Re: A couple of questions and concerns about Emacs network security

[Stephen Berman <stephen.berman@gmx.net>]

On Fri, 06 Jul 2018 11:49:45 +0300 Eli Zaretskii <eliz@gnu.org> wrote:

>> From: Robert Pluim <rpluim@gmail.com>
>> Cc: "Perry E. Metzger" <perry@piermont.com>, larsi@gnus.org,
>> eggert@cs.ucla.edu, emacs-devel@gnu.org, npostavs@gmail.com,
>> wyuenho@gmail.com
>> Date: Fri, 06 Jul 2018 10:36:54 +0200
>> 
>> > Anyway, it seems you completely miss my point: I didn't say that we
>> > shouldn't increase the number of bits, just that we shouldn't do that
>> > on the release branch, unless we are willing to delay Emacs 26.2
>> > significantly.
>> 
>> FWIW, Iʼve had gnutls-min-prime-bits set to 1024 since 2014-11-25, and
>> have seen no adverse effects from it, so I donʼt think the risk is
>> that great.
>
> Thanks for the data point.
>
> Unfortunately, our experience is that use patterns vary widely between
> different Emacs users, and so problem-free experience of a single
> individual, or even several people, is not enough to be sure there are
> no significant issues.  And TLS secured connections are central to
> many Emacs features.
>
> Emacs 26.2 is supposed to have fewer significant bugs than Emacs 26.1,
> so we must be careful if we make changes that could bring new
> problems.

I think in this case it is likely that the higher setting has in effect
already undergone prolongued testing, since there is reason to think it
has been used by many, perhaps most, Emacs users for a long time, in my
case since reading this posting:

  From: "Herbert J. Skuhra" <hskuhra@eumx.net>
  Subject: Re: gnutls.c warning
  Newsgroups: gmane.emacs.gnus.general
  To: david@adboyd.com (J. David Boyd)
  Cc: ding@gnus.org
  Date: Tue, 25 Jun 2013 23:38:14 +0200 (5 years, 1 week, 3 days ago)
  
  On Tue, 25 Jun 2013 15:07:08 -0400
  david@adboyd.com (J. David Boyd) wrote:
  
  > 
  > I keep getting this warning, and can't find any way to turn it off.
  > 
  > gnutls.c: [1] Note that the security level of the Diffie-Hellman key
  > exchange has been lowered to 256 bits and this may allow decryption
  > of the session data
  >  
  > Is there some setting to say ok, I understand, quit nagging me?
  
  After setting gnutls-min-prime-bits to 1024 I no longer get this
  warning.

Given this, it seems reasonable to conclude that most Emacs users who
continue to use the current default setting are aware of the risk, and
those who have changed it haven't experienced a problem worth reporting.
Therefore, changing the default at this time is not likely to cause a
problem for most long-time users, and will be safer for all new users,
and most likely unproblematic for them (and if it is a problem, then
they will know the trade-off).

Steve Berman