Also I swear to God this has to be like the third repost of NSAKEY in a week.
Just so it's clear: this is from 1999.
The "NSA" in "NSAKEY" could stand for just about anything. Or it could just be some programmer's joke. It's definitely not convincing evidence that this construct has anything to do with the NSA.
Has anyone done a detailed analysis of code referencing the NSAKEY?