SSL client side certificates are already implemented, but they have their own problems: 1) UI is hard to use http://pilif.github.com/2008/05/why-is-nobody-usin

SSL client side certificates are already implemented, but they have their own problems: 1) UI is hard to use http://pilif.github.com/2008/05/why-is-nobody-using-ssl-client-certificates/ http://pilif.github.com/2008/05/why-is-nobody-using-ssl-clie... 2) Can be easily stolen by malware (if client certificate is password-protected then password can be locally bruteforced on attacker's system) 3) It's not easy to switch identities (if you have multiple accounts on some website). And whenever there is no support for multiple identities, there is a ground for privacy concerns. 4) It's almost impossible to enter them from keyboard. How do I enter one on the iPhone? How do I write it on paper? What if I need to access some website from work and from home? What if my USB thumbdrive with client SSL certs fails or gets stolen? 5) They expire eventually, and when they do, users have another out-of-common-sense problem to solve. So, implementation already exists but it's impractical.