@misc{cryptoeprint:2007:424,
author = {Antoine Joux and David Naccache and Emmanuel Thomé},
title = {When e-th Roots Become Easier Than Factoring},
howpublished = {Cryptology ePrint Archive, Report 2007/424},
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.