@deftypefun {int} {gnutls_hmac_init} (gnutls_hmac_hd_t * @var{dig}, gnutls_mac_algorithm_t @var{algorithm}, const void * @var{key}, size_t @var{keylen})

@var{dig}: is a @code{gnutls_hmac_hd_t}  type

@var{algorithm}: the HMAC algorithm to use

@var{key}: the key to be used for encryption

@var{keylen}: the length of the key

This function will initialize an context that can be used to

produce a Message Authentication Code (MAC) of data.  This will

effectively use the current crypto backend in use by gnutls or the

cryptographic accelerator in use.

Note that despite the name of this function, it can be used

for other MAC algorithms than HMAC.

@strong{Returns:} Zero or a negative error code on error.

@strong{Since:} 2.10.0

@end deftypefun