I think I'd rather go with claiming I just got off a contract for a defense contractor, and an NDA prevents me disclosing who it was or what I worked on, other than to say that it involved the same skills that are listed on my resume for my last non-secret employer.
Doesn't have to be a defense contractor. I've signed a contract that basically did not allow me to disclose what or who I was working for to create a software product for a small tv production company. (It fell through)
Same here. I have done work for a number of large companies in software, healthcare, banking, etc. which I can't talk about. It leaves a grey hole in my portfolio.