Cryptology ePrint Archive: BibTeX Citation of Report 2013/578

@misc{cryptoeprint:2013:578,
    author = {Oleksandr Kazymyrov and Valentyna Kazymyrova and Roman Oliynykov},
    title = {A Method For Generation Of High-Nonlinear S-Boxes Based On Gradient Descent},
    howpublished = {Cryptology ePrint Archive, Report 2013/578},
    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.