I thought this might be of interest for the list, but haven't seen it mentioned/discussed here: Some progress has been made reverse-engineering the Skype protocol [1]. No details on the crypto implementation yet, but first attempts to understand the P2P model they use. Cheers, Ralf [1] S. A. Baset and H. Schulzrinne An Analysis of the Skype Peer-to-Peer Internel Telephony Protocol http://arxiv.org/pdf/cs.NI/0412017 [2] H.T. Kung: CS143: Computer Networks (P2P VoIP) http://www.eecs.harvard.edu/cs143/slides/2004-12-02-p2p-voip.pdf