@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