# Hierarchical Identity Based Encryption with Constant Size Ciphertext

**Authors:**

*D. Boneh, E. Goh, and X. Boyen*

** Abstract: **

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.

** Reference:**

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

**Full paper:**
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