Cryptology ePrint Archive: BibTeX Citation of Report 2004/248

@misc{cryptoeprint:2004:248,
    author = {An Braeken and Yuri Borissov and Svetla Nikova and Bart Preneel},
    title = {Classification of Boolean Functions of 6 Variables or Less with Respect to Cryptographic Properties},
    howpublished = {Cryptology ePrint Archive, Report 2004/248},
    year = {2004},
    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.