Email

OpenPGP is an open standard for encryption and digital signatures of arbitrary data, defined in RFC 4880 (2007) and substantially revised in RFC 9580 (2024, adding Ed25519, X25519, and modern AEAD encryption). GnuPG (GPG) is the dominant open-source implementation, maintained by Werner Koch and the GnuPG project, and the tool most users interact with. OpenPGP predates the PKI/CA model and takes a fundamentally different approach to trust: rather than a hierarchy of certificate authorities that users must trust transitively, OpenPGP uses a Web of Trust in which individual users sign each other’s public keys, and trust is established through chains of personal endorsements. In the Web of Trust model, Alice trusts Bob’s key because she verified it in person and signed it; Carol trusts Bob’s key because Alice (whom Carol trusts) signed it. This decentralised, peer-to-peer trust model made sense for email encryption between individuals who could meet at key-signing parties, but does not scale to automated infrastructure verification, which is why OpenPGP’s role in modern infrastructure is primarily supply chain signing — package repositories, Git commits, and release artifacts — rather than interactive authentication.