PGP (Pretty Good Privacy)。

RFC 1991 曰く:

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.

PGP was created by Philip Zimmermann and first released, in Version

1.0, in 1991. Subsequent versions have been designed and implemented

by an all-volunteer collaborative effort under the design guidance of

Philip Zimmermann. PGP and Pretty Good Privacy are trademarks of

Philip Zimmermann.