@misc{cryptoeprint:2014:664,
author = {William R. Trost and Guangwu Xu},
title = {On the Optimal Pre-Computation of Window $\tau$NAF for Koblitz Curves},
howpublished = {Cryptology ePrint Archive, Report 2014/664},
year = {2014},
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.