General PGP questions: what OpenPGP and GnuPG are, cost, platforms

PGP ("Pretty Good Privacy") was a program written by Phil Zimmermann in the early 1990s. It let ordinary people encrypt messages with public-key cryptography and sign them digitally. Its file and message format was later turned into an open standard, so that many programs could read each other's messages.

The name "PGP" is now used loosely for that whole family: the standard, the programs that implement it, and the keys and messages they produce. If someone asks for "your PGP key", any OpenPGP program will do. For the full story, see the history of PGP.

• PGP is the original program and the brand name used by its commercial successors.
• OpenPGP is the open standard for the message format, published by the IETF. The PGP 2.x format was described in RFC 1991 (1996); OpenPGP itself was published as RFC 2440 (1998), then RFC 4880 (2007), and now RFC 9580 (July 2024). RFC 9980 (June 2026) adds post-quantum algorithms.
• GnuPG (GNU Privacy Guard, command gpg) is a free implementation of OpenPGP, first released in 1997. It is the program most Linux distributions ship and the engine behind Gpg4win on Windows.

There is one complication. The GnuPG developers did not adopt all of RFC 9580 and instead follow a separate specification called LibrePGP, published as an individual Internet-Draft (not an IETF working-group document). Everyday version 4 keys and messages work across both camps. The details are in OpenPGP standards.

Every user makes a key pair. The public key is meant to be shared: you publish it, send it to friends, put it on a keyserver. The private key (also called the secret key) stays on your own computer or smartcard, protected by a passphrase.

People use your public key to encrypt messages to you; only your private key can decrypt them. You use your private key to sign; anyone with your public key can check the signature. So you never need to share a secret in advance, which was the big step forward of public-key cryptography.

In practice OpenPGP is a hybrid system: the message itself is encrypted with a fast, random one-time session key (for example with AES), and only that session key is encrypted with the public key. How PGP works explains this step by step.

Email normally crosses several servers and is stored in mailboxes you do not control. Encryption keeps business documents, medical letters, passwords and private conversations readable only by the people they are meant for. Signatures solve a different problem: they prove a message or a software download really came from the person it claims to come from and was not changed on the way. You can use one without the other.

GnuPG is free software under the GNU General Public License: you may use it, copy it and change it at no cost, at home or at work. Gpg4win, the Windows distribution, is also free software. Thunderbird's built-in OpenPGP support is part of the free mail client.

In the 1990s this was a real question, and the old FAQ spent a lot of space on patents and licences for PGP 2.x. None of that matters for GnuPG: its licence lets everyone use it free of charge, for any purpose.

In most countries it is legal to use encryption for your own files and messages. A few countries restrict its use or require licences, and some have laws that can oblige you to hand over keys or passwords during an investigation. Export of encryption software and products is also regulated in many places. The rules differ by country and change over time, so check the current law where you live, and ask a lawyer if you have a specific case. This FAQ cannot give legal advice.

The legal battles PGP went through in the 1990s are covered on the history page.

• Linux and BSD: GnuPG. Common Linux distributions already include it in the base system, although the packaged version may be older than the newest release.
• Windows: Gpg4win, the official GnuPG distribution for Windows. It includes GnuPG, the Kleopatra key manager, GpgOL for Microsoft Outlook and GpgEX for Windows Explorer. As of November 2026 the current release is 5.1.1 (September 23, 2026); since version 5.0.0 it supports only 64-bit Windows 10 (1809 or later) and Windows 11.
• macOS: GnuPG's download page points to the installer from the GPGTools project and to a separate "GnuPG for OS X" installer.
• Email: Thunderbird has OpenPGP built in since version 78. It uses its own engine (the RNP library), not GnuPG, so it needs no extra software.

For step-by-step setup, see installing GnuPG and encrypted email.

As of November 2026, GnuPG 2.5.24 (released September 23, 2026) is the current stable version. The 2.5 series was declared stable in December 2025 and leads to a future 2.6. The previous 2.4 branch reached end of life on June 30, 2026, and 2.2 on December 31, 2024. GnuPG 1.4 is a legacy single-program version that receives only important security updates; its one remaining use is reading old PGP 2 keys. Always check the download page on gnupg.org for the latest release.

Yes. Some examples:

• RNP, the library Thunderbird uses for its OpenPGP support.
• Sequoia PGP, an OpenPGP implementation written in Rust, with a command-line tool called sq.

Messages and version 4 keys made with any of these normally work with the others, because they share the OpenPGP format.

Yes. GnuPG's standard library for this is GPGME ("GnuPG Made Easy"). It runs GnuPG for you and gives a stable programming interface, with C++ and Qt bindings (GpgME C++ and QGpgME) published by the GnuPG project. Calling gpg directly from scripts also works: use --batch, read the machine-readable --status-fd output rather than the human messages, and check the exit code. For checking signatures in scripts, GnuPG recommends gpgv or the --assert-signer option (see message signatures).

According to the GnuPG project, GnuPG runs on GNU/Linux on many processor types (amd64 is the main development platform; arm64, armhf, PowerPC and others are tested from time to time), on 64-bit Windows 10 and 11, on macOS, and on OpenBSD, FreeBSD, NetBSD, AIX and Solaris. Old ports of GnuPG 1.4 exist for systems such as OpenVMS and RISC OS. The old FAQ listed PGP 2.x for DOS, Amiga, Atari and others; those versions are kept in the download archive for history only.

Not GnuPG 2.x. PGP 2 used version 3 RSA keys with the IDEA cipher and MD5, which modern GnuPG no longer accepts. If you must open an archive of old PGP 2 messages, GnuPG's download page notes that the legacy GnuPG 1.4 branch still supports these unsafe PGP-2 keys. Decrypt the old data once, then re-encrypt anything you want to keep with a new key.