Cryptology ePrint Archive: BibTeX Citation of Report 2012/645

@misc{cryptoeprint:2012:645,
    author = {Eduarda S. V. Freire,  Kenneth G. Paterson, Bertram Poettering},
    title = {Simple, Efficient and Strongly KI-Secure Hierarchical Key Assignment Schemes},
    howpublished = {Cryptology ePrint Archive, Report 2012/645},
    year = {2012},
    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.