Long live minimal disclosure tokens!

Stefan Brands has a nice new piece called, Anonymous Credentials? No, Minimal Disclosure Certificates!  I think he's right about the need to stay away from the moniker “anonymous credentials”.  I adopted it – in spite of the confusion it creates – but I hereby give it up.  If I use it again, slap me around:

“Kim Cameron is in the midst of blogging an excellent series of posts on the important topic of unlinkability; see here and here, for instance. As I had expected from past experience, several commentors on Kim’s post (such as here and here) wrongly equate unlinkability with anonymity. Of course, an unfortunate choice of terminology (‘anonymous credentials’) does not help at all in this respect… 

“In short, ‘anonymous credentials’ are not all about anonymity. They are about the ability to disclose the absolute minimum that is required when presented an identity claim. Similarly, ‘unlinkability’, ‘untraceability’, and ‘selective disclosure’ are not about anonymity per se.

“Anonymity is just an extreme point on the privacy ‘spectrum’ that can be achieved, all depending on what attribute information is encoded in certificates and what of that is disclosed at presentation time. Currently prevalent technologies, such as standard digital signatures and PKI/X.509 certificates, are a poor technology to protect identity claims, since they inescapably leak a lot of identifying information when presenting protected identity claims; in particular, they disclose universally unique identifiers (correlation handles) that can be used to unambiguously link their presentation to their issuance.

I hope people will think hard about the difference between privacy and anonymity to which Stefan calls our attention.  Both are important, but people in the privacy community consider it crucial not to conflate them.  I'll try to find pointers to some of the detailed analysis that has been done by people like Simon Davies of Privacy International and Ann Cavoukian, Privacy Commisioner of Ontario, in this area – not to mention a host of other advocates and policy specialists.

So I'm going to STOP saying anonymous credentials, and even fix my very time-consuming graphic!  (Is that true dedication or what??) 

But I hope Stefan will allow me to say “Minimal Disclosure Tokens” rather than “Minimal Disclosure Certificates”.  I know the word “token” can possibly be confused with a hardware second factor, but its usage has become widely accepted in the world of web services and distributed computing.  Further, I want to get away from the connotations of X.509 “certificates” and forge new ground.  Finally, the word “tokens” ties in to thinking about claims, and allows us to envisage not only “hiding” as a means of minimization, but less draconian mechanisms as well.