From Wikipedia (http://en.wikipedia.org/wiki/Enigma_machine): "Although Enigma had some cryptographic weaknesses, in practice it was only in combination with procedural flaws, operator mistakes, captured key tables and hardware, that Allied cryptanalysts were able to be so successful."The Enigma cipher is just a complex substitution cipher. Those are pretty weak. PGP is based on public key cryptography, which requires factoring enormous integers in order to recover the private key. It's a lot harder to break than a substitution cipher.