@misc{cryptoeprint:2011:541,
author = {Orr Dunkelman, Nathan Keller, Adi Shamir},
title = {Minimalism in Cryptography: The Even-Mansour Scheme Revisited},
howpublished = {Cryptology ePrint Archive, Report 2011/541},
year = {2011},
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.