No, it's the other way around: SDSI was deprecated for SPKI, which took a lot of its ideas about naming from SDSI.
> both of which AFAIK haven't been touched in ~20 years (which is fine by me, if the theory and implementation are solid, but SDSI has CORBA/J2EE smells all over the RFC from what I remember. Lightweight, eh...)
SPKI is indeed old, but the fundamental ideas are really good, and some of them (the cert calculus) are timeless. It needs a v2.0 to update the recommended crypto, specify some more use cases and so forth. But it's really, _really_ good, far better than XPKI and extremely capable.
And still pretty lightweight.
All of the resources I've searched for are fairly old, do you have anything more recent that I can read up on? I see a 2006 paper, but not much other than that.
[1] Though I'm well aware that having an open-standard available for a long time doesn't mean squat, as evidenced by Heartbleed-esque bugs.
Edit: Reading the '00 "A Formal Semantics for SPKI" Howell, Katz, Dartmouth. This is what I was looking for.
In particular, I liked the tuple-calculus they define; it can be extended to support just about any permission I can think of (although it does require reversing DNS names, which is slightly ugly).
I have a scheme to release a v2.0 of the standard someday in my copious free time.
RFCs 2692 & 2693 specify a really great, lightweight, way to do that. They resulting certificates needn't be a whole lot heavier than a JWT, and are much lighter-weight than and X.509 certificate. The RFCs also specify an intelligent, domain-neutral algorithm for performing calculations on tags (what JWT refers to as 'claims') and keys.
It's a pretty awesome solution, and there are a lot of good ideas in there. A streamlined version could, I think, end up being competitive with JWTs.