On his blog, Drummond Reed riffs on some comments I recently made on the OpenID General mailing list concerning the persistence of identity. The upshot is that we should be more aware of the attribute "persistence" when discussing identity systems. This is particularly true when identity systems are intended to model "numerical identity" -- normally assumed to persist -- rather than the often more plastic attributes of qualitative identity.
To better illustrate the issues in this discussion, I propose that we update the well-known "Zooko's Triangle" and create a "Pyramid" that adds the attribute "persistence" to the attributes "Memorable," "Secure," and "Global" which are already included in Zooko's Triangle.
The argument made by Zooko's Triangle is that no naming/identity scheme can provide all three of the attributes Zooko considers essential metrics of identity systems. For instance, while you might be able to build a "Secure and Global" naming system, in doing so, you would undoubtedly need to use identifiers that were not "memorable" -- at least not by mere humans. The importance of these three system attributes and the difficulty of producing systems which provide all three is generally well accepted by those in the naming/identity business.
To the three attributes or axes of Zooko's Triangle, we need to add a fourth axis or dimension which is "Persistence" (i.e. that which relates to the difficult and controversial subject of Identity over Time). The result is a pyramid which allows us to better model constraints on the universe of achievable identity systems. For any of the three traditionally recognized attributes, we need to ask the question "For how long?" (e.g. For how long will an identifier be memorable? For how long will an identity system be secure? What determines the period of time during which a globally unique identifier can be considered "global?")
When Snow White met the dwarfs, the names "Sneezy," "Sleepy", and "Dopey" were highly memorable because those names were highly descriptive of the individuals identified by those names and because those individuals were constantly reinforcing the appropriateness of their names through very visible patterns of behavior. But, had Sneezy recovered from his allergies before meeting Snow White and had Sleepy previously learned to go to bed earlier, Snow White might have found their once memorable names to be less than memorable. (The memorability of the drawf's names was limited to a specific period of time.) Similarly, we are all well aware that we simply don't have the algorithms needed to build systems whose security is everlasting. Security is a temporal quality. No matter how "secure" you may intend your system to be, it is simply a matter of time and effort that is needed to break it.
Perhaps I try to put too much into the picture by using the circle in the middle to show that the degree of persistence is always clipped at some degree less than perfect and everlasting. But, I think it is a very important point to be made and one worth emphasizing. Limits in our mathematical techniques constrain the term of the security and memorability of identities. Among other factors, limits in our ability to ensure that people "follow the rules" constrain how long our solutions may remain global. No solution is everlasting, although for any given purpose, we may be able to build a system which offers sufficient persistence to satisfy our needs.
Drummond Reed closes his blog entry by saying:
Mark my words as we head into 2007 (which I’ve already heard predicted as “the year of OpenID”): the need to use persistent identifiers to provide long-term Internet identity protection will finally start getting the attention it deserves.
I hope the pyramid shown above is a useful contribution to the discussion that Drummond predicts. If nothing else, this model should encourage us to avoid spending too much time trying to create "everlasting" identities and focus instead on designing and deploying systems that provide identities that are merely "usefully" persistent.