RFC 5408 which describes a Security Architecture for Identity-Based Encryption. It includes protocols for key requests and public parameter requests as well as some basic building blocks for federation. The system described is similar to what Voltage uses for their IBE based encryption solutions. If you are interested in how Identity-Based Encrpytion systems scale in practice and don’t mind reading RFCs, it is a worthwhile read.
Thanks to my co-authors Mark Schertler and Luther Martin. Specifically Luther deserves the majority of the credit for moving this through the process over the past two (or more?) years. Also thanks to Terence Spies at Voltage, as well as Eric Rescorla, Tim Polk and Blake Ramsdell at the IETF for their support.