OpenPGP, PGP und GnuPG

"OpenPGP is the most widely used email encryption standard in the world. It is defined by the OpenPGP Working Group of the Internet Engineering Task Force (IETF) Proposed Standard RFC 2440. The OpenPGP standard was originally derived from PGP (Pretty Good Privacy), first created by Phil Zimmermann in 1991." (Quelle: OpenPGP Alliance)
"PGP (short for Pretty Good Privacy) is a public key encryption program originally written by Phil Zimmermann in 1991. Over the past few years, PGP [...] has become a de-facto standard for encryption of email on the Internet." (Quelle: "Overview of PGP" auf der International PGP Home Page)
"GnuPG [GNU Privacy Guard; GPG] is a complete and free replacement for PGP. Because it does not use the patented IDEA algorithm, it can be used without any restrictions. GnuPG is a RFC2440 (OpenPGP) compliant application. (Quelle: Werner Koch auf der GnuPG-Homepage)
RFC 1991
PGP (Pretty Good Privacy) uses a combination of public-key and conventional encryption to provide security services for electronic mail messages and data files. These services include confidentiality and digital signature. PGP is widely used throughout the global computer community. This document describes the format of "PGP files", i.e., messages that have been encrypted and/or signed with PGP.
RFC 2440
This document provides information on the message-exchange packet formats used by OpenPGP to provide encryption, decryption, signing, and key management functions. It builds on the foundation provided in RFC 1991 "PGP Message Exchange Formats."