[Operators] xmpp.net is back and some logjam stats

Thijs Alkemade thijs at xnyhps.nl
Thu Oct 22 09:09:39 UTC 2015

Hello all,

As discussed previouson this list, xmpp.net was down for a while due to
hardware failure. It is now back up on a different server. Most of it is
working again, but some tables on the stats page are still broken.

While doing that, I also made some updates to the test, inspired by the
updates to ssllabs.com:

* Grades will be capped to B if SSLv3 is supported. The grade will be F if
  SSLv3 is the highest protocol version supported.

* Grades will be capped to C if RC4 is used with TLS 1.1 or TLS 1.2.

* The size of the DH parameters now impacts the key exchange score.

* Grades will be capped to B when using DH parameters of less than 2048 bits.

* Grades will be capped to C if TLS compression is enabled.

* Grades will be capped to C when TLS 1.2 is not supported.

Additionally, the DHE group and the ECDHE curve that were used are now stored,
to see how much the Logjam attack [1] impacts XMPP servers.

With just a couple of days of data, here's some statistics on the standard DH
groups used:

 count |                           group_name
     1 | RFC 3526 3072-bit MODP Group
     1 | RFC 3526 4069-bit MODP Group
     1 | draft-ietf-tls-negotiated-ff-dhe-10 ffdhe2048
     1 | RFC 2409 Second Oakley Group
     1 | RFC 3526 8192-bit MODP Group
    12 | RFC 3526 2048-bit MODP Group
    14 | Java sun.security.provider default 512-bit prime
    22 | Java sun.security.provider default 1024-bit prime
    60 | Java sun.security.provider default 768-bit prime
   131 |
   157 | RFC 5114 1024-bit MODP Group with 160-bit Prime Order Subgroup

This means only 131 of these 410 servers are using custom DH parameters. 60
servers are using a common 768-bit DH group and 14 servers using a common
512-bit prime (which are likely using DHE-EXPORT, so vulnerable to logjam).

[1] estimates that breaking a 768-bit prime is within reach for an academic
team. The version replies from the servers using the 768-bit prime indicates
they are running Openfire 3.7 - 3.10 or Tigase 5.2.1. All other Openfire
servers are using the Java sun.security.provider default 1024-bit prime
(probably the difference between Java 7 and Java 8).

[1] further estimates that breaking a few commonly used 1024-bit groups would
be in range for a nation-state attacker and the RFC 5114 1024-bit MODP Group
is used a lot. Version replies show these servers are running ejabberd 2.1 -

It appears ejabberd 15.06 added an option to set your own dh parameters [2], I
strongly recommended to upgrade and generate your own parameters. If you are
running Openfire (or are using ejabberd and unable to update), you might want
to disable DHE completely and rely on ECDHE instead.

[1] = https://weakdh.org/
[2] = https://www.ejabberd.im/node/24959

Best regards,

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