@misc{cryptoeprint:2007:181,
author = {Kwang Ho Kim and So In Kim},
title = {A New Method for Speeding Up Arithmetic on Elliptic Curves over Binary Fields},
howpublished = {Cryptology ePrint Archive, Report 2007/181},
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.