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.