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# Notes on OpenPGP
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An introduction to the concepts of OpenPGP, aimed mainly at software
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developers who are looking to use OpenPGP functionality in their projects.
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2023-09-15 11:14:06 +02:00
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This document describes
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[OpenPGP version 6](https://datatracker.ietf.org/doc/draft-ietf-openpgp-crypto-refresh/),
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with occasional remarks about differences to earlier versions.
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This text is *not* intended as a guide for end-users who use OpenPGP-related software.
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## What is OpenPGP?
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OpenPGP is an open standard for cryptographic operations.
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It has grown out of the
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["Pretty Good Privacy (PGP)"](https://en.wikipedia.org/wiki/Pretty_Good_Privacy)
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software.
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OpenPGP is an open standard, there are many widely used
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(and [interoperable](https://tests.sequoia-pgp.org/)) implementations.
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## A very brief history
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The OpenPGP standard has evolved over time.
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(Also see https://www.openpgp.org/about/history/)
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### "Pretty Good Privacy (PGP)"
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The earliest roots of OpenPGP trace back to *"Pretty Good Privacy (PGP)"*,
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a software program, written by Phil Zimmermann and first released in 1991.
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The original PGP software has played a role in the political struggles sometimes
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referred to as the ["Crypto Wars"](https://en.wikipedia.org/wiki/Crypto_Wars)
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(also see https://en.wikipedia.org/wiki/Crypto_(book) for some of that history,
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including about the history of PGP).
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The "PGP" software was never under a Free Software license,
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even though its source code has at one point been widely published.
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The ownership and branding of the product has
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[changed over the years](https://en.wikipedia.org/wiki/Pretty_Good_Privacy#PGP_Corporation_and_Symantec),
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The software enjoys a continued existence, albeit with
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[changing name and scope](https://en.wikipedia.org/wiki/Pretty_Good_Privacy#PGP_Corporation_encryption_applications).
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### Standardizing OpenPGP
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While the PGP software was developed as a commercial product, the owner at the time,
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"PGP Inc." started a standardization effort with the IETF in July 1997.
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The resulting open standard was named
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[OpenPGP](https://en.wikipedia.org/wiki/Pretty_Good_Privacy#OpenPGP).
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The result of this early standardization work is
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[RFC 2440 "OpenPGP Message Format"](https://datatracker.ietf.org/doc/html/rfc2440),
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published November 1998.
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The name "OpenPGP" can be used freely by implementations (unlike the name
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"PGP", which is a [registered trademark](https://uspto.report/TM/74685229)).
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### GnuPG, a free software implementation
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[First released 1997-12-20](https://gnupg.org/download/release_notes.html#sec-2-70),
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GnuPG is an implementation of the OpenPGP standard.
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GnuPG has been the major Free Software implementation of OpenPGP for a period
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of time. It has played an important and successful role in the release of NSA
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documents by [Edward Snowden](https://theintercept.com/2014/10/28/smuggling-snowden-secrets/).
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## The present
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### Multiple major implementations
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Today, multiple implementations of OpenPGP play an important role:
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- Protonmail, who provide email encryption services for a large number of users,
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use (and maintain) [OpenPGP.js](https://openpgpjs.org/).
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- The Thunderbird email software is using the [RNP](https://www.rnpgp.org/)
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implementation for their built-in OpenPGP support since version 78 (released in mid-2020).
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- The RPM Package Manager software includes an OpenPGP backend based on
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[Sequoia PGP](https://sequoia-pgp.org/), a modern OpenPGP implementation in Rust.
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Fedora [uses Sequoia PGP in rpm](https://sequoia-pgp.org/blog/2023/04/27/rpm-sequoia/)
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since version 38.
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### OpenPGP version 6
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This document mainly describes OpenPGP version 6, which brings many updates of the core cryptographic mechanisms,
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compared to the previous version 4.
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As of this writing (in 2023), version 4 of OpenPGP is still most commonly used.
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OpenPGP version 4 is described in [RFC 4880](https://datatracker.ietf.org/doc/html/rfc4880).
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