Cryptology ePrint Archive: BibTeX Citation of Report 2013/489

@misc{cryptoeprint:2013:489,
    author = {Constantinos Patsakis and Agusti Solanas},
    title = {An Efficient Scheme for Centralized Group Key Management in  Collaborative Environments},
    howpublished = {Cryptology ePrint Archive, Report 2013/489},
    year = {2013},
    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.