@misc{cryptoeprint:2007:001,
author = {Laura Hitt},
title = {Families of genus 2 curves with small embedding degree},
howpublished = {Cryptology ePrint Archive, Report 2007/001},
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.