PGP Protocol Overview

Pretty Good Privacy (PGP) is both a protocol and the name of the program that most widely implements that protocol. The PGP protocol, documented in RFC 1991 and expanded into the OpenPGP proposal (RFC 2440), is a presentation layer protocol that defines a standard to cryptographically secure email messages. RFC 2015 describes how various kinds of PGP messages should be encapsulated using MIME.