/*! \brief Polled function that generates the last subkey of the Expanded Key
* needed during decryption.
*
* \note This code is blocking and will dead lock if no interrupt flags are set.
*
* \param key Pointer to AES key.
* \param last_sub_key Pointer to where the last subkey of the Expanded Key
* shall be stored.
*
* \retval true If generating the last subkey was successful.
* \retval false If generating the last subkey was not successful.
*/
bool AES_lastsubkey_generate(uint8_t * key, uint8_t * last_sub_key)
{
bool keygen_ok;
AES_software_reset();
/* Load key into AES key memory. */
uint8_t * temp_key = key;
for(uint8_t i = 0; i < AES_BLOCK_LENGTH; i++){
AES.KEY = *(temp_key++);
}
/* Load dummy data into AES state memory. */
for(uint8_t i = 0; i < AES_BLOCK_LENGTH; i++){
AES.STATE = 0x00;
}
/* Set AES in encryption mode and start AES. */
AES.CTRL = (AES.CTRL & (~AES_DECRYPT_bm)) | AES_START_bm;
do{
/* Wait until AES is finished or an error occurs. */
}while((AES.STATUS & (AES_SRIF_bm|AES_ERROR_bm) ) == 0);
/* If not error. */
if((AES.STATUS & AES_ERROR_bm) == 0){
/* Store the last subkey. */
uint8_t * temp_last_sub_key = last_sub_key;
for(uint8_t i = 0; i < AES_BLOCK_LENGTH; i++){
*(temp_last_sub_key++) = AES.KEY;
}
AES.STATUS = AES_SRIF_bm;
keygen_ok = true;
}else{
AES.STATUS = AES_ERROR_bm;
keygen_ok = false;
}
return keygen_ok;
}
int main( void )
{
/* Assume that everything is ok*/
success = true;
/* Before using the AES it is recommended to do an AES software reset to put
* the module in known state, in case other parts of your code has accessed
* the AES module. */
AES_software_reset();
/* Generate last subkey. */
AES_lastsubkey_generate(key, lastsubkey);
/* Do AES Cipher Block Chaining encryption and decryption on three blocks. */
success = AES_CBC_encrypt(); /* MODIFY THE FUNCTION CALL */
success = AES_CBC_decrypt(); /* MODIFY THE FUNCTION CALL */
/* Check if decrypted answer is equal to plaintext. */
for(uint8_t i = 0; i < BLOCK_LENGTH * BLOCK_COUNT ; i++ ){
if (data_block[i] != block_ans[i]){
success = false;
}
}
if(success){
while(true){
/* If the example ends up here every thing is ok. */
nop();
}
}else{
while(true){
/* If the example ends up here something is wrong. */
nop();
}
}
}