I know that's not what the principal posits, but that's an attitude I frequently encounter, and I find it profoundly annoying, for some reason.
Banks have window facades for a reason... Transparency is also a way of increasing security. It cuts both ways.
Consider a weakness in a hash algorithm. If found by a 3rd party, you want this information to be publicly announced as soon as possible (be you Alice or Chuck), but that's only possible if the algorithm is widely available in the first place.
Bruce Schneier ties it in with a belief that all security systems must be designed to fail as gracefully as possible:
Is it REALLY necessary to add that to the entry?
Unless of course you mean common knowledge among computer scientists and cryptographers, in which case "common" is rather rare.
1. not everyone is familiar with cryptology, actually the majority of people aren't.
2. IMO it is extremely relevant to the NSA. If there was complete transparency but an elegant system, we can have a secure country.