Cryptology ePrint Archive: BibTeX Citation of Report 2009/609

@misc{cryptoeprint:2009:609,
    author = {Dang Nguyen Duc and Kwangjo Kim},
    title = {Grouping-Proof Protocol for RFID Tags: Security Definition and Scalable Construction},
    howpublished = {Cryptology ePrint Archive, Report 2009/609},
    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.