Cryptology ePrint Archive: BibTeX Citation of Report 2011/191

@misc{cryptoeprint:2011:191,
    author = {Johannes Buchmann and Erik Dahmen and Sarah Ereth and Andreas Hülsing and Markus Rückert},
    title = {On the Security of the Winternitz One-Time Signature Scheme},
    howpublished = {Cryptology ePrint Archive, Report 2011/191},
    year = {2011},
    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.