Cryptology ePrint Archive: BibTeX Citation of Report 2004/050

@misc{cryptoeprint:2004:050,
    author = {Lizhen Yang, Xiaoyun Wang, Dong Zheng, Kefei Chen},
    title = {Yet another attack on a password authentication scheme based on quadratic residues with parameters unknown 1},
    howpublished = {Cryptology ePrint Archive, Report 2004/050},
    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.