SKYPE SECURITY EVALUATION（SKYPE安全评估）.pdfVIP

1 SKYPE SECURITY EVALUATION Tom Berson Anagram Laboratories 18 October 2005 berson@ skype:tomnd2t 1. Introduction and Summary I have been a Skype user since August 2004. My 35-year long career as cryptographer and computer security expert has taught me to be professionally skeptical about the security of almost everything, especially of a system which is as adept as Skype at getting through typical network defenses. So I re-formatted the hard disk on a spare computer and dedicated the box to the Skype application. Over the next few months I monitored the list of processes running on the machine, looking for anything suspicious. I also ran a number of experiments during which I captured and analyzed the packets flowing into and out of the box. I was looking for malicious activity and trying to figure out how Skype works. Perhaps you have run similar experiments yourself. You may imagine my delight when, in April 2005, Skype contacted me and invited me to compete for the job of performing an independent evaluation of Skype information security, with a special focus on the Skype cryptosystem. I traveled to the Skype engineering center in Tallinn, and to the Skype business center in London. In each place I interviewed Skype people and was interviewed by them. The meetings went well; I won the business. Since 1 June 2005 I have been analyzing the security properties of Skype software and services, with a focus on the current and planned uses of cryptography. I have had unimpeded access to Skype engineers and to Skype source code. I have found out a lot about Skype. The more I found out, the happier I became. Skype makes wide use of cr