Cryptology ePrint Archive: BibTeX Citation of Report 2015/827

@misc{cryptoeprint:2015:827,
    author = {Geumsook Ryu and Kwangsu Lee and Seunghwan Park and Dong Hoon Lee},
    title = {Unbounded Hierarchical Identity-Based Encryption with Efficient Revocation},
    howpublished = {Cryptology ePrint Archive, Report 2015/827},
    year = {2015},
    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.