@misc{cryptoeprint:2009:293,
    author = {Jin Li and Qian Wang and Cong Wang and Kui Ren},
    title = {Enhancing Attribute-based Encryption with Attribute Hierarchy},
    howpublished = {Cryptology ePrint Archive, Report 2009/293},
    year = {2009},
    url = {http://eprint.iacr.org/2009/293},
}