This play on Salvador Dali’s famous painting “The Persistence of Time” is to point out a principle that seems to recur with every evolutionary step of Internet identity architecture: the fundamental importance of persistent identifiers.

For example, last week on the OpenID General mailing list, I answered a question about the difference between using URLs and XRIs as OpenID identifiers by explaining that URLs, being based on DNS names or IP addresses, have the inherent problem that they are reassignable. As I explained in an earlier post, in an Internet identity architecture like OpenID in which your identifier is the entire key to your identity (because it is resolved to determine the identity provider from which an authentication assertion can be requested), using a reassignable identifier means your entire identity can be “taken over” if the domain name or IP address of your URL is ever reassigned. This would be tantamount to a U.S. citizen having their Social Security Number reassigned to another citizen, but even worse because there would be nothing in the infrastructure at all to prevent this, or even signal that there was something wrong.

I went on to explain:

XRI infrastructure solves this problem by explicitly supporting reassignable identifiers (i-names) and persistent identifiers (i-numbers) and permitting the resolution of any reassignable i-name to be mapped immediately to a synonymous, never-reassigned i-number which can be safely stored by an OpenID Relying Party without exposing the identity owner to the risk of having their i-name “taken over”.

Bob Wyman responded with a very important point:

The XRI Syntax specification says that a Persistent Identifier is “An identifier that is permanently assigned to a resource and intended never to be reassigned to another resource.” While it may well be the “intention” that such persistent identifiers are never to be reassigned, one must accept that an “identity owner” is, in fact, exposed to some risk of having their i-name ‘taken over’” in the case of unintended events. There is nothing technical which prevents the taking over of XRI persistent identifiers. The only thing that reduces risk here is people’s and organization’s willingness and ability to follow the rules. Such trust may well be reasonably held, but there remains an ineradicable risk of entities’ failure to perform as intended… (Note: The previous comments should not be taken as a criticism of XRI. This ‘risk’ is an inevitable characteristic of this class of system and of this type of “solution”.)

So important is Bob’s point that today I replied with the following:

Bob is absolutely right that there is nothing inherent in the technical aspects of XRI architecture — nor was there in the URN (Uniform Resource Name) architecture that came before it – to prevent the reassignment of an identifier intended to be persistent (which both XRI i-numbers and URNs are). Such protection is afforded *entirely* by the operational policies of the authority assigning the identifier, i.e., the registry.Part of the reason URNs did not catch on (besides the fact they are typically very un-human-friendly identifiers) is that the operational requirements of a URN registry are so dramatically different than a DNS registry. A URN is assigned once and never reassigned, where as a domain name is registered for a specified period and then either renewed or the registration expires and it is returned to the pool of names available for registration.

As I explained in the previous thread, one of the primary motivations for the development of XRI architecture was to bring both reassignable and persistent identifiers together under one unified registration and resolution architecture that could not only solve the usability issues of persistent identifiers (by permitting them to be discovered via human-friendly synonyms), but to enable a new type of registry that supports policies for *both* reassignable and persistent identifiers.

XDI.org is (to my knowledge) the first global identifier registry infrastructure developed using this model. Although the details are probably far too esoteric for most members of this list, if you find yourself interested in the policies of a global registry infrastructure that supports the registration of both reassignable and persistent identifiers, by all means visit the XDI.org Global Services Specifications site and review the main GSS document, in particular the section on I-Numbers.

Net net: as OpenID spreads, so will recognition of the value of having a persistent identifier at the root of an OpenID identity – and so will appreciation of an identifier infrastructure designed from top to bottom to support the policies necessary to make reliance on these persistent identifiers a reasonable risk.

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.