@misc{cryptoeprint:2005:133,
author = {Paulo S. L. M. Barreto and Michael Naehrig},
title = {Pairing-Friendly Elliptic Curves of Prime Order},
howpublished = {Cryptology ePrint Archive, Report 2005/133},
year = {2005},
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.