Fully Secure Anonymous HIBE and Secret-Key Anonymous IBE with Short Ciphertexts

Lewko and Waters [Eurocrypt 2010] presented a fully secure HIBE with short ciphertexts. In this paper we show how to modify their construction to achieve anonymity. We prove the security of our scheme under static (and generically secure) assumptions formulated in composite order bilinear groups. In addition, we present a fully secure Anonymous IBE in the secret-key setting. Secret-Key Anonymous IBE was implied by the work of [Shen-Shi-Waters TCC 2009] which can be shown secure in the selective-id model. No previous fully secure construction of secret-key Anonymous IBE is known. ∗Dipartimento di Informatica ed Applicazioni, Università di Salerno, 84084 Fisciano (SA), Italy. †Dipartimento di Informatica ed Applicazioni, Università di Salerno, 84084 Fisciano (SA), Italy.. Work done while visiting the Department of Computer Science of The Johns Hopkins University. ‡Dipartimento di Informatica ed Applicazioni, Università di Salerno, 84084 Fisciano (SA), Italy.