Function cbc_mac_start

freebsd/crypto/aesni/aesni_ccm.c:88–178

* Start the CBC-MAC process. This handles the auth data. */

 * Start the CBC-MAC process.  This handles the auth data.
 */
static __m128i
cbc_mac_start(const unsigned char *auth_data, size_t auth_len,
	     const unsigned char *nonce, size_t nonce_len,
	     const unsigned char *key, int nr,
	     size_t data_len, size_t tag_len)
{
	__m128i cbc_block, staging_block;
	uint8_t *byte_ptr;
	/* This defines where the message length goes */
	int L = sizeof(__m128i) - 1 - nonce_len;

	/*
	 * Set up B0 here.  This has the flags byte,
	 * followed by the nonce, followed by the
	 * length of the message.
	 */
	cbc_block = _mm_setzero_si128();
	byte_ptr = (uint8_t*)&cbc_block;
	byte_ptr[0] = ((auth_len > 0) ? 1 : 0) * 64 |
		(((tag_len - 2) / 2) * 8) |
		(L - 1);
	bcopy(nonce, byte_ptr + 1, nonce_len);
	append_int(data_len, &cbc_block, L+1);
	cbc_block = AESNI_ENC(cbc_block, key, nr);

	if (auth_len != 0) {
		/*
		 * We need to start by appending the length descriptor.
		 */
		uint32_t auth_amt;
		size_t copy_amt;
		const uint8_t *auth_ptr = auth_data;

		staging_block = _mm_setzero_si128();

		/*
		 * The current OCF calling convention means that
		 * there can never be more than 4g of authentication
		 * data, so we don't handle the 0xffff case.
		 */
		KASSERT(auth_len < (1ULL << 32),
		    ("%s: auth_len (%zu) larger than 4GB",
			__FUNCTION__, auth_len));

		if (auth_len < ((1 << 16) - (1 << 8))) {
			/*
			 * If the auth data length is less than
			 * 0xff00, we don't need to encode a length
			 * specifier, just the length of the auth
			 * data.
			 */
			be16enc(&staging_block, auth_len);
			auth_amt = 2;
		} else if (auth_len < (1ULL << 32)) {
			/*
			 * Two bytes for the length prefix, and then
			 * four bytes for the length.  This makes a total
			 * of 6 bytes to describe the auth data length.