Velciu Veronica-Mihaela - AAC

Nowadays, security becomes a great concern, as the devices start to process more and more sensitive data, leading to an increased number of attacks. The nodes in an wireless sensors network usually collect environment-related information and then send the data to a gateway, in order to be processed. There might be cases when the collected information leaks sensitive user data, so encrypting the communication would be a good practice is this cases. This project proposes and implements a method of securing the radio communication using symmetric cryptography on Sparrow v4 nodes.

The security module (AES) is characterized by:

• Hardware accelerated encryption and decryption;
• Compatible with AES-128 standard (128 bit key and data block size);
• ECB (encryption/decryption) mode and CBC (encryption) mode support;
• Stand-alone operation, independent of other blocks;
• Uses 16MHz crystal clock of the transceiver;

Controlling the security block is possible over 5 Registers within AVR I/O space:

• AES_STATUS - AES status register
• AES_CTRL - AES control register
• AES_KEY - Access to 16 Byte key buffer
• AES_STATE - Access to 16 Byte data buffer

The use of the security module requires a configuration of the security engine before starting a security operation. The following steps are required:

1. Key Setup - Write encryption or decryption key to KEY buffer (16 consecutive byte writes to AES_KEY)
2. AES configuration:
   • Select AES mode: ECB or CBC
   • Select encryption or decryption
   • Enable the AES Encryption Ready Interrupt AES_READY, if needed
3. Write Data - Write plain text or cipher text to DATA buffer (16 consecutive byte writes to AES_STATE)
4. Start operation - Start AES operation
5. Wait until AES encryption/decryption is finished: AES_READY IRQ or polling AES_DONE bit (register AES_STATUS)
6. Read Data - Read cipher text or plain text from DATA buffer (16 consecutive byte reads from AES_STATE)

In order to make use of the Security module presented in the previous section, I implemented a driver exposed as an Arduino library named AES. The library has the following interface:

void encryptECB(uint8_t *key, uint8_t *plaintext, uint8_t len, uint8_t *ciphertext);
void decryptECB(uint8_t *key, uint8_t *ciphertext, uint8_t len, uint8_t *plaintext);
void encryptCBC(uint8_t *key, uint8_t *iv, uint8_t *plaintext, uint8_t len, uint8_t *ciphertext);