How can you tell an extrovert from an introvert at NSA? Va gur ryringbef, gur rkgebireg ybbxf ng gur BGURE thl'f fubrf.
I found this joke on USENET, but the punchline is scrambled. Maybe you can decipher it? According to Wikipedia, ROT13 (http://en.wikipedia.org/wiki/ROT13) is frequently used to obfuscate jokes on USENET.
Hint: For this task you're only supposed to substitue characters. Not spaces, punctuation, numbers etc.
Test examples:
"EBG13 rknzcyr." -->
"ROT13 example."
"This is my first ROT13 excercise!" -->
"Guvf vf zl svefg EBG13 rkprepvfr!"