Smart Cookies The Unstealable Authentication Cookie

The web has become a new, highly interactive medium. Many modern websites provide their users with the opportunity to alter their content in some way. This trend is especially evident in Wikis, where users are encouraged to collaboratively edit pages if they have something to add. Blogs and online forums are another example of sites which encourage their readers to contribute content. Finally, web-based e-mail providers such as GMail and Yahoo can be considered collaborative web-pages in some respects, as ordinary end-users are able to directly influence the content that is rendered on the mailbox owner’s browser. The collaborative web has made a large number new applications possible. However, like many other advances in Internet development, it has also cre-ated a number of security issues, including “cross-site cooking”. This attack, itself a special case of “cross-site scripting”, allows a malicious user to re-trieve cookies from another user’s browser set by a domain the he does not control. In order to capture the cookies, the attacker simply has to ensure that his script is rendered by the client’s browser when he visits the domain for which the cookies are desired. The attack does not involve exploiting a bug in the user’s browser; in fact, the attack can be as simple as the one shown in Figure 1. Since websites will frequently accept a cookie containing a session ID as proof that the user is authenticated, this attack al-lows a malicious user to gain unauthorized access to a service. An obvious fix would be to require interactive web-sites to carefully escape all user-provided content so that client browsers do not execute untrusted scripts. However, even though many popular web program-<a href="# " onclick="window.location