Cryptology ePrint Archive: BibTeX Citation of Report 2002/152

@misc{cryptoeprint:2002:152,
    author = {Jorge Nakahara Jr and Bart Preneel and Joos Vandewalle},
    title = {A note on Weak Keys of PES, IDEA and some Extended Variants},
    howpublished = {Cryptology ePrint Archive, Report 2002/152},
    year = {2002},
    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.