PNA is not one of the major encryption types used these days. Bitcoin uses elliptic curve cryptography, specifically the Diffie-Hellman variety, and despite the fact that the NSA had an hand in the development of elliptic curve crypto, virtually all bitcoiners who are trained in encryption agree that Satoshi chose the very most transparent (as in no backdoors) encryption available to date.Something about the "Prime Number Algorithm", and getting it down to a 24% probability, essentially meaning virtually all encryption we use has been back doored by the NSA / CIA?
The crypto used on your bank's website, for instance, is a different variety of elliptic curve cryptography, and it uses keypairs too although we never think of it as doing so... The browser basically holds our private key for us as we log into secure websites.
The NSA likely has that lessor-transparent variety backdoored, but it's not proven yet.