Note: The developer marked this project as "fallen asleep" on 2017-09-10,
so you should rather use it's succesor https://f-droid.org/packages/org.sufficientlysecure.keychain. It
has evolved very much, a much more active and well managed development
community.
APG is a port of OpenPGP for Android. Use it to encrypt and decrypt files, and
in conjunction with K-9 Mail, to seamlessly add support for encrypting and
decrypting emails, as well as adding and verifying digital signatures.