GnuTLS/NSS interop in Exim 4.80 RC

[Phil Pennock]

On 2012-05-20 at 16:24 +0200, Nikos Mavrogiannopoulos wrote:
>  From what I can tell it is the client for some reason terminates the
> connection. What is the output on the client? Do you have a tcpdump of
> the issue? Have you tried alternative priority strings than normal
> [0]?

The client is using NSS and from what I can tell does not log problems
at the NSS level.  I've searched for ways to do that but failed.  The
protocol dump email I referenced in the first post includes the output
from ssltap; is that sufficient or do you want a raw packet capture?

> [0]. http://www.gnu.org/software/gnutls/manual/html_node/Interoperability.html

Well, I need to add a new test to the test suite, since I had omitted an
assignment and the default of NORMAL was always being used.

NORMAL:%COMPAT does not help.
NORMAL:-VERS-TLS-ALL:+VERS-TLS1.0:+VERS-SSL3.0:%COMPAT does not help.

NORMAL:-VERS-TLS-ALL:+VERS-TLS1.0:+VERS-SSL3.0:-CIPHER-ALL:+ARCFOUR-128:%COMPAT
*does* work.

With just "NORMAL:-CIPHER-ALL:+ARCFOUR-128" negotiation works and the
negotiated protocol is TLS1.0:RSA_ARCFOUR_MD5:128.  So it's not %COMPAT
that causes issues.

"AEAD" isn't recognised in 2.12.  Looking at the .texi I see that 2.12
supports: AES-128-CBC, AES-256-CBC, CAMELLIA-128-CBC, CAMELLIA-256-CBC,
ARCFOUR-128, 3DES-CBC ARCFOUR-40.

Incrementally adding each of the items listed below in turn, I needed:
  NORMAL:-AES-256-CBC:-CAMELLIA-256-CBC:-CAMELLIA-128-CBC:-AES-128-CBC
go get Thunderbird negotiating.

NORMAL:-AES-128-CBC:-AES-256-CBC is *not* sufficient.
NORMAL:-CAMELLIA-256-CBC:-CAMELLIA-128-CBC is *not* sufficient.

strings(1) on libnss3.dylib shipped with Thunderbird (MacOS) suggests
that it is 3.13.3.0 which is far more recent than anything listed on
<http://www.mozilla.org/projects/security/pki/nss/>.

However, Exim supports both OpenSSL and GnuTLS.  If I use an OpenSSL
Exim, then Thunderbird successfully delivers using
TLSv1:CAMELLIA256-SHA:256.

So it's not Camellia in itself that's the problem.  It's those ciphers
as offered by GnuTLS, as opposed to OpenSSL.

-Phil