Between your comments, brl's, and the JSF paper, its clear enough how this works now. Thanks. I still suspect this is being overhyped. Being able to forge the

Between your comments, brl's, and the JSF paper, its clear enough how this works now. Thanks. I still suspect this is being overhyped. Being able to forge the auth cookie 100% of the time doesn't change the fact that you need a server-recognized value to actually forge. This seems like it could indeed badly damage apps that stash important things in client state expecting it to be secure, but a lot of bog standard asp.net apps will be unscathed, unless I'm missing some killer detail. We'll see. Edit: If the contents of a forms authentication cookie are not session-bound and assume that crypto == safe, that could certainly make things interesting. No idea though. Edit2: Increasingly convinced that this could enable devastating attacks on forms auth (a large proportion of asp.net apps to be sure) - the content of a forms auth ticket appears to be trivially constructed.