4.6 Parameters Stored in Credentials
Several parameters such as the ones used for Diffie-Hellman
authentication are stored within the credentials structures, so all
sessions can access them. Those parameters are stored in structures
such as gnutls_dh_params_t and gnutls_rsa_params_t, and
functions like gnutls_certificate_set_dh_params and
gnutls_certificate_set_rsa_export_params can be used to
associate those parameters with the given credentials structure.
Since those parameters need to be renewed from time to time and a
global structure such as the credentials, may not be easy to modify
since it is accessible by all sessions, an alternative interface is
available using a callback function. This can be set using the
gnutls_certificate_set_params_function. An example is shown
below.
| | #include <gnutls.h>
gnutls_rsa_params_t rsa_params;
gnutls_dh_params_t dh_params;
/* This function will be called once a session requests DH
* or RSA parameters. The parameters returned (if any) will
* be used for the first handshake only.
*/
static int get_params( gnutls_session_t session,
gnutls_params_type_t type,
gnutls_params_st *st)
{
if (type == GNUTLS_PARAMS_RSA_EXPORT)
st->params.rsa_export = rsa_params;
else if (type == GNUTLS_PARAMS_DH)
st->params.dh = dh_params;
else return -1;
st->type = type;
/* do not deinitialize those parameters.
*/
st->deinit = 0;
return 0;
}
int main()
{
gnutls_certificate_credentials_t cert_cred;
initialize_params();
/* ...
*/
gnutls_certificate_set_params_function( cert_cred, get_params);
}
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