TrustBearer has become the first public demonstration of an idea this blogger first described in a ThinkWeek paper in 2006: identity management systems create positive externalities. Once built for a purpose, they are often easily extended, adopted or co-opted for completely different objectives. This pattern predates the Web, PKI and even the development of modern computing systems. The classic example is the social security number. Originally introduced by the FDR’s New Deal-era Social Security Administration for the purpose of administering benefits, it has become the de facto identifier for everything from credit rating agencies to some badly designed online banking websites; Fidelity originally used SSN as “username” but later changed the system to allow for choosing nicknames. Drivers licenses were introduced to control who can drive vehicles on public roads. When laws introduced minimum drinking age and imposed penalties for serving to minors, bars found it the natural choice to decide who gets to order drinks. (A bartender in Seattle once declined to server this blogger due to an expired driver’s license.)
Not all of these extensions are necessarily good ideas. In particular the re-purposing of the social security number from a simple identifier into a credential– something that proves identity, never intended in the original design– created the current identity theft mess. In another example, RFID tags are a primitive identity management system designed for tracking inventory; the tag identifies the object it is attached. But when the tags are not deactivated after they are sold to consumers, they can be repurposed for tracking. Each tag emits a constant identifier that can be scanned by anyone with the appropriate transmitter and receiver set up, allowing tracking of individuals in physical space.
Occasionally unofficial extensions to an identity system provides unexpected benefits. Typically there is a very large upfront investment in deploying a system, driven by a well-defined objective. But once the system is built, adding one more person who can use it, or one more website which uses that system for authentication has a small marginal cost. Take for example the Common Access Card or CAC, soon to be replaced by the PIV. These are both PKI systems managed by the Department of Defense, for the purpose of controlling access to systems with national security implications. But once the PKI deployment is operational, individuals have been issued their cards and smart-card readers, they can be used for purposes completely unrelated to defense sector. Case in point: TrustBearer’s OpenID service accepts CAC/PIV cards for authentication to any OpenID enabled relying site. DoD certainly did not design the system for employees to check their personal email accounts or write blog comments in spare time. But given that the smart-cards were already out there in the hands of users, it was a no-brainer for TrustBearer to accept these credentials for strong authentication. Any other website could have done the same: called “SSL client authentication,” the underlying functionality has been supported by web browsers and web servers in some fashion since the late 1990s. The user interface may be clunky because it is rarely seen outside the enterprise context, but all it takes is tweaking some settings in IIS or Apache. The Department of Defense created a positive externality for all websites.
Design matters of course: some technologies are far more amenable to being re-purposed this way. For example, Kerberos is inherently a closed system: adding another relying party requires coordinating with the people in charge. Public-key infrastructure is open by design: once a digital certificate is issued, people can use it to authenticate anywhere. There are still gotchas: revocation checking imposes costs on the identity provider (adding another relying party is not a free lunch when it is hammering the system with revocation checks) or it may not work at all for an entity “outside” the official scope. Some new protocols such as OCSP stapling address that by making freshness proofs portable. More important is the question of acceptable use policy. Just because the cryptography works out does not mean that the official owner of the identity system will approve the creative re-purposing.
That brings us to the European eID deployments. These are national ID systems, with the cards containing PKI credentials. Here is one case where a PKI based system funded by tax-payer money is built with the express intent that anyone can use it for authentication to their service. (This is what governments do after all– they generate externalities, much to the chagrin of libertarians.) Not surprisingly eID cards are also accepted by TrustBearer– specifically Belgian eID. This is an even greater externality because there are bound to be many more of them in existence even today, and this will only improve over time as other EU governments make progress on their deployment. On the other hand, the precedent for using eID online is scarce and chances are most users lack the required card-readers and drivers, while the CAC/PIV users already use their cards regularly in a professional context.