Pretty Good Privacy (PGP) is a software program that provides encryption, decryption, digital signature and key management services. PGP was developed by Philip R. Zimmermann starting in 1991. It was later formalized as a specification called OpenPGP as described in RFC4880. PGP is the original implementation of OpenPGP. The GNU Privacy Guard (GPG) is another implementation that avoids encumbered algorithms. In this document, the term PGP is often used instead of OpenPGP to simplify the discussion.