Cryptology ePrint Archive: BibTeX Citation of Report 2004/040

@misc{cryptoeprint:2004:040,
    author = {Lizhen Yang, Kefei Chen},
    title = {Cryptanalysis of a timestamp-based password authentication scheme},
    howpublished = {Cryptology ePrint Archive, Report 2004/040},
    year = {2004},
    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.