An identity-based key infrastructure suitable for messaging and its application to e-mail

Identity-based encryption (IBE) systems are relatively recently proposed; yet they are highly popular for messaging applications since they offer new features such as certificateless infrastructure and anonymous communication. However, recent studies also reveal that the infrastructure needed for IBE systems may be as complicated as the conventional public key cryptosytems and not sufficient research has been conducted in relevant issues concerning the infrastructure. In this paper, we intended to propose an IBE infrastructure for messaging applications. The proposed infrastructure requires one registration authority and at least one public key generator and they secret share the master secret key. In addition, the PKG also shares the same master secret with each user in the system in a different way. Therefore, the PKG will never be able to learn the private keys of users under non-collusion assumption. Users can also select meaningful pseudonyms and communicate anonymously using them with other users in the system. We discuss different aspects of the proposed infrastructure such as security, key revocation, uniqueness of the identities, and non-repudiation that constitute the main drawbacks of other IBE schemes. We demonstrate that our infrastructure solves many of these drawbacks under certain assumptions. We also provide some implementation results to show the feasibility of the proposed infrastructure.