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GnuPG

A free implementation of the OpenPGP standard.

GnuPG (gpg) is a free implementation of the OpenPGP standard for signing, verifying, encrypting, and decrypting data. It implements public-key cryptography for messages and files, manages a keyring of identities, supports a Web of Trust model for verifying who owns which key, and integrates with mail clients through the OpenPGP message format.

GnuPG is the basis for signed Linux package repositories (every Debian, Fedora, Arch repository signs its package metadata with a GPG key that the package manager verifies), encrypted email (Thunderbird's built-in OpenPGP support, the older Enigmail, KMail's signing), and the secure distribution of source releases for many open-source projects.

Werner Koch started GnuPG in 1997 and has continued as the lead maintainer. The project is GPL-3.0 and is funded primarily by contracts with infrastructure and security organisations plus public donations. GnuPG has gone through several modernisation efforts (the move from the old SKS keyserver network to keys.openpgp.org / WKD, the integration of ECC keys, the gpg-agent split) that have kept the implementation current despite its age.

Debian/Ubuntu: sudo apt install gnupg
Fedora/RHEL:   sudo dnf install gnupg2
Arch:          sudo pacman -S gnupg
macOS:         brew install gnupg