@misc{cryptoeprint:2006:235,
author = {Abderrahmane Nitaj},
title = {Application of ECM to a Class of RSA keys},
howpublished = {Cryptology ePrint Archive, Report 2006/235},
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.