Use crypto. Not too confusing. Mostly asymmetric.
A little ways back, Gunnar Peterson said “passwords are like hamburgers, taste great but kill us in long run wean off password now or colonoscopy later.” I responded: “Use crypto. Not too confusing. Mostly asymmetric.” I’d like to expand on that a little. Not quite so much as Michael Pollan, but a little.
The first sentence, “use crypto” is a simple one. It means more security requires getting away from sending strings as a way to authenticate people at a distance. This applies (obviously) to passwords, but also to SSNs, mother’s “maiden” names, your first car, and will apply to biometrics. Sending a string which represents an image of a fingerprint is no harder to fake than sending a password. Stronger authenticators will need to involve an algorithm and a key.
The second, “not too confusing” is a little more subtle, because there are layers of confusing. There’s developer confusion as the system is implemented, adding pieces, like captchas, without a threat model. There’s user confusion as to what program popped that demand for credentials, what site they’re connecting to, or what password they’re supposed to use. There’s also confusion about what makes a good password when one site demands no fewer than 10 characters and another insists on no more. But regardless, it’s essential that a a strong authentication system be understood by at least 99% of its users, and that the authentication is either mutual or resistant to replay, reflection and man-in-the-middle attacks. In this, “TOFU” is better than PKI. I prefer to call TOFO “persistence” or “key persistence” This is in keeping with Pollan’s belief that things with names are better than things with acronyms.
Finally, “mostly asymmetric.” There are three main building blocks in crypto. They are one way functions, symmetric and asymmetric ciphers. Asymmetric systems are those with two mathematically related keys, only one of which is kept secret. These are better because forgery attacks are harder; because only one party holds a given key. (Systems that use one way functions can also deliver this property.) There are a few reasons to avoid asymmetric ciphers, mostly having to do with the compute capabilities of really small devices like a smartcard or very power limited devices like pacemakers.
So there you have it: Use crypto. Not too confusing. Mostly asymmetric.