PGP web of trust

The OpenPGP web of trust is the trust model in which the authenticity of a public key is established by signatures from other key-holders whose own keys are trusted by the verifier — building a directed graph in which trust propagates by transitive signature rather than by a centralised certificate authority. Where TLS establishes the authenticity of a domain’s key by a chain of trust rooted in a small set of pre-installed certificate authorities, PGP establishes the authenticity of a key by signatures from individuals who themselves have either been authenticated by the verifier (a “direct trust” relationship) or, transitively, by individuals the verifier directly trusts.

The mechanic permits an operator-side authentication pattern that does not require any third-party institution. A journalist who has met a source in person, exchanged key fingerprints, and signed each other’s keys creates a direct trust relationship. A third party who knows neither but who has signed the journalist’s key can — under appropriate policies — extend their trust through the journalist to the source. The aggregate effect is a federated authentication graph that operates independently of state-issued credentials or commercial certificate authorities.

In practice the web-of-trust scales poorly to the global internet. Most users do not maintain key-signing discipline; most signatures in the public keyservers are weakly authenticated; the keyserver infrastructure has been subject to malicious-signature flooding attacks that destabilised the WoT in 2019. The model remains operationally useful at small scale — within a newsroom, within a research collective, within a specific investigative project — where the participants can practise sufficient key-signing discipline to make transitive trust meaningful.

For an offshore-hosting operator the PGP web of trust is the authentication mechanism on which the publication’s warrant canary signature is grounded, on which secure subscriber communications outside the contact-form channel can be conducted, and on which the per-editor authentication chain is anchored. The publication has set out the editor key fingerprints on the /principles/team page; subscribers who wish to verify the operator’s outbound communications can build a trust path from any commonly-rooted public key.