The GNU Privacy Guard (GPG) is a free replacement for the PGP suite of cryptographic software. It is released under the GNU General Public License and was initially developed by Werner Koch and supported by the German government. GPG is completely compliant with the IETF standard for OpenPGP, so the two interact well.
GPG is very stable, production-quality software. It is frequently included in free operating systems, such as the BSDss and GNU/Linux. Although the basic GPG program has a command line interface, there exist various front-ends that provide it with a graphical user interface; for example, it has been integrated into KMail and Evolution, the graphical email clients found in the most popular Linux desktops GNOME and KDE.
GPG features functions to encrypt messages, relying on asymmetric individually generated by GPG users. The public keys that can be exchanged with other users in a variety of ways, for example via Internet keyservers. It is also possible to add a cryptographic digital signature to a message, so the message integrity and sender can be verified.
Since GPG is freely distributable, it does not use the patented IDEA algorithm. Instead, it uses a variety of other, non-patented algorithms such as Triple DES. It is still possible to use IDEA in GPG by downloading a (free) plugin.
GPG can also be compiled for other platforms like Mac OS X and Windows due to its open source nature. For Mac OS X, there is a free port called MacGPG that uses the OS X user interface and native classes.
GPG is a hybrid encryption software program in that it uses a combination of conventional symmetric-key cryptography for speed, and public-key cryptography for ease of secure key exchange.