Identity-based Hierarchical Designated Decryption *

This paper presents an identity-based hierarchical designated decryption (IHDD) scheme which allows a message sender to generate ciphertexts that can be decrypted by (1) only a specified recipient or (2) a specified recipient and all or some of its ancestor users in the hierarchy tree. The newly proposed scheme can be considered as a combination of the hierarchical identity-based encryption (HIBE) and the identity-based multirecipient encryption scheme (ID-based MRES). However, the purpose and structure of the proposed IHDD scheme are different from those of the HIBE and the ID-based MRES. The proposed IHDD scheme has low computation complexity, in which the decryption operation needs only one bilinear pairing computation, and constant length private keys wherein the length of users ’ private keys is independent of the hierarchy depth. The security of the proposed scheme is based on the decision bilinear Diffie-Hellman inversion assumption without using random oracles