+
+/* how many bytes will it take to write out this datum in OpenPGP MPI form? */
+size_t get_openpgp_mpi_size(gnutls_datum_t* d);
+
+/* write the MPI stored in gnutls_datum_t to file descriptor fd: */
+int write_openpgp_mpi_to_fd(int fd, gnutls_datum_t* d);