Nowadays [i.e. circa 2000], I've stopped using PGP - ever since I wrote my own compatible crypto application from scratch. Frankly the coding style used in all the versions of PGP I've seen (2.6ui, 2.6.2i, and the version 5 stuff laboriously scanned in during summer '97) has been pretty low quality.
Cryptography and privacy are important - so I'd rather use something coded cleaner and more tightly. And being smaller and tighter, it's easier for you out there to read and review.
So head to the project pagefor the details of CTClib.