GnuPG - The GNU Privacy Guard suite of programs
GnuPG is a set of programs for public key encryption and digital
signatures. The program most users will want to use is the OpenPGP
command line tool, named gpg. gpgv is a stripped down version of gpg
with no encryption functionality, used only to verify signatures
against a trusted keyring. There is also a tool called gpgsplit to
split OpenPGP messages or keyrings into their component packets. This
is mainly useful for seeing how OpenPGP messages are put together.