new AES in C, happy new year

[avr-crypto-lib.git] / aes_dec.c

diff --git a/aes_dec.c b/aes_dec.c
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+++ b/aes_dec.c
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+/* aes.c */
+/*
+    This file is part of the Crypto-avr-lib/microcrypt-lib.
+    Copyright (C) 2008  Daniel Otte (daniel.otte@rub.de)
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#include <stdint.h>
+#include <string.h>
+#include "gf256mul.h"
+#include "aes.h"
+#include "aes_invsbox.h"
+#include "aes_dec.h"
+#include <avr/pgmspace.h>
+
+void aes_invshiftrow(void* data, uint8_t shift){
+       uint8_t tmp[4];
+       tmp[0] = ((uint8_t*)data)[(4+0-shift)&3];
+       tmp[1] = ((uint8_t*)data)[(4+1-shift)&3];
+       tmp[2] = ((uint8_t*)data)[(4+2-shift)&3];
+       tmp[3] = ((uint8_t*)data)[(4+3-shift)&3];
+       memcpy(data, tmp, 4);
+}
+
+static
+void aes_dec_round(aes_cipher_state_t* state, const aes_roundkey_t* k){
+       uint8_t tmp[16];
+       uint8_t i;
+       /* keyAdd */
+       for(i=0; i<16; ++i){
+               tmp[i] = state->s[i] ^ k->ks[i];
+       }
+       /* mixColums */
+       for(i=0; i<4; ++i){
+               state->s[4*0+i] =
+                         gf256mul(0xe, tmp[4*0+i], 0x1b)
+                       ^ gf256mul(0xb, tmp[4*1+i], 0x1b)
+                       ^ gf256mul(0xd, tmp[4*2+i], 0x1b)
+                       ^ gf256mul(0x9, tmp[4*3+i], 0x1b);
+               state->s[4*1+i] =
+                         gf256mul(0x9, tmp[4*0+i], 0x1b)
+                       ^ gf256mul(0xe, tmp[4*1+i], 0x1b)
+                       ^ gf256mul(0xb, tmp[4*2+i], 0x1b)
+                       ^ gf256mul(0xd, tmp[4*3+i], 0x1b);
+               state->s[4*2+i] =
+                         gf256mul(0xd, tmp[4*0+i], 0x1b)
+                       ^ gf256mul(0x9, tmp[4*1+i], 0x1b)
+                       ^ gf256mul(0xe, tmp[4*2+i], 0x1b)
+                       ^ gf256mul(0xb, tmp[4*3+i], 0x1b);
+               state->s[4*3+i] =
+                         gf256mul(0xb, tmp[4*0+i], 0x1b)
+                       ^ gf256mul(0xd, tmp[4*1+i], 0x1b)
+                       ^ gf256mul(0x9, tmp[4*2+i], 0x1b)
+                       ^ gf256mul(0xe, tmp[4*3+i], 0x1b);
+       }       
+       /* shiftRows */
+       aes_invshiftrow(state->s+4, 1);
+       aes_invshiftrow(state->s+8, 2);
+       aes_invshiftrow(state->s+12, 3);                
+       /* subBytes */
+       for(i=0; i<16; ++i){
+               state->s[i] = pgm_read_byte(aes_invsbox+state->s[i]);
+       }
+}
+
+
+static
+void aes_dec_firstround(aes_cipher_state_t* state, const aes_roundkey_t* k){
+       uint8_t i;
+       /* keyAdd */
+       for(i=0; i<16; ++i){
+               state->s[i] ^= k->ks[i];
+       }
+       /* shiftRows */
+       aes_invshiftrow(state->s+4, 1);
+       aes_invshiftrow(state->s+8, 2);
+       aes_invshiftrow(state->s+12, 3);                
+       /* subBytes */
+       for(i=0; i<16; ++i){
+               state->s[i] = pgm_read_byte(aes_invsbox+state->s[i]);
+       }
+}
+
+void aes_decrypt_core(aes_cipher_state_t* state, const aes_genctx_t* ks, uint8_t rounds){
+       uint8_t i;
+       aes_dec_firstround(state, &(ks->key[i=rounds]));
+       for(;rounds>1;--rounds){
+               --i;
+               aes_dec_round(state, &(ks->key[i]));
+       }
+       for(i=0; i<16; ++i){
+               state->s[i] ^= ks->key[0].ks[i];
+       }
+}