Cryptology ePrint Archive: BibTeX Citation of Report 2009/300

@misc{cryptoeprint:2009:300,
    author = {M. Choudary Gorantla and Colin Boyd and Juan Manuel Gonz\`alez Nieto},
    title = {Universally Composable Contributory Group Key Exchange},
    howpublished = {Cryptology ePrint Archive, Report 2009/300},
    year = {2009},
    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.