| Yes, but, if you change your password / answer your security questions to get back in you get control back. Now say they get your Persona email account, and get the signing material from it once. They can now log in everywhere until that material expires. There's nothing you can do about it. THAT is very different. There's a small thing you could do to mitigate this, but really only self-hosted email has it as an option: change the email server's keys. You would be able to block logins to any site which has not cached those keys. But no big provider would do it for you, since it would break everyone's currently-live keys, and from what I can remember they recommend that sites using Persona login cache the keys[1]. So any site you had logged into may very well have cached them, and not even perform a web request, and still allow the malicious login. -- The only real way to dial back this damage is to limit the lifetime of the original signature. Make it too short and slow internet connections can't log in anywhere, and browsers have to continually request new assertion-signing data. Make it too long and you let attackers try many, many, many more sites. [1]: I can't find this on the Persona/BrowserID site :/ maybe it was in a presentation somewhere. Anyway, it's inherently cache-able material, and it is a great selling point - server-side web requests are painfully slow. |
On our internal Persona IdP (for mozilla.com and mozillafoundation.org email addresses), the signature is short-lived (a few minutes I think). The browser will therefore need to request a new signature very often. This can happen transparently as long as you still have a session with the IdP and that session can be invalidated server-side in case of a compromise (or a password change).