@deftypefun {int} {gnutls_x509_ext_export_subject_key_id} (const gnutls_datum_t * @var{id}, gnutls_datum_t * @var{ext})
@var{id}: The key identifier

@var{ext}: The DER-encoded extension data; must be freed using @code{gnutls_free()} .

This function will convert the provided key identifier to a
DER-encoded PKIX SubjectKeyIdentifier extension. 
The output data in  @code{ext} will be allocated using
@code{gnutls_malloc()} .

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned, otherwise a negative error value.

@strong{Since:} 3.3.0
@end deftypefun