Cryptology ePrint Archive: BibTeX Citation of Report 2002/087

@misc{cryptoeprint:2002:087,
    author = {Nicolas T. Courtois},
    title = {Higher Order Correlation Attacks, XL algorithm and Cryptanalysis of Toyocrypt},
    howpublished = {Cryptology ePrint Archive, Report 2002/087},
    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.