Cryptology ePrint Archive: BibTeX Citation of Report 2013/208

@misc{cryptoeprint:2013:208,
    author = {Yi-Ruei Chen and Cheng-Kang Chu and Wen-Guey Tzeng and Jianying Zhou},
    title = {CloudHKA: A Cryptographic Approach for Hierarchical Access Control in Cloud Computing},
    howpublished = {Cryptology ePrint Archive, Report 2013/208},
    year = {2013},
    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.