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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 }