Cryptology ePrint Archive: BibTeX Citation of Report 2004/027

@misc{cryptoeprint:2004:027,
    author = {Joseph K. Liu and Victor K. Wei and Duncan S. Wong},
    title = {Linkable Spontaneous Anonymous Group Signature for Ad Hoc Groups},
    howpublished = {Cryptology ePrint Archive, Report 2004/027},
    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.