@misc{cryptoeprint:2012:369,
author = {Shi Bai and Emmanuel Thom\'e and Paul Zimmermann},
title = {Factorisation of RSA-704 with CADO-NFS},
howpublished = {Cryptology ePrint Archive, Report 2012/369},
year = {2012},
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.