Cryptology ePrint Archive: BibTeX Citation of Report 2007/205

@misc{cryptoeprint:2007:205,
    author = {Kazumaro Aoki and Jens Franke and Thorsten Kleinjung and Arjen Lenstra and Dag Arne Osvik},
    title = {A kilobit special number field sieve factorization},
    howpublished = {Cryptology ePrint Archive, Report 2007/205},
    year = {2007},
    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.