@misc{cryptoeprint:2015:028,
author = {Jeremy Maitin-Shepard},
title = {Optimal software-implemented Itoh--Tsujii inversion for GF($2^m$)},
howpublished = {Cryptology ePrint Archive, Report 2015/028},
year = {2015},
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.