@deftypefun {int} {gnutls_dh_get_prime_bits} (gnutls_session_t @var{session})
@var{session}: is a gnutls session

This function will return the bits of the prime used in the last
Diffie-Hellman key exchange with the peer.  Should be used for both
anonymous and ephemeral Diffie-Hellman.  Note that some ciphers,
like RSA and DSA without DHE, do not use a Diffie-Hellman key
exchange, and then this function will return 0.

@strong{Returns:} The Diffie-Hellman bit strength is returned, or 0 if no
Diffie-Hellman key exchange was done, or a negative error code on
failure.
@end deftypefun