBOX_SIZE; i++) | |
65 | sbox[i] = i; | |
66 | for (i = j = k = 0; i < ARCFOUR_SBOX_SIZE; i++) | |
67 | { | |
68 | char t; | |
69 | j = (j + sbox[i] + key[k]) % ARCFOUR_SBOX_SIZE; | |
70 | t = sbox[i]; | |
71 | sbox[i] = sbox[j]; | |
72 | sbox[j] = t; | |
73 | if (++k == keylen) | |
74 | k = 0; | |
75 | } | |
76 | } |