Unbounded Hierarchical Identity-based Encryption in the Standard Model

In this work, a new construction of hierarchical identity-based encryption(HIBE) is proposed. The new construction is unbounded in the sense that the public keys can not impose the additional limitations on the functionality of the systems. In the well known construction, the size of private keys and ciphertexts depends on the depth of the identity. Our construction avoids this limitation. The new scheme achieves the constant size private keys and ciphertexts, which solves the trade-off between the private keys size and the ciphertexts size. In the standard model, the new scheme is provably secure where the security is reduced to n+1-BDHE problem.