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Pretty Good Privacy (or PGP) is a computer program which provides cryptographic privacy and authentication. It is a patented technology created by Phil Zimmerman and owned by the PGP Corporation. PGP may encrypt any type of data but it is most commonly used for e‐mail.

OpenPGP is an open‐source (free) alternative standard for digitally signing and encrypting e‐mail. The most common implementation of OpenPGP is GPG, which stands for GNU Privacy Guard.

PGP and GPG are very similar in their uses and operation, but differ in the algorithms that they use. They both use algorithms such as RSA or Elliptic Curve cryptography (ECC) for asymmetric encryption but PGP uses patented symmetric encryption algorithms, while GPG uses public domain (free) algorithms.

Both programs may be used for encrypting/decrypting e‐mail and signing/authenticating messages.

Before using PGP or GPG, a user generates their own public key and private key pair. Then, the public key must be published so that others may access it. This may be done by putting it out on a website, sending out mass emails announcing the public key, or placing it on a key server and associating it to an e‐mail address.