OpenPGP is the most widely used email encryption standard. It is defined by the OpenPGP Working Group of the Internet Engineering Task Force (IETF) as a Proposed Standard in RFC 4880. OpenPGP was originally derived from the PGP software, created by Phil Zimmermann.
Although OpenPGP’s main purpose is end-to-end encrypted email communication, it is also utilized for encrypted messaging and other use cases such as password managers.
For all operating systems
OpenPGP is available for all major platforms, such as Windows, Mac OS, GNU/Linux, Android, and iOS.
Standing the test of time
OpenPGP was standardized in 1997 and since then continuously improved. As far as we know, intelligence organizations aren’t able to break it.