Cryptology ePrint Archive: BibTeX Citation of Report 2009/331

@misc{cryptoeprint:2009:331,
    author = {L. Chen and P. Morrissey and N.P. Smart and B. Warinschi},
    title = {Security Notions and Generic Constructions for Client Puzzles},
    howpublished = {Cryptology ePrint Archive, Report 2009/331},
    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.