Construction of a hybrid HIBE protocol secure against adaptive attacks (without random Oracle)

Abstract

We describe a hybrid hierarchical identity based encryption (HIBE) protocol which is secure in the full model without using the random oracle heuristic and whose security is based on the computational hardness of the decisional bilinear Diffie-Hellman (DBDH) problem. The new protocol is obtained by augmenting a previous construction of a HIBE protocol which is secure against chosen plaintext attacks (CPA-secure). The technique for answering decryption queries in the proof is based on earlier work by Boyen-Mei-Waters. Ciphertext validity testing is done indirectly through a symmetric authentication algorithm in a manner similar to the Kurosawa-Desmedt public key encryption protocol. Additionally, we perform symmetric encryption and authentication by a single authenticated encryption algorithm. A net result of all these is that our construction improves upon previously known constructions in the same setting. © Springer-Verlag Berlin Heidelberg 2007.