As the standard RPC call are being used more and more to convey information that may need to be auditable, some messages could need to carry additional security. Namely, some message could need to be signed and contain an incremental number incremented on each host.
If done correctly, this could allow to trace a series of messages (for example, billable events) and ensure that it has not been tempered with and that messages are not missing.
See also session http://summit.openstack.org/cfp/details/118 which is a precursor to that.
Based on a discussion we started with Eric Windisch, this effort is common with the work he stated and we will be joining our efforts in this session and hopefully in the future work.
https://blueprints.launchpad.net/nova/+spec/trusted-messaging