OpenPGP
OpenPGP is an open standard that describes a message (file) format originally used by the Pretty Good Privacy (PGP) program, initially developed by Phil Zimmermann in 1991. A number of standard-track Request for Comment documents augment its functionality, one example being PGP/MIME which defines the use of OpenPGP in email via MIME. OpenPGP's encryption can ensure the secure delivery of files and messages, as well as provide verification of who created or sent the message using a process called digital signing.