75 lines
1.9 KiB
C
75 lines
1.9 KiB
C
/* arcfour.c */
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/*
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This file is part of the AVR-Crypto-Lib.
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Copyright (C) 2006-2015 Daniel Otte (bg@nerilex.org)
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This program is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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/*
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* File: arcfour.c
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* Author: Daniel Otte
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* email: bg@nerilex.org
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* Date: 2006-06-07
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* License: GPLv3 or later
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* Description: Implementation of the ARCFOUR (RC4 compatible) stream cipher algorithm.
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*
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*/
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#include <stdint.h>
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#include "arcfour.h"
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/*
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* length is length of key in bytes!
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*/
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void arcfour_init(const void *key, uint16_t length_b, arcfour_ctx_t *ctx)
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{
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uint8_t t;
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const uint8_t length_B = length_b / 8;
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uint8_t nidx = length_B;
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uint8_t x = 0, y = 0;
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const uint8_t *kptr = (const uint8_t*) key;
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do {
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ctx->s[x] = x;
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} while ((uint8_t) ++x);
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do {
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y += ctx->s[x] + *kptr++;
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if (!--nidx) {
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kptr = (const uint8_t*) key;
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nidx = length_B;
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}
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y &= 0xff;
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/* ctx->s[y] <--> ctx->s[x] */
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t = ctx->s[y];
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ctx->s[y] = ctx->s[x];
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ctx->s[x] = t;
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} while ((uint8_t) ++x);
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ctx->i = ctx->j = 0;
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}
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uint8_t arcfour_gen(arcfour_ctx_t *ctx)
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{
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uint8_t t;
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ctx->i++;
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ctx->j += ctx->s[ctx->i];
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/* ctx->s[i] <--> ctx->s[j] */
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t = ctx->s[ctx->j];
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ctx->s[ctx->j] = ctx->s[ctx->i];
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ctx->s[ctx->i] = t;
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return ctx->s[(ctx->s[ctx->j] + ctx->s[ctx->i]) & 0xff];
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}
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