@misc{cryptoeprint:2009:157,
author = {Peter Birkner and Nicolas Thériault},
title = {Efficient Halving for Genus 3 Curves over Binary Fields},
howpublished = {Cryptology ePrint Archive, Report 2009/157},
year = {2009},
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.