This is a work in progress attempt to build a directory server for Fediverse / ActivityPub in support of encrypted messaging.
This document defines the Fediverse End-to-End Encryption Public Key Directory (FediE2EE-PKD), which consists of ActivityPub-enabled directory server software, a protocol for communicating with the directory server, and integration with a transparent, append-only data structure (e.g., based on Merkle trees).
Some of this overlaps with parts of what the PLC directly / DID docs do, except it also proposes a federated model.