I think it depends. A careful reading of the classification guides might let a candidate discuss a lot of technical details.
OTOH, I'd hate to be in a position where I had to think carefully about every aspect of that stuff during an interview. Even if nobody noticed an inadvertent classified spill, it could still suck.
No. You may not even talk around the topics. This explicitly comes with the training. Anyone asks me about my last job, I don’t really state much more than what the job title was and what the job postings said for the role I applied to.
I work with people who have worked on various classified projects in years past. Once in a while someone will mention something about the project they read in a newspaper and they have to say "It is obviously unclassified now but because I wasn't explicitly told that is was no longer classified I am not allowed to talk about it" - then they change the subject.
OTOH, I'd hate to be in a position where I had to think carefully about every aspect of that stuff during an interview. Even if nobody noticed an inadvertent classified spill, it could still suck.