Cryptology ePrint Archive: BibTeX Citation of Report 2006/225

@misc{cryptoeprint:2006:225,
    author = {Giuseppe Ateniese and Alfredo De Santis and Anna Lisa Ferrara and Barbara Masucci},
    title = {Provably-Secure Time-Bound Hierarchical Key Assignment Schemes},
    howpublished = {Cryptology ePrint Archive, Report 2006/225},
    year = {2006},
    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.