aes/aes_dec.c

   1 /* aes.c */
   2 /*
   3     This file is part of the AVR-Crypto-Lib.
   4     Copyright (C) 2008, 2009  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 #include <stdint.h>
  21 #include <string.h>
  22 #include "gf256mul.h"
  23 #include "aes.h"
  24 #include "aes_invsbox.h"
  25 #include "aes_dec.h"
  26 #include <avr/pgmspace.h>
  27
  28 void aes_invshiftrow(void *data, uint8_t shift){
  29         uint8_t tmp[4];
  30         tmp[0] = ((uint8_t*)data)[(4+0-shift)&3];
  31         tmp[1] = ((uint8_t*)data)[(4+1-shift)&3];
  32         tmp[2] = ((uint8_t*)data)[(4+2-shift)&3];
  33         tmp[3] = ((uint8_t*)data)[(4+3-shift)&3];
  34         memcpy(data, tmp, 4);
  35 }
  36
  37 void aes_invshiftcol(void *data, uint8_t shift){
  38         uint8_t tmp[4];
  39         tmp[0] = ((uint8_t*)data)[ 0];
  40         tmp[1] = ((uint8_t*)data)[ 4];
  41         tmp[2] = ((uint8_t*)data)[ 8];
  42         tmp[3] = ((uint8_t*)data)[12];
  43         ((uint8_t*)data)[ 0] = tmp[(4-shift+0)&3];
  44         ((uint8_t*)data)[ 4] = tmp[(4-shift+1)&3];
  45         ((uint8_t*)data)[ 8] = tmp[(4-shift+2)&3];
  46         ((uint8_t*)data)[12] = tmp[(4-shift+3)&3];
  47 }
  48 static
  49 void aes_dec_round(aes_cipher_state_t *state, const aes_roundkey_t *k){
  50         uint8_t tmp[16];
  51         uint8_t i;
  52         uint8_t t,u,v,w;
  53         /* keyAdd */
  54         for(i=0; i<16; ++i){
  55                 tmp[i] = state->s[i] ^ k->ks[i];
  56         }
  57         /* mixColums */
  58         for(i=0; i<4; ++i){
  59                 t = tmp[4*i+3] ^ tmp[4*i+2];
  60                 u = tmp[4*i+1] ^ tmp[4*i+0];
  61                 v = t ^ u;
  62                 v = gf256mul(0x09, v, 0x1b);
  63                 w = v ^ gf256mul(0x04, tmp[4*i+2] ^ tmp[4*i+0], 0x1b);
  64                 v = v ^ gf256mul(0x04, tmp[4*i+3] ^ tmp[4*i+1], 0x1b);
  65                 state->s[4*i+3] = tmp[4*i+3] ^ v ^ gf256mul(0x02, tmp[4*i+0] ^ tmp[4*i+3], 0x1b);
  66                 state->s[4*i+2] = tmp[4*i+2] ^ w ^ gf256mul(0x02, t, 0x1b);
  67                 state->s[4*i+1] = tmp[4*i+1] ^ v ^ gf256mul(0x02, tmp[4*i+2] ^ tmp[4*i+1], 0x1b);
  68                 state->s[4*i+0] = tmp[4*i+0] ^ w ^ gf256mul(0x02, u, 0x1b);
  69
  70                 /*
  71                 state->s[4*i+0] =
  72                           gf256mul(0xe, tmp[4*i+0], 0x1b)
  73                         ^ gf256mul(0xb, tmp[4*i+1], 0x1b)
  74                         ^ gf256mul(0xd, tmp[4*i+2], 0x1b)
  75                         ^ gf256mul(0x9, tmp[4*i+3], 0x1b);
  76                 state->s[4*i+1] =
  77                           gf256mul(0x9, tmp[4*i+0], 0x1b)
  78                         ^ gf256mul(0xe, tmp[4*i+1], 0x1b)
  79                         ^ gf256mul(0xb, tmp[4*i+2], 0x1b)
  80                         ^ gf256mul(0xd, tmp[4*i+3], 0x1b);
  81                 state->s[4*i+2] =
  82                           gf256mul(0xd, tmp[4*i+0], 0x1b)
  83                         ^ gf256mul(0x9, tmp[4*i+1], 0x1b)
  84                         ^ gf256mul(0xe, tmp[4*i+2], 0x1b)
  85                         ^ gf256mul(0xb, tmp[4*i+3], 0x1b);
  86                 state->s[4*i+3] =
  87                           gf256mul(0xb, tmp[4*i+0], 0x1b)
  88                         ^ gf256mul(0xd, tmp[4*i+1], 0x1b)
  89                         ^ gf256mul(0x9, tmp[4*i+2], 0x1b)
  90                         ^ gf256mul(0xe, tmp[4*i+3], 0x1b);
  91                 */
  92         }
  93         /* shiftRows */
  94         aes_invshiftcol(state->s+1, 1);
  95         aes_invshiftcol(state->s+2, 2);
  96         aes_invshiftcol(state->s+3, 3);
  97         /* subBytes */
  98         for(i=0; i<16; ++i){
  99                 state->s[i] = pgm_read_byte(aes_invsbox+state->s[i]);
 100         }
 101 }
 102
 103
 104 static
 105 void aes_dec_firstround(aes_cipher_state_t *state, const aes_roundkey_t *k){
 106         uint8_t i;
 107         /* keyAdd */
 108         for(i=0; i<16; ++i){
 109                 state->s[i] ^= k->ks[i];
 110         }
 111         /* shiftRows */
 112         aes_invshiftcol(state->s+1, 1);
 113         aes_invshiftcol(state->s+2, 2);
 114         aes_invshiftcol(state->s+3, 3);
 115         /* subBytes */
 116         for(i=0; i<16; ++i){
 117                 state->s[i] = pgm_read_byte(aes_invsbox+state->s[i]);
 118         }
 119 }
 120
 121 void aes_decrypt_core(aes_cipher_state_t *state, const aes_genctx_t *ks, uint8_t rounds){
 122         uint8_t i;
 123         aes_dec_firstround(state, &(ks->key[i=rounds]));
 124         for(;rounds>1;--rounds){
 125                 --i;
 126                 aes_dec_round(state, &(ks->key[i]));
 127         }
 128         for(i=0; i<16; ++i){
 129                 state->s[i] ^= ks->key[0].ks[i];
 130         }
 131 }