Cryptology ePrint Archive: BibTeX Citation of Report 2011/172

@misc{cryptoeprint:2011:172,
    author = {T.V. Laptyeva and  S. Flach and K. Kladko},
    title = {The weak password problem: chaos, criticality, and encrypted p-CAPTCHAs},
    howpublished = {Cryptology ePrint Archive, Report 2011/172},
    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.