Anonymous identity based encryption with traceable identities

We introduce Anonymous Identity Based Encryption with Traceable Identities, in which we provide a new feature to anonymous identity-based encryption schemes: lifting the anonymity of some specific recipients in necessary situations (such as when they are suspected as criminals). Our primitive allows a tracer, given a tracing key associated to an identity, to filter all the ciphertexts that are sent to this specific identity (and only those). As it is primordial to preserve the privacy of the law-abiding users, the security takes into account the collusion of tracers and corrupted users. We first start with the Boyen Waters IBE and then proceed further to the class of IBKEM based on Hash Proof Systems proposed by Blazy et.al [4]. By reinforcing the notion of affine MAC, we show that these IBE schemes can be transformed to AIBET. Interestingly, our transformation does not weaken the original schemes: even though the adversary is allowed to get access to some additional oracles as we add a new functionality, the security relies on the same underlying security assumptions and the efficiency is almost unchanged, only some extra keys are added but the encapsulation / decapsulation process remain the same.