[gnutls-dev] Re: ongoing entropy problems

Andreas Metzler ametzler at downhill.at.eu.org
Tue Jan 31 19:30:29 CET 2006

On 2006-01-31 Simon Josefsson <jas at extundo.com> wrote:
> Jason Lunz <lunz at falooley.org> writes:
> > Are the gnutls developers aware of the ongoing entropy-pool-draining
> > problems with gnutls in exim4? For example:

> > http://article.gmane.org/gmane.linux.debian.devel.exim4.user/477

> > Is this a known problem? Can something be done about it?

> We are working on it, please see the other current threads on the
> mailing list.

> I believe we have identified the problem, and proposed a solution, so
> a exim developer could probably implement it.  Any exim developers
> following this?

As far as I gather from reading http://bugs.debian.org/343085 and the
thread "Feature request: not really random session keys" on gnutls-dev
there are two problems.

#1: Online, blocking generation of RSA-params and DH-params in exim.
This is already fixed for quite some time in exim (thanks Nikos
Mavrogiannopoulos), it switched to using a certtool-compatible
fileformat for these parameters and certtool can be used for
generating them offline.

#2: Florian Weimer wrote in http://bugs.debian.org/343085
| As a side note: With GNU TLS, every _single_ encrypted mail
| transmission _totally_ depletes my entropy pool (going from ~3500 to
| ~150), but after recompiling Exim4 with OpenSSL, only about 200 bits
| (the number is difficult to measure, but it is way less than with GNU
| TLS) are used.

For bug #2 /dev/urandom is used, therefore there is no blocking in
exim, just the fact that anything using /dev/random will block, as
there is no entropy left.

The issue Jason is refereing to is #2, which is not fixed /yet/ but
         cu andreas
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