Adaptively Secure Revocable Hierarchical IBE from k-linear Assumption
Revocable identity-based encryption (RIBE) is an extension of IBE with an efficient key revocation mechanism. Revocable hierarchical IBE (RHIBE) is its further extension with key delegation functionality. Although there are various adaptively secure pairing-based RIBE schemes, all known hierarchical analogues only satisfy selective security. In addition, the currently known most efficient adaptively secure RIBE and selectively secure RHIBE schemes rely on non-standard assumptions, which are referred to as the augmented DDH assumption and qtype assumptions, respectively. In this paper, we propose a simple but effective design methodology for RHIBE schemes. We provide a generic design framework for RHIBE based on an HIBE scheme with a few properties. Fortunately, several state-of-the-art pairing-based HIBE schemes have the properties. In addition, our construction preserves the sizes of master public keys, ciphertexts, and decryption keys, as well as the complexity assumptions of the underlying HIBE scheme. Thus, we obtain the first RHIBE schemes with adaptive security under the standard k-linear assumption. We prove adaptive security by developing a new proof technique for RHIBE. Due to the compactness-preserving construction, the proposed R(H)IBE schemes have similar efficiencies to the most efficient existing schemes. ∗This work is supported by JST CREST Grant Number JPMJCR14D6, JSPS KAKENHI Grant Number JP17K12697, JP18H05289, and MEXT Leading Initiative for Excellent Young Researchers. †National Institute of Information and Communications Technology (NICT), Japan. {k-emura, takayasu}@nict.go.jp ‡The University of Electro-Communications, Japan. watanabe@uec.ac.jp §National Institute of Advanced Industrial Science and Technology (AIST), Japan.