One of the "nice" things about the NSA: they rely on pretty standard crypto--the same kind the rest of us do!--for their less sensitive, but still classified, secrets. NSA Ciphersuite B (http://en.m.wikipedia.org/wiki/NSA_Suite_B_Cryptography) is built into a lot of gov/mil communications technology. And it's just RSA, ECDHE, and so on--all that same stuff available in TLS.
In other words: if the NSA break one of these "public" algorithms, you'll be able to tell; they'll soon be picking new Suite B ciphers. (There will be a time-delay, but not of the intentional "let's capture+break foreign transmissions before scaring them away from this cipher" kind. Re-securing our own transmissions takes priority, always. Even if it was broken because of some "quantum leap"--pardon the pun--we have to assume our enemies are advancing their own tech at roughly the same rate, so if we can crack it, they can too.)
In other words: if the NSA break one of these "public" algorithms, you'll be able to tell; they'll soon be picking new Suite B ciphers. (There will be a time-delay, but not of the intentional "let's capture+break foreign transmissions before scaring them away from this cipher" kind. Re-securing our own transmissions takes priority, always. Even if it was broken because of some "quantum leap"--pardon the pun--we have to assume our enemies are advancing their own tech at roughly the same rate, so if we can crack it, they can too.)