Cryptology ePrint Archive: BibTeX Citation of Report 2015/661

@misc{cryptoeprint:2015:661,
    author = {Shane Kepley and David Russo and Rainer Steinwandt},
    title = {Cryptanalysis of a modern rotor machine in a multicast setting},
    howpublished = {Cryptology ePrint Archive, Report 2015/661},
    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.