aes_driver.c

ATMEL XMEGA crypto program-task4.

}



/*! \brief  Polled function that does an AES decryption on one 128-bit data block.
 *
 *  \note This code is blocking and will dead lock if no interrupt flags are set.
 *
 *  \param  ciphertext  Pointer to the ciphertext that shall be decrypted
 *  \param  plaintext   Pointer to where in memory the plaintext (answer) shall be stored.
 *  \param  key         Pointer to the DES key
 *
 *  \retval true   If the AES decryption was successful.
 *  \retval false  If the AES decryption was not successful.
 */
bool AES_decrypt(uint8_t * ciphertext, uint8_t * plaintext,
                 uint8_t * key)
{
  	bool decrypt_ok;

	/* 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 data into AES state memory. */
	uint8_t * temp_ciphertext = ciphertext;
	for(uint8_t i = 0; i < AES_BLOCK_LENGTH; i++){
		AES.STATE =  *(temp_ciphertext++);
	}

	/* Set AES in decryption mode and start the AES.*/
	AES.CTRL |= (AES_START_bm | AES_DECRYPT_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 result. */
		uint8_t * temp_plaintext = plaintext;
		for(uint8_t i = 0; i < AES_BLOCK_LENGTH; i++){
			*(temp_plaintext++) = AES.STATE;
		}
		decrypt_ok = true;
	}else{
		decrypt_ok = false;

	}
	return decrypt_ok;
}




/*! \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;
}



/*! \brief  Polled function that does AES CBC encryption on a given number of
 *           128-bit data block.
 *
 *  \note This code is blocking and will dead lock if no interrupt flags are set.
 *
 *  \param  plaintext    Pointer to the plaintext that shall be encrypted.
 *  \param  ciphertext   Pointer to where in memory the ciphertext (answer) shall be stored.
 *  \param  key          Pointer to the key.
 *  \param  init	        Pointer to the initialization vector used in the CBC.
 *  \param  block_count  The number of blocks to encrypt.
 *
 *	\retval true:	The AES CBC encryption was successful.
 *  \retval false:  The AES CBC encryption was not successful.
 */
bool AES_CBC_encrypt(uint8_t * plaintext, uint8_t * ciphertext,
                     uint8_t * key, uint8_t * init, uint16_t block_count)
{
  	bool CBC_ok = true;

  	/* The first encryption uses the initialization vector. */
	uint8_t * temp_init = init;
	for(uint8_t i = 0; i < AES_BLOCK_LENGTH; i++){
		AES.STATE =  *(temp_init++);
	}

	/* Set AES in encryption mode and enables the XOR feature and the AUTO start
	 * mode. */
	AES.CTRL = (AES.CTRL & (~AES_DECRYPT_bm))| AES_XOR_bm |AES_AUTO_bm;

	/* Temporary values used to reduce memory access. */
	uint8_t * temp_plaintext = plaintext;
	uint8_t * temp_ciphertext = ciphertext;

	for(uint8_t blocks_left = block_count; blocks_left > 0; blocks_left--){

		/* 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 plaintext into AES state memory. Auto starts. */
		for(uint8_t i = 0; i < AES_BLOCK_LENGTH; i++){
			AES.STATE =  *(temp_plaintext++);
		}


		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 result. */
			uint8_t * temp = temp_ciphertext;
			for(uint8_t i = 0; i < AES_BLOCK_LENGTH; i++){
				*(temp++) = AES.STATE;
			}
			temp_ciphertext = temp;
		}else{
			CBC_ok = false;
		}
	}

	/* Turn off auto mode and xor feature. */
	AES.CTRL = (AES.CTRL & ~( AES_XOR_bm |AES_AUTO_bm));

	return CBC_ok;
}



/*! \brief  Polled function that does AES CBC decryption on a given number of
 *           128-bit data block.
 *
 *  \note This code is blocking and will dead lock if no interrupt flags are set.
 *
 *  \param  ciphertext   Pointer to the ciphertext that shall be decrypted.
 *  \param  plaintext    Pointer to where the plaintext (answer) shall be stored.
 *  \param  key          Pointer to the last subkey of the Expanded Key.
 *  \param  init	        Pointer to the initialization vector used in the CBC.
 *  \param  block_count  The number of blocks to decrypt.
 *
 *  \retval true   If the AES CBC decryption was successful.
 *  \retval false  If the AES CBC decryption was not successful.
 */
bool AES_CBC_decrypt(uint8_t * ciphertext, uint8_t * plaintext,
                     uint8_t * key, uint8_t * init, uint16_t block_count)
{
	bool CBC_ok = true;

	/* Temporary values used to reduce memory access. */
  	uint8_t * temp_plaintext = plaintext;
	uint8_t * temp_ciphertext = ciphertext;

	for(uint8_t blocks_left = block_count; blocks_left > 0; blocks_left--){

	  	/* 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 ciphertext into AES state memory. */
		uint8_t * temp = temp_ciphertext;
		for(uint8_t i = 0; i < AES_BLOCK_LENGTH; i++){
			AES.STATE =  *(temp++);
		}

		temp_ciphertext = temp;

		/* Set AES in decryption mode and enable xor feature and start the AES. */
		AES.CTRL |= (AES_DECRYPT_bm | AES_XOR_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){

			/* The first block is xored with the initialization vector. */
			if(blocks_left == block_count){
				/* Load into AES state memory. */
				uint8_t * temp_init = init;
				for(uint8_t i = 0; i < AES_BLOCK_LENGTH; i++){
					AES.STATE =  *(temp_init++);
				}
			}
			/* The other blocks is xored with the previous ciphertext block. */
			else{
				/* Load into AES state memory. */
			  	uint8_t * last_ciphertext = temp_ciphertext - (AES_BLOCK_LENGTH*2);
				for(uint8_t i = 0; i < AES_BLOCK_LENGTH; i++){
					AES.STATE =  *(last_ciphertext++);
				}
			}

			/* Disable XOR feature before next round. */
			AES.CTRL = AES.CTRL & (~AES_XOR_bm);

			/* Store the result. */
			uint8_t * temp = temp_plaintext;
			for(uint8_t i = 0; i < AES_BLOCK_LENGTH; i++){
				*(temp++) = AES.STATE;
			}
			temp_plaintext = temp;
		}else{
			CBC_ok = false;
		}

	}
	return CBC_ok;
}



/*! \brief  Function that sets AES interrupt level
 *
 *  \param  int_lvl  The AES interrupt level
 */
void AES_interruptlevel_set(AES_INTLVL_t int_lvl)
{
	AES.INTCTRL = int_lvl;
}




/*! \brief  Polled function that does an AES encryption on one 128-bit data block.
 *
 *  Function equal to the AES_encrypt function but the key is not loaded
 *  into the key memory. The function require that the key already is in the
 *  key memory. Used when encryption and decryption with the same key is
 *  done every other time.
 *
 *  \note This code is blocking and will dead lock if no interrupt flags are set.
 *
 *  \param  plaintext  Pointer to the plaintext that shall be encrypted
 *  \param  ciphertext Pointer to where in memory the ciphertext (answer) shall be stored.
 *
 *  \retval true   If the AES encryption was successful.
 *  \retval false  If the AES encryption was not successful.
 */
bool AES_encrypt_backtoback(uint8_t * plaintext, uint8_t * ciphertext)
{
  	bool encrypt_ok;

	/* Load data into AES state memory. */
	uint8_t * temp_plaintext = plaintext;
	for(uint8_t i = 0; i < AES_BLOCK_LENGTH; i++){
		AES.STATE =  *(temp_plaintext++);
	}

	/* 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 result. */
		uint8_t * temp_ciphertext = ciphertext;
		for(uint8_t i = 0; i < AES_BLOCK_LENGTH; i++){
			*(temp_ciphertext++) = AES.STATE;
		}
		encrypt_ok = true;
	}else{
		encrypt_ok = false;

	}
	return encrypt_ok;
}



/*! \brief  Polled function that does an AES decryption on one 128-bit data block.
 *
 *  Function equal to the AES_decrypt function but the key is not loaded
 *  into the key memory. The function require that the key already is in the
 *  key memory. Used when encryption and decryption with the same key is
 *  done every other time.
 *
 *  \note This code is blocking and will dead lock if no interrupt flags are set.
 *
 *  \param  ciphertext  Pointer to the ciphertext that shall be decrypted
 *  \param  plaintext   Pointer to where in memory the plaintext (answer) shall be stored.
 *
 *  \retval true   If the AES decryption was successful.
 *  \retval false  If the AES decryption was not successful.
 */
bool AES_decrypt_backtoback(uint8_t * ciphertext, uint8_t * plaintext)
{
  	bool decrypt_ok;

	/* Load data into AES state memory. */
	uint8_t * temp_ciphertext = ciphertext;
	for(uint8_t i = 0; i < AES_BLOCK_LENGTH; i++){
		AES.STATE =  *(temp_ciphertext++);
	}

	/* Set AES in decryption mode and start the AES.*/
	AES.CTRL |= (AES_START_bm | AES_DECRYPT_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 result. */
		uint8_t * temp_plaintext = plaintext;
		for(uint8_t i = 0; i < AES_BLOCK_LENGTH; i++){
			*(temp_plaintext++) = AES.STATE;
		}
		decrypt_ok = true;
	}else{
		decrypt_ok = false;

	}
	return decrypt_ok;
}