PGP FAQ: current answers about OpenPGP and GnuPG
This FAQ answers the questions people ask about PGP today, using the tools people actually run: GnuPG 2.5 on Linux, macOS and BSD, Gpg4win on Windows, and the OpenPGP support built into Thunderbird. Each part is a short list of questions; click a question to open its answer.
What this FAQ covers
"PGP" started in the early 1990s as a single program. Today it means a family of programs that all speak the same open format, called OpenPGP. The format is defined by the IETF; its current version is RFC 9580, published in July 2024. The best-known free program is GnuPG (the GNU Privacy Guard, command name gpg). As of November 2026 its current stable version is 2.5.24, released on September 23, 2026. The older 2.4 branch reached end of life on June 30, 2026, so if your system still has 2.4, plan an upgrade.
The answers here are written for those current versions. Where PGP 2.x or other 1990s software behaved differently, the answer says so in a sentence or two, because old habits (short key IDs, old keyserver names, cleartext-signed mail) still cause trouble.
What changed since the old FAQ
- Algorithms. PGP 2.x used RSA, IDEA and MD5. New GnuPG keys use Ed25519 for signing and Curve25519 for encryption, and RFC 9580 forbids creating new messages with IDEA, Triple-DES or CAST5.
- Keys are named by fingerprint. Short 8-digit key IDs can be faked in seconds, so tools now show the full fingerprint.
- Keyservers. The old pgp.net keyserver network is gone. Keys are now found through keys.openpgp.org, Web Key Directory and similar services. Since GnuPG 2.5.3 there is no built-in default keyserver at all.
- Email. Thunderbird has had OpenPGP built in since version 78 (2020), and Gpg4win adds it to Outlook. PGP/MIME has replaced pasting armored text into the message body.
- Post-quantum work. RFC 9980, "Post-Quantum Cryptography in OpenPGP", was published in June 2026, and GnuPG 2.5 can already create keys with a quantum-resistant encryption subkey.
The parts of this FAQ
Start with the general questions if you are new. If something has gone wrong, go straight to the common problems.
- General questionsWhat PGP, OpenPGP and GnuPG are, how public and private keys work, whether it is legal, what it costs, and which program to use on Linux, macOS and Windows.
- Common problemsFixes for common GnuPG errors: No secret key, No public key, Unusable public key, expired keys, Bad passphrase, pinentry trouble and No keyserver available.
- Security questionsHow secure OpenPGP is today: default algorithms, RSA and ECC key sizes under RFC 9580, quantum computers and RFC 9980, EFAIL, SHA-1 collisions and passphrases.
- KeysAnswers about OpenPGP keys: key IDs versus fingerprints, primary keys and subkeys, Ed25519 or RSA 3072, expiry dates, v4/v5/v6 keys, backups and several addresses.
- Message signaturesHow OpenPGP signatures work: detached, clearsigned and inline signatures, how to verify them, what Good signature, BAD signature and the trust warning mean.
- Key signaturesWhat signing a key means, how to check and certify someone's key with GnuPG, how the web of trust and TOFU work, and why keyservers no longer carry signatures.
- Key revocationHow to revoke an OpenPGP key with GnuPG: the certificate in openpgp-revocs.d, gpg --gen-revoke, publishing it, and what to do after a lost key or passphrase.
- Keyserver questionsWhich OpenPGP keyservers exist in 2026, how to set one in GnuPG, why old keys and missing names show up, removing your data, privacy, and what a keyserver proves.
- Recommended readingThe manuals, standards and books worth reading about PGP and GnuPG in 2026, which old guides are out of date, where to ask questions, and practical tips for daily use.
- How PGP worksA beginner's tour of PGP and GnuPG inside: session keys and hybrid encryption, hashes and signatures, compression, packets, ASCII armor and fingerprints.
- GlossaryPlain definitions of PGP, OpenPGP and GnuPG terms, from AEAD and ASCII armor to subkeys, TOFU, the web of trust, WKD and X25519, following RFC 9580 and the GnuPG manual.
The original 1990s FAQ
The comp.security.pgp FAQ was posted to the Usenet newsgroups of the same name every month in the 1990s and was also published on pgp.net. It describes PGP 2.6.x and PGP 5.x: MIT PGP, the "international" versions, RSA patent issues and DOS command lines. Much of its technical advice is now out of date or unsafe, but it is a good record of how people used PGP at the time. It is kept unchanged in the download archive:
- The comp.security.pgp FAQ (HTML version, all parts)
- The FAQ as a compressed plain-text file (pgpfaq.txt.gz)
The questions in this new FAQ follow the old parts loosely, so you can compare an old answer with the current one. Questions that no longer matter (setting the TZ variable for DOS, MacPGP keyring locations, the "randseed.bin virus" scare) have been dropped.
Where to go next
- To set up GnuPG step by step, use the guides: install GnuPG, then create a key pair.
- To check a file you downloaded, see verifying downloads.
- For terms such as "subkey", "armor" or "web of trust", see the glossary.
Independent site. This FAQ is independent and for information only. It is not written by the GnuPG project or by any company that sells PGP products. For bugs in GnuPG itself, use the GnuPG project's own bug tracker and mailing lists listed on gnupg.org.