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03 June 2011, 11:52

Skype protocol being reverse engineered - update

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Skype logo A freelance researcher named Efim Bushmanov has created a site named "skype-open-source" and says that he is reverse engineering the VoIP service Skype "to make skype open source". Skype's proprietary protocols have allowed the company to maintain control over its peer-to-peer voice and video communications network and have been the subject of various types of research over the years.

Bushmanov is not taking a clean room approach, where a researcher examines the network inputs and outputs of the software. He has instead opted for the potentially riskier process of modifying the Skype binary files to remove autoupdate, obfuscation and anti-debugging measures. Bushmanov may also be taking a risk by redistributing these modified files; they are easier to decompile and it is easier to trace and log what the code does, but they are still Skype's intellectual property.

Bushmanov is working in part from a 2006 presentation, Vanilla Skype (part 1PDF, part 2PDF), which previously reverse-engineered Skype's client and protocols. He also uses cipher code from VEST Corporation's reverse engineering of Skype. This code is marked "all rights reserved" and "for academic research and educational purposes only". Update - That code was written by Sean O'Neill, who presented his emulation of the modified version of the RC4 encryption code used by Skype last year.

The most recent posting from Bushmanov indicates that he still has much work to do and that the "test code" he has released will only work with Skype 1.4 which cannot successfully connect to the supernodes of the current Skype 5.x network.

Given the process used for reverse engineering and the existence of non-open source code in the code base, it is unlikely that – even if Bushmanov is successful in interacting with the current Skype network – this will lead to an open source implementation of the Skype protocols which meets the open source definition.


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