a51/A5_1.c

   1 /* A5_1.c */
   2 /*
   3     This file is part of the AVR-Crypto-Lib.
   4     Copyright (C) 2008  Daniel Otte (daniel.otte@rub.de)
   5
   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.
  10
  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.
  15
  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/>.
  18 */
  19 /*
  20  * File:        A5_1.c
  21  * Author:      Daniel Otte
  22  * email:       daniel.otte@rub.de
  23  * Date:        2006-06-24
  24  * License:     GPLv3 or later
  25  * Description: Implementation of the A5/1 stream cipher algorithm, as used in GSM.
  26  * ! Warning, this is weak crypto !
  27  *
  28  */
  29
  30 #include <stdint.h>
  31 #include <string.h>
  32 #include "A5_1.h"
  33 #include <avr/pgmspace.h>
  34
  35 uint8_t a5_1_clock_core(a5_1_ctx_t *c, uint8_t clockoverride);
  36
  37
  38 /*
  39  * length is length of key in bits!
  40  */
  41
  42 void a5_1_init(a5_1_ctx_t *c, void *key, uint8_t keylength_b, void *iv, uint8_t ivlength_b){
  43         uint8_t i,t;
  44         memset(c->r1, 0, 3);
  45         memset(c->r2, 0, 3);
  46         memset(c->r3, 0, 3);
  47         for(i=0; i<keylength_b; ++i){
  48                 t=((uint8_t*)key)[i/8];
  49                 t=1&(t>>i);
  50                 c->r1[0] ^= t;
  51                 c->r2[0] ^= t;
  52                 c->r3[0] ^= t;
  53                 a5_1_clock_core(c, 0x7);
  54         }
  55         for(i=0; i<ivlength_b; ++i){
  56                 t=((uint8_t*)iv)[i/8];
  57                 t=1&(t>>i);
  58                 c->r1[0] ^= t;
  59                 c->r2[0] ^= t;
  60                 c->r3[0] ^= t;
  61                 a5_1_clock_core(c, 0x7);
  62         }
  63         for(i=0; i<100; ++i)
  64                 a5_1_clock_core(c,0);
  65 }
  66
  67 static
  68 void shiftreg(uint8_t *d){
  69         uint8_t c, c2;
  70         c=d[0]>>7;
  71         d[0] <<= 1;
  72         c2=d[1]>>7;
  73         d[1] = (d[1]<<1) | c;
  74         d[2] = (d[2]<<1) | c2;
  75 }
  76
  77 const uint8_t parity3_lut[] PROGMEM = {0, 1, 1, 0,
  78                                              1, 0, 0, 1};
  79 const uint8_t clock_lut[] PROGMEM =  {0x7, 0x6, 0x5, 0x3,
  80                                             0x3, 0x5, 0x6, 0x7};
  81
  82 uint8_t a5_1_clock_core(a5_1_ctx_t *c, uint8_t clockoverride){
  83         uint8_t ret,clk,fb;
  84         ret = (0x04&c->r1[2]) | (0x20&c->r2[2]) | (0x40&c->r3[2]);
  85         ret = ret^(ret>>6);
  86         ret &= 0x7;
  87         ret = pgm_read_byte(parity3_lut+ret);
  88         clk = (0x08&c->r1[1]) | (0x10&c->r2[1]) | (0x20&c->r3[1]);
  89         clk >>= 3;
  90         clk = pgm_read_byte(clock_lut+clk);
  91         clk |= clockoverride;
  92
  93         if(clk&1){
  94                 fb = c->r1[2] ^ (1&((c->r1[1])>>5));
  95                 fb &= 0x7;
  96                 fb = pgm_read_byte(parity3_lut+fb);
  97                 shiftreg(c->r1);
  98                 c->r1[0] |= fb;
  99                 c->r1[2] &= 0x07;
 100         }
 101         clk>>=1;
 102         if(clk&1){
 103                 fb = c->r2[2]>>4 ;
 104                 fb &= 0x7;
 105                 fb = pgm_read_byte(parity3_lut+fb);
 106                 shiftreg(c->r2);
 107                 c->r2[0] |= fb;
 108                 c->r2[2] &= 0x3F;
 109
 110         }
 111         clk>>=1;
 112         if(clk&1){
 113                 fb = (c->r3[2]>>4) ^ (1&((c->r3[0])>>7));
 114                 fb &= 0x7;
 115                 fb = pgm_read_byte(parity3_lut+fb);
 116                 shiftreg(c->r3);
 117                 c->r3[0] |= fb;
 118                 c->r3[2] &= 0x7F;
 119         }
 120         return ret;
 121 }
 122
 123 uint8_t a5_1_clock(a5_1_ctx_t *c){
 124         return a5_1_clock_core(c, 0);
 125 }
 126
 127
 128 uint8_t a5_1_gen(a5_1_ctx_t *c){
 129         uint8_t ret=0;
 130         ret = a5_1_clock(c);
 131         ret <<= 1;
 132         ret = a5_1_clock(c);
 133         ret <<= 1;
 134         ret = a5_1_clock(c);
 135         ret <<= 1;
 136         ret = a5_1_clock(c);
 137         ret <<= 1;
 138         ret = a5_1_clock(c);
 139         ret <<= 1;
 140         ret = a5_1_clock(c);
 141         ret <<= 1;
 142         ret = a5_1_clock(c);
 143         ret <<= 1;
 144         ret = a5_1_clock(c);
 145         return ret;
 146 }
 147
 148
 149
 150