1) GPL/LGPL are not incompatible with iOS, they are incompatible with the App Store. I don't care about that. I was writing a GPL'd app, and I would be pleased with a GPL'd library. iOS was also not my only target. (response to one of your other posts)
2) The idea of 'what's enough' was for e-mail decryption only. Which is what I wanted to do. And I wrote an open-source OpenPGP library to do it: https://github.com/mrmekon/libsimplepgp
3) I don't need 'some library to solve encryption and decryption', I need 'some library to solve decryption of PGP-encrypted emails.' A partial implementation of OpenPGP, as a library. Other crypto packages don't support the OpenPGP packet format.
4) Read section 4, "Packet Syntax", the entire concept behind the OpenPGP format: http://www.ietf.org/rfc/rfc2440.txt