Cryptology ePrint Archive: BibTeX Citation of Report 2011/234

@misc{cryptoeprint:2011:234,
    author = {Debiao He},
    title = {Comments on a secure dynamic ID-based remote user authentication scheme for multi-server environment using smart cards},
    howpublished = {Cryptology ePrint Archive, Report 2011/234},
    year = {2011},
    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.