Cryptology ePrint Archive: BibTeX Citation of Report 2006/261

@misc{cryptoeprint:2006:261,
    author = {Frederic Didier},
    title = {Using Wiedemann's algorithm to compute the immunity against algebraic and fast algebraic attacks},
    howpublished = {Cryptology ePrint Archive, Report 2006/261},
    year = {2006},
    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.