Cryptology ePrint Archive: BibTeX Citation of Report 2010/188

@misc{cryptoeprint:2010:188,
    author = {Yan Zhu and Gail-Joon Ahn and Hongxin Hu and Huaixi Wang},
    title = {Cryptographic Role-based Security Mechanisms based on Role-Key Hierarchy},
    howpublished = {Cryptology ePrint Archive, Report 2010/188},
    year = {2010},
    note = {\url{http://eprint.iacr.org/}},
}

You will need the url.sty package (comes with most LaTeX installations) for the last line. Otherwise, remove the \url command.