1 /* arcfour.c --- The arcfour stream cipher
2 * Copyright (C) 2000, 2001, 2002, 2003, 2005, 2006 Free Software
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
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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.
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
21 /** @file lib/arcfour.c
22 * @brief Arcfour (RC4-compatible) stream cipher implementation
24 * Code from Libgcrypt adapted for gnulib by Simon Josefsson.
26 * For a description of the algorithm, see:
28 * Bruce Schneier: Applied Cryptography. John Wiley & Sons, 1996.
29 * ISBN 0-471-11709-9. Pages 397 ff.
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
40 * Copies from @p inbuf to @p outbuf, encrypting (or decrypting) using
41 * the stream controlled by @p context.
44 arcfour_stream (arcfour_context * context, const char *inbuf, char *outbuf,
47 uint8_t i = context->idx_i;
48 uint8_t j = context->idx_j;
49 char *sbox = context->sbox;
51 for (; length > 0; length--)
61 ^ sbox[(0U + sbox[i] + sbox[j]) % ARCFOUR_SBOX_SIZE]);
68 /** @brief Initialize an @ref arcfour_context
69 * @param context Context structure
71 * @param keylen Length of key
73 * Initializes @p context using @p key.
76 arcfour_setkey (arcfour_context * context, const char *key, size_t keylen)
79 char *sbox = context->sbox;
81 context->idx_i = context->idx_j = 0;
82 for (i = 0; i < ARCFOUR_SBOX_SIZE; i++)
84 for (i = j = k = 0; i < ARCFOUR_SBOX_SIZE; i++)
87 j = (j + sbox[i] + key[k]) % ARCFOUR_SBOX_SIZE;