Gnu Privacy Guard
GnuPrivacyGuard (GPG) brings GnuPG, the most trusted name in encryption, to Android. Easily encrypt, decrypt, sign and verify files of any kind, just by sharing them to GPG. This app aims to provide a complete, integrated crypto toolkit integrated into the Android experience. GPG provides solid encryption for files private, and for verifying that files are who you think they are. It includes optimizations to make it operate many times faster than other encryption packages.
GPG provides an integrated experience, so clicking on OpenPGP files "just works". You can also share files to GPG to decrypt, encrypt, sign, or verify them. GPG will respond when you click on a OpenPGP fingerprint URL (one that starts with openpgp4fpr:). GPG also gives you complete command line access to the entire GnuPG suite of encryption software.