Category Archives: Cryptography

Skype with a ‘Z’

IP Softphone specialists CounterPath recently announced that they will license Phil Zimmermann’s ZRTP (Zfone) technology for use in their client products, namely eyeBeam and X-Lite, joining other publicly announced licencees Borderware, PGP Corp, Ripcord and TiVi.

As you may know, ZRTP has done very well in terms of acceptance in the last few months. Zimmermann has many friends in the security community, but also has great credentials in the open source world. ZRTP is an openly published protocol, but also is available as source code, thereby making it possible to test in all kinds of ways, not only closed-box (black box) testing but also in terms of working through the algorithm and even unit testing the code.

At the recent IETF meeting, methods of key exchange were discussed, as subscribers to the Voipsec list (from the VOIPSA site) cannot have failed to miss. The IETF have gone from a list of thirteen proposals down to a final two, and ZRTP is one of those, despite being considered by some as a latecomer.  Many organizations and people that I have come across trust in Zimmermann and believe that ZRTP is the answer.

If we go to the opposite end of the trust scale, we find Skype.  Poor old Skype are still getting weekly batterings from press critics on the security front.  A lot of the same criticisms are brought up time and time again, and in fairness Skype have countered a lot of the concerns, by allowing features to be switched off, changes to the package and so on.  We don’t need to rehearse all those issues here once again.

However, the issues that keep coming up, and which Skype have not argued away are those of security by obscurity and the secrecy of the protocols they use for encryption and key exchange. Famously, Skype hired security expert Tom Berson to write a report based on a long evaluation of Skype’s security provisions, but most academics still desire transparency, and the ability to evaluate the algorithms for themselves.

Academics and commercial security experts both say that simply using a secret algorithm is no guarantee of safety. Furthermore, the fact that it is secret merely means that when someone does compromise Skype, the detection and mitigation of the problem will be slowed down or prevented. Skype at that point becomes a dangerous ‘bot’ sitting behind thousands of firewalls.

What better time, then, for Skype to embrace ZRTP? Licensing ZRTP can hardly be a problem for Skype and its Ebay parent, and there is so much to gain from this. A large community of security and VoIP specialists already believe in ZRTP; the IETF likes it; commercial acceptance exists in licencees in the Softphone and Session Border Controller market. IT Managers, I’m sure, would be happier with Skype usage in the workplace if they were allowed to detect and control it, and (who knows with key escrow) in some way to log and record from it.

Come on, Skype, grab the nettle. The tools are in your hands to silence your critics.