Cryptology ePrint Archive: BibTeX Citation of Report 2015/144

@misc{cryptoeprint:2015:144,
    author = {Tyge Tiessen and Lars R. Knudsen and Stefan Kölbl and Martin M. Lauridsen},
    title = {Security of the AES with a Secret S-box},
    howpublished = {Cryptology ePrint Archive, Report 2015/144},
    year = {2015},
    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.