full-disclosure - blocking SkyPE?

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Message-ID: <20050124085744.GC26105@ait.ac.th>
From: alain at ait.ac.th (Alain Fauconnet)
Subject: blocking SkyPE?

Hello list,

This may be a bit borderline topic. Feel free to redirect me to a more
appropriate place for this discussion if you know one.

I need to block SkyPE at the border of our network for many reasons.
It's not an easy task. The following paper:

http://www1.cs.columbia.edu/~library/TR-repository/reports/reports-2004/cucs-039-04.pdf

gives a lot of insight to the protocol. This stuff has been obviously
engineered to bypass any port-based or IP-based blocks and L7 protocol
identification. The folks of L7-filter have a pattern at
http://l7-filter.sourceforge.net/layer7-protocols/protocols/skype.pat
but it's classified as having 'marginal' effectiveness.

Based on the paper mentioned above, the weak point might be the direct
connection to the SkyPE login servers, but in my observation, login
process seems to possibly take place through supernodes as well in
recent versions.

Has anyone worked on this? Googling doesn't return much useful.

Greets,
_Alain_