[PGP Web of Trust: Core Concepts Behind Trusted Communication](https://www.linux.com/training-tutorials/pgp-web-trust-core-concepts-behind-trusted-communication/),
[PGP Web of Trust: Delegated Trust and Keyservers](https://www.linuxfoundation.org/blog/pgp-web-of-trust-delegated-trust-and-keyservers/) [Konstantin Ryabitsev, 2014]