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[ISN] German police Skype-hacking leaked


By John E. Dunn
28 January 2008

German police have hired a company to create Trojans capable of 
capturing traffic from Skype and SSL, leaked documents appear to show.

The two scanned documents [1], which appear on the Wikileaks website in 
their German form, are difficult to verify, but one appears to describe 
how a security company, Digitask, was asked to create a Skype Capture 
Unit based around Trojans planted on targeted PCs covertly transferring 
data to a remote server.

As requested by you, we hereby submit an offer for a surveillance method 
of the encrypted VoIP protocol Skype, says the company hired to carry 
out the hacking.

The other document relates to an apparent exchange between the Bavarian 
police, the Ministry of Justice and the Prosecution office, on how to 
divide up the costs of this system. According to Wikileaks, this 
originally appeared on German website Piratenpartei, but was removed, 
speculating that this could be due to legal threats.

The description of the Skype Capture Unit is dated September 4, 2007 
with a delivery timescale for a targeted system in weeks, implying that 
the system could have been operational for some time.

The precise capabilities of the system are hard to gauge, but its 
creators appear confident of being able to capture Skype's voice, chat 
and video sessions, and possibly also hacking SSL. Since both are 
encrypted, it is likely that the data streams are first copied to remote 
servers first before being decrypted once the key used to scramble them 
has been recovered.

Encryption of communication via Skype poses a problem for surveillance 
of telecommunications. All traffic generated by Skype can be captured 
when surveilling a Dial-in- or DSL link, but it cannot be decrypted. The 
encryption of Skype works via AES wih a 256-Bit key. The symmetric AES 
keys are negotiated via RSA keys . The public keys of the users are 
confirmed by the Skype-Login-Server when logging in. To surveil 
Skype-communication it thus becomes necessary to realize other 
approaches than standard telecommunications surveillance, the document 

How Digitask intended to get the Trojans on to targeted PCs without 
breaking German law is not explained.

This is no cheap hack for nosy policemen each successfully compromised 
machine would net Digitask 3,500 euros per month for at least three 
months. SSL interception is said to cost 2,500 euros.

The interest German authorities have in hacking Skype has known about 
for some time. In November 2007 after the time period covered by leaked 
documents a source in the German police suggested that they had been 
unable [2] to crack Skypes encryption.

Unencrypted VoIP calls are a very different matter. Also in November, 
VoIP expert Peter Cox created a VoIP-hacking proof-of-concept program 
called SIPtap [3], which does exactly what the Skype Capture Unit claims 
to do, minus the ability to do this for encrypted Skype calls.

[1] http://wikileaks.org/wiki/Skype_and_the_Bavarian_trojan_in_the_middle
[2] http://www.techworld.com/mobility/news/index.cfm?newsid=10751
[3] http://www.techworld.com/security/news/index.cfm?newsID=10736

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