3 This file is part of the AVR-Crypto-Lib.
4 Copyright (C) 2008 Daniel Otte (daniel.otte@rub.de)
6 This program is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 This program is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
22 * email: daniel.otte@rub.de
24 * License: GPLv3 or later
25 * Description: Implementation of the ARCFOUR (RC4 compatible) stream cipher algorithm.
33 * length is length of key in bytes!
36 void arcfour_init(const void *key, uint16_t length_b, arcfour_ctx_t *ctx){
38 uint8_t length_B = length_b/8;
40 for(x=0; x<= 255; ++x)
43 for(x=0; x<= 255; ++x){
44 y += ctx->s[x] + ((uint8_t*)key)[x % length_B];
46 /* ctx->s[y] <--> ctx->s[x] */
48 ctx->s[y] = ctx->s[x];
54 uint8_t arcfour_gen(arcfour_ctx_t *ctx){
57 ctx->j += ctx->s[ctx->i];
58 /* ctx->s[i] <--> ctx->s[j] */
60 ctx->s[ctx->j] = ctx->s[ctx->i];
62 return ctx->s[(ctx->s[ctx->j] + ctx->s[ctx->i]) & 0xff];