I know the AES is a symmetric encryption algotithm.
so the key of encrypt and decrypt is same.
Why gennerate the lastsubkey for decrypt?
#include "avr_compiler.h"
#include "AES_driver.h"
#define BLOCK_LENGTH 16
#define BLOCK_COUNT 3
/* Global Plaintext variable containing one block. */
uint8_t data[BLOCK_LENGTH] = {0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08,
0x09, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16};
/* Variable used to store the result from a single AES encryption/decryption .*/
uint8_t single_ans[BLOCK_LENGTH];
/* Key used when AES encryption is done operations. */
uint8_t key[BLOCK_LENGTH] = {0x94, 0x74, 0xB8, 0xE8, 0xC7, 0x3B, 0xCA, 0x7D,
0x28, 0x34, 0x76, 0xAB, 0x38, 0xCF, 0x37, 0xC2};
/* Key used when the AES shall decrypt. This key is a modified version of the key. */
uint8_t lastsubkey[BLOCK_LENGTH];
/* Initialisation vector used during Cipher Block Chaining. */
uint8_t init[BLOCK_LENGTH] = {0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77, 0x88,
0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77, 0x88};
/* Plain text used during Cipher Block Chaining(contains 3 blocks). */
uint8_t data_block[BLOCK_LENGTH * BLOCK_COUNT] =
{0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08,
0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F, 0x00,
0xAB, 0xBA, 0x00, 0x00, 0xDE, 0xAD, 0x00, 0x00,
0xAB, 0xBA, 0x00, 0x00, 0xDE, 0xAD, 0x00, 0x00,
0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08,
0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F, 0x00};
/* Variable used to store ciphertext from Cipher Block Chaining. */
uint8_t cipher_block_ans[BLOCK_LENGTH * BLOCK_COUNT];
/* Variable used to store decrypted plaintext from Cipher Block Chaining. */
uint8_t block_ans[BLOCK_LENGTH * BLOCK_COUNT];
/* Variable used to check if decrypted answer is equal original data. */
bool success;
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. */
0AES_lastsubkey_generate(key, lastsubkey);
/* Do AES encryption and decryption of a single block. */
success = AES_encrypt(data, single_ans, key);
success = AES_decrypt(single_ans, single_ans, lastsubkey);
/* Check if decrypted answer is equal to plaintext. */
for(uint8_t i = 0; i < BLOCK_LENGTH ; i++ ){
if (data[i] != single_ans[i]){
success = false;
}
}
/* Do AES Cipher Block Chaining encryption and decryption on three blocks. */
success = AES_CBC_encrypt(data_block, cipher_block_ans, key, init,
BLOCK_COUNT);
success = AES_CBC_decrypt(cipher_block_ans, block_ans, lastsubkey,
init, BLOCK_COUNT);
/* 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();
}
}
}