Cryptology ePrint Archive: BibTeX Citation of Report 2011/143

@misc{cryptoeprint:2011:143,
    author = {Romain Cosset and Damien Robert},
    title = {Computing $(\ell,\ell)$-isogenies in polynomial time on Jacobians of genus~$2$ curves},
    howpublished = {Cryptology ePrint Archive, Report 2011/143},
    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.