bug#11267: bug#15057: 24.3.50; TLS error with reasonably high gnutls-min-prime-bits, bug#11267: 24.0.95; gnutls.c: [0] (Emacs) fatal error: The Diffie-Hellman prime sent by the server is not acceptable (not long enough).

[Roland Winkler]

On Tue Feb 11 2014 Ted Zlatanov wrote:
> So my proposal is simply to provide two buttons "allow host X to
> connect with lower DHE security [temporarily] [permanently]" and
> when the button is clicked, customize `gnutls-algorithm-priority'
> to allow DHE to that specific host.
> 
> `gnutls-negotiate' has to be changed slightly and the connection
> rejection from insecure hosts will need to be handled in gnutls.c
> and gnutls.el.
> 
> I think that's as seamless as we can make it, especially noting
> that `gnutls-min-prime-bits' is deprecated since GnuTLS 3.1.7 (see
> http://www.gnutls.org/manual/gnutls.html#index-gnutls_005fdh_005fset_005fprime_005fbits).
> 
> If we provide that simple UI, plus some help messaging, I think we
> can disable DHE by default.  Based on Nikos' explanation, it seems
> to be the best way forward.

Whatever customizability will be provided (permanently or
temporarily on the fly), I'd find it most important to have
documentation that allows the user to put the choices into
perspective. -- Is this feasible?  Certainly, we cannot expect that
the average user who is offered a pop-up menu with choices "allow
host X to connect with lower DHE security [temporarily]
[permanently]" that he can readily understand its implications and
put it into perspective. (DHE security lower than what?  Lower by
how much?  How insecure is that?)

(According to Murphy's law, this selection will probably pop up most
often, when the user is not in the mood to read long info pages...)

Roland