@misc{cryptoeprint:2014:855,
author = {Rusydi H. Makarim and Cihangir Tezcan},
title = {Relating Undisturbed Bits to Other Properties of Substitution Boxes},
howpublished = {Cryptology ePrint Archive, Report 2014/855},
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.