This paper is a study of the Skype protocol. Because Skype protocol is not public, this study provides valuable information. This leak of transparency is against cryptographic security and provide legal and political issues
In particular this paper depict the architecture of the Skype network and help to understand how different it is from MSN or Yahoo messenger. I found the analysis of how Skype evade firewall clear. The only regret I have is that the diagram used in the first version is not present in the current version. It would have be nice to keep it and show the difference between the different versions of the protocol. Among the information reported, let’s note : The selfish behavior of Skype that eat all the resource it can and the fact that Skype does not allow a user to prevent its machine from becoming a super node. This show the darkside of this application.
As a final word I recommend any one who use or plan to use Skype to read this study because it present in a clear way the protocol behavior. The only unclear point left is how Skype generate the AES key used to encrypt its packets. It there a public/private key scheme or is it an IV along with user password ? Hope an other study will answer such question.
Detailed Information about this article (5w-1h report)
What it is
This is a experiment that aims to reverse engineer the Skype protocol. The version used is Windows Skype version 1.4.0.84. Information about the evolution of the protocol are also provided as the first version of the paper was on version 0.9 beta.
Why it is useful
Skype protocol is not public and encrypted, therefore the information provided by this article are valuable to understand how it works. In particular it explains how Skype bypass firewall.
Who write it
Salman A. Baset and Henning Schulzrinne from the computer science department of Columbia University.
Henning Schulzrinne is Professor of the the computer science department of Columbia University and Salman Abdul Baset is one of his Phd Students (2nd year).
Where it will be found
It will appears in IEEE Infocom 2006 and version is available on the authors page
When it was made
A first version of the work was availabe in 2004. The Infocom version was done in 2006.
How the studt was performed
To reverse the protocol , they use three different kinds of set up and a sniffer : Wireshark. They also use a bandwidth shaper (Ether peek) to experiment Skype behavior in low bandwidth context.
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