Private Anonymous Messaging

Messaging systems where a user maintains a set of contacts and broadcasts messages to them is very common. We address the problem of a contact obtaining a message that it missed, from other contacts of the user while maintaining anonymity of all parties involved. We identify a set of requirements in addressing this problem and propose a modification to the hierarchical identity based encryption scheme proposed by Boneh et. al. We briefly present an implementation of the proposed cryptographic primitives as a proof of concept.