int tc_ctr_mode()

in ext/tinycrypt/src/ctr_mode.c [37:85]

• 37 lines of code
• 11 McCabe index (conditional complexity)

int tc_ctr_mode(uint8_t *out, unsigned int outlen, const uint8_t *in,
		unsigned int inlen, uint8_t *ctr, const TCAesKeySched_t sched)
{

	uint8_t buffer[TC_AES_BLOCK_SIZE];
	uint8_t nonce[TC_AES_BLOCK_SIZE];
	unsigned int block_num;
	unsigned int i;

	/* input sanity check: */
	if (out == (uint8_t *) 0 ||
	    in == (uint8_t *) 0 ||
	    ctr == (uint8_t *) 0 ||
	    sched == (TCAesKeySched_t) 0 ||
	    inlen == 0 ||
	    outlen == 0 ||
	    outlen != inlen) {
		return TC_CRYPTO_FAIL;
	}

	/* copy the ctr to the nonce */
	(void)_copy(nonce, sizeof(nonce), ctr, sizeof(nonce));

	/* select the last 4 bytes of the nonce to be incremented */
	block_num = (nonce[12] << 24) | (nonce[13] << 16) |
		    (nonce[14] << 8) | (nonce[15]);
	for (i = 0; i < inlen; ++i) {
		if ((i % (TC_AES_BLOCK_SIZE)) == 0) {
			/* encrypt data using the current nonce */
			if (tc_aes_encrypt(buffer, nonce, sched)) {
				block_num++;
				nonce[12] = (uint8_t)(block_num >> 24);
				nonce[13] = (uint8_t)(block_num >> 16);
				nonce[14] = (uint8_t)(block_num >> 8);
				nonce[15] = (uint8_t)(block_num);
			} else {
				return TC_CRYPTO_FAIL;
			}
		}
		/* update the output */
		*out++ = buffer[i%(TC_AES_BLOCK_SIZE)] ^ *in++;
	}

	/* update the counter */
	ctr[12] = nonce[12]; ctr[13] = nonce[13];
	ctr[14] = nonce[14]; ctr[15] = nonce[15];

	return TC_CRYPTO_SUCCESS;
}