Back in the day, Douglas and I were speculating about password replacements (!) We ended up thinking about physical tokens that could be embedded in, say, jewelry, that could be used to authenticate you to some computer system the background, without you explicitly doing anything. Now, there’s Token, about to go mainstream (http://tokenring.com)

Another idea that we dreamed up was that of using the entire history of a person’s interaction with the web, hashed, as a way of proving who they were. Only a person who had a history of the same interactions, all performed in the same sequence over the same time, would be able to authenticate as you. And I’m reading about exactly that in a sci-fi book at the moment, The Fall, by Neal Stephenson. He calls it PURDAH, “Personal Unseperable Registered Designator for Anonymous Holography”.