Risks of the Passport single signon protocol

Passport is a protocol that enables users to sign onto many different merchants' Web pages by authenticating themselves only once to a common server. This is important because users tend to pick poor (guessable) user names and passwords and to repeat them at different sites. Passport is notable as it is being very widely deployed by Microsoft. At the time of this writing, Passport boasts 40 million consumers and more than 400 authentications per second on average. We examine the Passport single signon protocol, and identify several risks and attacks. We discuss a flaw that we discovered in the interaction of Passport and Netscape browsers that leaves a user logged in while informing him that he has successfully logged out. Finally, we suggest several areas of improvement. (C) 2000 Published by Elsevier Science B.V. All rights reserved.