Cryptology ePrint Archive: BibTeX Citation of Report 1999/009

@misc{cryptoeprint:1999:009,
    author = {Satoshi Hada and Toshiaki Tanaka},
    title = {On the Existence of	3-Round Zero-Knowledge Protocols},
    howpublished = {Cryptology ePrint Archive, Report 1999/009},
    year = {1999},
    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.