@misc{cryptoeprint:2014:642,
author = {Shoni Gilboa and Shay Gueron },
title = {Balanced permutations Even-Mansour ciphers},
howpublished = {Cryptology ePrint Archive, Report 2014/642},
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.