SSH key-based authentication is tried-and-true, but it lacks a true
Public Key Infrastructure for key certification, revocation and
expiration.  Monkeysphere is a framework that uses the OpenPGP web of
trust for these PKI functions.  It can be used in both directions: for
users to get validated host keys, and for hosts to authenticate users.

WWW: https://github.com/dkg/monkeysphere