Cryptology ePrint Archive: BibTeX Citation of Report 2004/090

@misc{cryptoeprint:2004:090,
    author = {Ratna Dutta and Rana Barua and and Palash Sarkar},
    title = {Provably Secure Authenticated Tree Based Group Key Agreement Protocol},
    howpublished = {Cryptology ePrint Archive, Report 2004/090},
    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.