G. Vanrenen, S. Smith, J. Marchesini, "Distributing security-mediated PKI," International Journal of Information Security 5(1), 3-17, January 2006.

Abstract  Abstract The security-mediated approach to PKI offers several
advantages, such as instant revocation and compatibility with standard RSA
tools. In this paper, we present a design and prototype that addresses its trust
and scalability problems. We use trusted computing platforms linked with
peer-to-peer networks to create a network of trustworthy mediators and improve
availability. We use threshold cryptography to build a back-up and migration
technique which allows recovery from a mediator crashing while also avoiding
having all mediators share all secrets. We then use strong forward secrecy with
this migration, to mitigate the damage should a crashed mediator actually be
compromised.

http://dx.doi.org/10.1007/s10207-005-0076-x