A5_1.c

   1 /* A5_1.c */
   2 /*
   3     This file is part of the Crypto-avr-lib/microcrypt-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  * Date:        24.06.2006
  23  * License: GPL
  24  * Description: Implementation of the A5/1 stream cipher algorithm, as used in GSM.
  25  * ! Warning, this is weak crypto !
  26  *
  27  */
  28
  29 #include <stdint.h>
  30 #include <string.h>
  31 #include "A5_1.h"
  32 #include <avr/pgmspace.h>
  33
  34 uint8_t a5_1_clock_core(a5_1_ctx_t *c, uint8_t clockoverride);
  35
  36
  37 /*
  38  * length is length of key in bytes!
  39  */
  40
  41 void a5_1_init(a5_1_ctx_t *c, void* key, uint8_t keylength_b, void* iv, uint8_t ivlength_b){
  42         uint8_t i,t;
  43         memset(c->r1, 0, 3);
  44         memset(c->r2, 0, 3);
  45         memset(c->r3, 0, 3);
  46         for(i=0; i<keylength_b; ++i){
  47                 t=((uint8_t*)key)[i/8];
  48                 t=1&(t>>i);
  49                 c->r1[0] ^= t;
  50                 c->r2[0] ^= t;
  51                 c->r3[0] ^= t;
  52                 a5_1_clock_core(c, 0x7);
  53         }
  54         for(i=0; i<ivlength_b; ++i){
  55                 t=((uint8_t*)iv)[i/8];
  56                 t=1&(t>>i);
  57                 c->r1[0] ^= t;
  58                 c->r2[0] ^= t;
  59                 c->r3[0] ^= t;
  60                 a5_1_clock_core(c, 0x7);
  61         }
  62         for(i=0; i<100; ++i)
  63                 a5_1_clock_core(c,0);
  64 }
  65
  66 static
  67 void shiftreg(uint8_t* d){
  68         uint8_t c, c2;
  69         c=d[0]>>7;
  70         d[0] <<= 1;
  71         c2=d[1]>>7;
  72         d[1] = (d[1]<<1) | c;
  73         d[2] = (d[2]<<1) | c2;
  74 }
  75
  76         uint8_t parity3_lut[] PROGMEM = {0, 1, 1, 0,
  77                                              1, 0, 0, 1};
  78         uint8_t clock_lut[] PROGMEM =  {0x7, 0x6, 0x5, 0x3,
  79                                             0x3, 0x5, 0x6, 0x7};
  80
  81 uint8_t a5_1_clock_core(a5_1_ctx_t *c, uint8_t clockoverride){
  82         uint8_t ret,clk,fb;
  83         ret = (0x04&c->r1[2]) | (0x20&c->r2[2]) | (0x40&c->r3[2]);
  84         ret = ret^(ret>>6);
  85         ret &= 0x7;
  86         ret = pgm_read_byte(parity3_lut+ret);
  87         clk = (0x08&c->r1[1]) | (0x10&c->r2[1]) | (0x20&c->r3[1]);
  88         clk >>= 3;
  89         clk = pgm_read_byte(clock_lut+clk);
  90         clk |= clockoverride;
  91
  92         if(clk&1){
  93                 fb = c->r1[2] ^ (1&((c->r1[1])>>5));
  94                 fb &= 0x7;
  95                 fb = pgm_read_byte(parity3_lut+fb);
  96                 shiftreg(c->r1);
  97                 c->r1[0] |= fb;
  98                 c->r1[2] &= 0x07;
  99         }
 100         clk>>=1;
 101         if(clk&1){
 102                 fb = c->r2[2]>>4 ;
 103                 fb &= 0x7;
 104                 fb = pgm_read_byte(parity3_lut+fb);
 105                 shiftreg(c->r2);
 106                 c->r2[0] |= fb;
 107                 c->r2[2] &= 0x3F;
 108
 109         }
 110         clk>>=1;
 111         if(clk&1){
 112                 fb = (c->r3[2]>>4) ^ (1&((c->r3[0])>>7));
 113                 fb &= 0x7;
 114                 fb = pgm_read_byte(parity3_lut+fb);
 115                 shiftreg(c->r3);
 116                 c->r3[0] |= fb;
 117                 c->r3[2] &= 0x7F;
 118         }
 119         return ret;
 120 }
 121
 122 uint8_t a5_1_clock(a5_1_ctx_t *c){
 123         return a5_1_clock_core(c, 0);
 124 }
 125
 126
 127 uint8_t a5_1_gen(a5_1_ctx_t *c){
 128         uint8_t ret=0;
 129         ret = a5_1_clock(c);
 130         ret <<= 1;
 131         ret = a5_1_clock(c);
 132         ret <<= 1;
 133         ret = a5_1_clock(c);
 134         ret <<= 1;
 135         ret = a5_1_clock(c);
 136         ret <<= 1;
 137         ret = a5_1_clock(c);
 138         ret <<= 1;
 139         ret = a5_1_clock(c);
 140         ret <<= 1;
 141         ret = a5_1_clock(c);
 142         ret <<= 1;
 143         ret = a5_1_clock(c);
 144         return ret;
 145 }
 146
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