Cryptology ePrint Archive: BibTeX Citation of Report 2013/022

@misc{cryptoeprint:2013:022,
    author = {James McLaughlin and John A. Clark},
    title = {Nonlinear cryptanalysis of reduced-round Serpent and metaheuristic search for S-box approximations.},
    howpublished = {Cryptology ePrint Archive, Report 2013/022},
    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.