Cryptology ePrint Archive: BibTeX Citation of Report 2005/237

@misc{cryptoeprint:2005:237,
    author = {Henri Gilbert and Matt Robshaw and Herve Sibert},
    title = {An Active Attack Against HB+ - A Provably Secure Lightweight Authentication Protocol},
    howpublished = {Cryptology ePrint Archive, Report 2005/237},
    year = {2005},
    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.