Hierarchical Identity Based Encryption with Constant Size Ciphertext

Authors: D. Boneh, E. Goh, and X. Boyen

We present a Hierarchical Identity Based Encryption (HIBE) system where the ciphertext consists of just three group elements and decryption requires only two bilinear map computations, independent of the hierarchy depth. Encryption is as efficient as in other HIBE systems. We prove that the scheme is selective-ID secure in the standard model and fully secure in the random oracle model. Our system has a number of applications: it gives a very efficient forward secure encryption system (where ciphertexts are short), it converts the NNL broadcast encryption system into an efficient public key broadcast system, and it provides an efficient mechanism for encrypting to the future. The system also supports limited delegation where users can be given restricted private keys that only allow delegation to certain descendants. Sublinear size private keys can also be achieved at the expense of some ciphertext expansion.

In proceedings of Eurocrypt '05, LNCS 3493, pp. 440-456

Full paper: pdf