Cryptology ePrint Archive: BibTeX Citation of Report 2004/234

@misc{cryptoeprint:2004:234,
    author = {Zuo-Wen Tan and Zhuo-Jun Liu},
    title = {On the security of some nonrepudiable threshold proxy signature schemes with known signers},
    howpublished = {Cryptology ePrint Archive, Report 2004/234},
    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.