I’m not going to re-iterate what selective disclosure is good for and apparently my friend Ben Hyde has spared me from the need to be cynical, though I think (I am not a lawyer!) he is wrong: the OSP applies to each individual specification – you are not required to use them in the context of each other.
So, for now, I will just celebrate the fact that Microsoft has finally made good on its promise to open up the technology, including BSD-licensed code. Though I guess I will have to inject one note of cynicism: a quick glance at the specification (you can get it here) suggests that they have only opened up the most basic use of the technology: the ability to assert a subset of the signed claims. There’s a lot more there. I hope they plan to open that up, too (how long will we have to wait, though?).