An authentication family tree

How do we make best sense of the bewildering array of authenticators on the market? Most people are familiar with single factor versus two factor, but this simple dichotomy doesn’t help match technologies to applications. The reality is more complex. A family tree like the one sketched here may help navigate the complexity.

Different distinctions define various branch points. The first split is between what I call Transient authentication (i.e. access control) which tells if a user is allowed to get at a resource or not, and Persistent authentication, which lets a user leave a lasting mark (i.e. signature) on what they do, such as binding electronic transactions.

Working our way up the Transient branch, we see that most access controls are based either on shared secrets or biometrics. Dynamic shared secrets change with every session, either in a series of one time passwords or via challenge-response.

On the biometric branch, we should distinguish those traits that can be left behind inadvertently in the environment and are more readily stolen. The safer biometrics are “clean” and leave no residue. Note that while the voice might be recorded without the speaker’s knowledge, I don’t see it as a residual biometric in practice because voice recognition solutions usually use dynamic phrases that resist replay.

For persistent authentication, the only practical option today is PKI and digital signatures, technology which is available in an increasingly wide range of forms. Embedded certificates are commonplace in smartcards, cell phones, and other devices.

The folliage in the family tree indicates which technologies I believe will continue to thrive, and which seem more likely to be dead-ends.

I’d appreciate feedback. Is this useful? Does anyone know of other taxonomies?