151 lines
3.3 KiB
C
151 lines
3.3 KiB
C
/* A5_1.c */
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/*
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This file is part of the AVR-Crypto-Lib.
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Copyright (C) 2008 Daniel Otte (daniel.otte@rub.de)
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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: A5_1.c
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* Author: Daniel Otte
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* email: daniel.otte@rub.de
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* Date: 2006-06-24
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* License: GPLv3 or later
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* Description: Implementation of the A5/1 stream cipher algorithm, as used in GSM.
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* ! Warning, this is weak crypto !
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*
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*/
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#include <stdint.h>
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#include <string.h>
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#include "A5_1.h"
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#include <avr/pgmspace.h>
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uint8_t a5_1_clock_core(a5_1_ctx_t *c, uint8_t clockoverride);
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/*
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* length is length of key in bits!
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*/
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void a5_1_init(a5_1_ctx_t *c, void *key, uint8_t keylength_b, void *iv, uint8_t ivlength_b){
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uint8_t i,t;
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memset(c->r1, 0, 3);
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memset(c->r2, 0, 3);
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memset(c->r3, 0, 3);
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for(i=0; i<keylength_b; ++i){
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t=((uint8_t*)key)[i/8];
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t=1&(t>>i);
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c->r1[0] ^= t;
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c->r2[0] ^= t;
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c->r3[0] ^= t;
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a5_1_clock_core(c, 0x7);
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}
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for(i=0; i<ivlength_b; ++i){
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t=((uint8_t*)iv)[i/8];
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t=1&(t>>i);
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c->r1[0] ^= t;
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c->r2[0] ^= t;
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c->r3[0] ^= t;
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a5_1_clock_core(c, 0x7);
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}
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for(i=0; i<100; ++i)
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a5_1_clock_core(c,0);
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}
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static
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void shiftreg(uint8_t *d){
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uint8_t c, c2;
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c=d[0]>>7;
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d[0] <<= 1;
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c2=d[1]>>7;
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d[1] = (d[1]<<1) | c;
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d[2] = (d[2]<<1) | c2;
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}
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const uint8_t parity3_lut[] PROGMEM = {0, 1, 1, 0,
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1, 0, 0, 1};
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const uint8_t clock_lut[] PROGMEM = {0x7, 0x6, 0x5, 0x3,
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0x3, 0x5, 0x6, 0x7};
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uint8_t a5_1_clock_core(a5_1_ctx_t *c, uint8_t clockoverride){
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uint8_t ret,clk,fb;
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ret = (0x04&c->r1[2]) | (0x20&c->r2[2]) | (0x40&c->r3[2]);
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ret = ret^(ret>>6);
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ret &= 0x7;
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ret = pgm_read_byte(parity3_lut+ret);
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clk = (0x08&c->r1[1]) | (0x10&c->r2[1]) | (0x20&c->r3[1]);
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clk >>= 3;
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clk = pgm_read_byte(clock_lut+clk);
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clk |= clockoverride;
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if(clk&1){
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fb = c->r1[2] ^ (1&((c->r1[1])>>5));
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fb &= 0x7;
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fb = pgm_read_byte(parity3_lut+fb);
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shiftreg(c->r1);
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c->r1[0] |= fb;
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c->r1[2] &= 0x07;
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}
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clk>>=1;
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if(clk&1){
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fb = c->r2[2]>>4 ;
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fb &= 0x7;
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fb = pgm_read_byte(parity3_lut+fb);
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shiftreg(c->r2);
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c->r2[0] |= fb;
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c->r2[2] &= 0x3F;
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}
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clk>>=1;
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if(clk&1){
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fb = (c->r3[2]>>4) ^ (1&((c->r3[0])>>7));
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fb &= 0x7;
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fb = pgm_read_byte(parity3_lut+fb);
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shiftreg(c->r3);
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c->r3[0] |= fb;
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c->r3[2] &= 0x7F;
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}
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return ret;
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}
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uint8_t a5_1_clock(a5_1_ctx_t *c){
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return a5_1_clock_core(c, 0);
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}
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uint8_t a5_1_gen(a5_1_ctx_t *c){
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uint8_t ret=0;
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ret = a5_1_clock(c);
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ret <<= 1;
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ret = a5_1_clock(c);
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ret <<= 1;
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ret = a5_1_clock(c);
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ret <<= 1;
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ret = a5_1_clock(c);
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ret <<= 1;
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ret = a5_1_clock(c);
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ret <<= 1;
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ret = a5_1_clock(c);
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ret <<= 1;
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ret = a5_1_clock(c);
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ret <<= 1;
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ret = a5_1_clock(c);
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return ret;
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}
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