Crypto

RIOT provides a collection of block cipher ciphers, different operation modes and cryptographic hash algorithms.

Ciphers

Riot supports the following block ciphers:

  • AES-128
  • NULL

You can use them directly by adding “crypto” to your USEMODULE-List. While you can use the ciphers functions directly, you should resort to the generic API for block ciphers whenever possible.

Additionally you need to set a CFLAG for each cipher you want to use in your Makefile:

  • AES-128: CFLAGS += -DCRYPTO_AES Setting the CFLAGS initializes a sufficient large buffer size of the cipher_context_t, used by the ciphers for en-/de-cryption operations.

Example: 

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#include "crypto/ciphers.h"

cipher_t cipher;
uint8_t key[AES_KEY_SIZE] = {0},
        plain_text[AES_BLOCK_SIZE] = {0},
        cipher_text[AES_BLOCK_SIZE] = {0};

if (cipher_init(&cipher, CIPHER_AES_128, key, AES_KEY_SIZE) < 0)
    printf("Cipher init failed!\n");

if (cipher_encrypt(&cipher, plain_text, cipher_text) < 0)
    printf("Cipher encryption failed!\n");
else
    od_hex_dump(cipher_text, AES_BLOCK_SIZE, 0);

Some aspects of the AES implementation can be fine tuned by pseudo-modules:

  • crypto_aes_precalculated: Use pre-calculated T-tables. This improved speed at the expense of increased program size. The default is to calculate most tables on the fly.
  • crypto_aes_unroll: enable manually-unrolled loops. The default is to not have them unrolled.

If you need to encrypt data of arbitrary size take a look at the different operation modes like: CBC, CTR or CCM.

Additional examples can be found in the test suite.