Quick Start Guide for AES - Basic

The supported board list:

• SAM L21 Xplained Pro
• SAM L22 Xplained Pro

This example demonstrates how to use the AES driver to perform:

• ECB encryption and decryption

Upon startup, the program uses the USART driver to display application output message from which ECB encryption/decryption modes can be tested.

Quick Start

Prerequisites

There are no prerequisites for this use case.

Code

Add to the main application source file, outside of any functions:

#define AES_EXAMPLE_REFBUF_SIZE 4

/* @{ */
uint32_t ref_plain_text[AES_EXAMPLE_REFBUF_SIZE] = {
    0xe2bec16b,
    0x969f402e,
    0x117e3de9,
    0x2a179373
};

uint32_t ref_cipher_text_ecb[AES_EXAMPLE_REFBUF_SIZE] = {
    0xb47bd73a,
    0x60367a0d,
    0xf3ca9ea8,
    0x97ef6624
};

const uint32_t key128[4] = {
    0x16157e2b,
    0xa6d2ae28,
    0x8815f7ab,
    0x3c4fcf09
};
/* @} */

Add to the main application source file, outside of any functions:

/* Output data array */
static uint32_t output_data[AES_EXAMPLE_REFBUF_SIZE];

/* State indicate */
volatile bool state = false;
/* AES configuration */
struct aes_config g_aes_cfg;
/* AES instance*/
struct aes_module aes_instance;
struct usart_module usart_instance;

Copy-paste the following setup code to your user application:

static void configure_usart(void)
{

    struct usart_config config_usart;
    usart_get_config_defaults(&config_usart);
    config_usart.baudrate    = 38400;
    config_usart.mux_setting = EDBG_CDC_SERCOM_MUX_SETTING;
    config_usart.pinmux_pad0 = EDBG_CDC_SERCOM_PINMUX_PAD0;
    config_usart.pinmux_pad1 = EDBG_CDC_SERCOM_PINMUX_PAD1;
    config_usart.pinmux_pad2 = EDBG_CDC_SERCOM_PINMUX_PAD2;
    config_usart.pinmux_pad3 = EDBG_CDC_SERCOM_PINMUX_PAD3;
    stdio_serial_init(&usart_instance, EDBG_CDC_MODULE, &config_usart);
    usart_enable(&usart_instance);
}

static void ecb_mode_test(void)
{
    printf("\r\n-----------------------------------\r\n");
    printf("- 128bit cryptographic key\r\n");
    printf("- ECB cipher mode\r\n");
    printf("- Auto start mode\r\n");
    printf("- 4 32bit words\r\n");
    printf("-----------------------------------\r\n");


    state = false;

    /* Configure the AES. */
    g_aes_cfg.encrypt_mode = AES_ENCRYPTION;
    g_aes_cfg.key_size = AES_KEY_SIZE_128;
    g_aes_cfg.start_mode = AES_AUTO_START;
    g_aes_cfg.opmode = AES_ECB_MODE;
    g_aes_cfg.cfb_size = AES_CFB_SIZE_128;
    g_aes_cfg.lod = false;
    aes_set_config(&aes_instance,AES, &g_aes_cfg);

    /* Set the cryptographic key. */
    aes_write_key(&aes_instance, key128);

    /* The initialization vector is not used by the ECB cipher mode. */

    aes_set_new_message(&aes_instance);
    /* Write the data to be ciphered to the input data registers. */
    aes_write_input_data(&aes_instance, ref_plain_text);
    aes_clear_new_message(&aes_instance);
    /* Wait for the end of the encryption process. */
    while (!(aes_get_status(&aes_instance) & AES_ENCRYPTION_COMPLETE)) {
    }
    aes_read_output_data(&aes_instance,output_data);

    if ((ref_cipher_text_ecb[0] != output_data[0]) ||
            (ref_cipher_text_ecb[1] != output_data[1]) ||
            (ref_cipher_text_ecb[2] != output_data[2]) ||
            (ref_cipher_text_ecb[3] != output_data[3])) {
        printf("\r\nKO!!!\r\n");
    } else {
        printf("\r\nOK!!!\r\n");
    }
    printf("\r\n-----------------------------------\r\n");
    printf("- 128bit cryptographic key\r\n");
    printf("- ECB decipher mode\r\n");
    printf("- Auto start mode\r\n");
    printf("- 4 32bit words\r\n");
    printf("-----------------------------------\r\n");


    state = false;

    /* Configure the AES. */
    g_aes_cfg.encrypt_mode = AES_DECRYPTION;
    g_aes_cfg.key_size = AES_KEY_SIZE_128;
    g_aes_cfg.start_mode = AES_AUTO_START;
    g_aes_cfg.opmode = AES_ECB_MODE;
    g_aes_cfg.cfb_size = AES_CFB_SIZE_128;
    g_aes_cfg.lod = false;
    aes_set_config(&aes_instance,AES, &g_aes_cfg);

    /* Set the cryptographic key. */
    aes_write_key(&aes_instance, key128);

    /* The initialization vector is not used by the ECB cipher mode. */

    /* Write the data to be deciphered to the input data registers. */
    aes_write_input_data(&aes_instance, ref_cipher_text_ecb);

    /* Wait for the end of the decryption process. */
    while (!(aes_get_status(&aes_instance) & AES_ENCRYPTION_COMPLETE)) {
    }
    aes_read_output_data(&aes_instance,output_data);

    /* check the result. */
    if ((ref_plain_text[0] != output_data[0]) ||
            (ref_plain_text[1] != output_data[1]) ||
            (ref_plain_text[2] != output_data[2]) ||
            (ref_plain_text[3] != output_data[3])) {
        printf("\r\nKO!!!\r\n");
    } else {
        printf("\r\nOK!!!\r\n");
    }

}

Add to user application initialization (typically the start of main()):

    /* Initialize the system and console*/
    system_init();
    configure_usart();

    aes_get_config_defaults(&g_aes_cfg);

    aes_init(&aes_instance,AES, &g_aes_cfg);
    aes_enable(&aes_instance);

Workflow

1. Define sample data from NIST-800-38A appendix F for ECB mode.

   #define AES_EXAMPLE_REFBUF_SIZE 4
   
   /* @{ */
   uint32_t ref_plain_text[AES_EXAMPLE_REFBUF_SIZE] = {
       0xe2bec16b,
       0x969f402e,
       0x117e3de9,
       0x2a179373
   };
   
   uint32_t ref_cipher_text_ecb[AES_EXAMPLE_REFBUF_SIZE] = {
       0xb47bd73a,
       0x60367a0d,
       0xf3ca9ea8,
       0x97ef6624
   };
   
   const uint32_t key128[4] = {
       0x16157e2b,
       0xa6d2ae28,
       0x8815f7ab,
       0x3c4fcf09
   };
   /* @} */

2. Create related module variable and software instance structure.

   /* Output data array */
   static uint32_t output_data[AES_EXAMPLE_REFBUF_SIZE];
   
   /* State indicate */
   volatile bool state = false;
   /* AES configuration */
   struct aes_config g_aes_cfg;
   /* AES instance*/
   struct aes_module aes_instance;
   struct usart_module usart_instance;

3. Configure, initialize, and enable AES module.
   1. Configuration AES struct, which can be filled out to adjust the configuration of a physical AES peripheral.

          aes_get_config_defaults(&g_aes_cfg);

   2. Initialize the AES configuration struct with the module's default values.

          aes_init(&aes_instance,AES, &g_aes_cfg);

   3. Enable the AES module.

          aes_enable(&aes_instance);

Use Case

Code

Copy-paste the following code to your user application:

    /* Run ECB mode test*/
    ecb_mode_test();

Workflow

1. Configure ECB mode encryption and run test.

   
       state = false;
   
       /* Configure the AES. */
       g_aes_cfg.encrypt_mode = AES_ENCRYPTION;
       g_aes_cfg.key_size = AES_KEY_SIZE_128;
       g_aes_cfg.start_mode = AES_AUTO_START;
       g_aes_cfg.opmode = AES_ECB_MODE;
       g_aes_cfg.cfb_size = AES_CFB_SIZE_128;
       g_aes_cfg.lod = false;
       aes_set_config(&aes_instance,AES, &g_aes_cfg);
   
       /* Set the cryptographic key. */
       aes_write_key(&aes_instance, key128);
   
       /* The initialization vector is not used by the ECB cipher mode. */
   
       aes_set_new_message(&aes_instance);
       /* Write the data to be ciphered to the input data registers. */
       aes_write_input_data(&aes_instance, ref_plain_text);
       aes_clear_new_message(&aes_instance);
       /* Wait for the end of the encryption process. */
       while (!(aes_get_status(&aes_instance) & AES_ENCRYPTION_COMPLETE)) {
       }
       aes_read_output_data(&aes_instance,output_data);
   
       if ((ref_cipher_text_ecb[0] != output_data[0]) ||
               (ref_cipher_text_ecb[1] != output_data[1]) ||
               (ref_cipher_text_ecb[2] != output_data[2]) ||
               (ref_cipher_text_ecb[3] != output_data[3])) {
           printf("\r\nKO!!!\r\n");
       } else {
           printf("\r\nOK!!!\r\n");
       }

2. Configure ECB mode decryption and run test.

   
       state = false;
   
       /* Configure the AES. */
       g_aes_cfg.encrypt_mode = AES_DECRYPTION;
       g_aes_cfg.key_size = AES_KEY_SIZE_128;
       g_aes_cfg.start_mode = AES_AUTO_START;
       g_aes_cfg.opmode = AES_ECB_MODE;
       g_aes_cfg.cfb_size = AES_CFB_SIZE_128;
       g_aes_cfg.lod = false;
       aes_set_config(&aes_instance,AES, &g_aes_cfg);
   
       /* Set the cryptographic key. */
       aes_write_key(&aes_instance, key128);
   
       /* The initialization vector is not used by the ECB cipher mode. */
   
       /* Write the data to be deciphered to the input data registers. */
       aes_write_input_data(&aes_instance, ref_cipher_text_ecb);
   
       /* Wait for the end of the decryption process. */
       while (!(aes_get_status(&aes_instance) & AES_ENCRYPTION_COMPLETE)) {
       }
       aes_read_output_data(&aes_instance,output_data);
   
       /* check the result. */
       if ((ref_plain_text[0] != output_data[0]) ||
               (ref_plain_text[1] != output_data[1]) ||
               (ref_plain_text[2] != output_data[2]) ||
               (ref_plain_text[3] != output_data[3])) {
           printf("\r\nKO!!!\r\n");
       } else {
           printf("\r\nOK!!!\r\n");
       }