Cryptology ePrint Archive: BibTeX Citation of Report 2004/115

@misc{cryptoeprint:2004:115,
    author = {Junghyun Nam, Sungduk Kim, Seungjoo Kim, and Dongho Won},
    title = {Provably-Secure and Communication-Efficient Scheme for Dynamic Group Key Exchange},
    howpublished = {Cryptology ePrint Archive, Report 2004/115},
    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.