GNU Privacy Guard (gpg) is a free-software replacement for Symantec’s PGP cryptographic software suite. The software is compliant with RFC 4880, the IETF standards-track specification of OpenPGP. Modern versions of PGP are interoperable with GnuPG and other OpenPGP-compliant systems.
GnuPG encrypts messages using asymmetric key pairs individually generated by GnuPG users. The resulting public keys may be exchanged with other users in a variety of ways. It is also possible to add a cryptographic digital signature to a message, so the message integrity and sender can be verified.
GnuPG also supports symmetric encryption algorithms.