@misc{cryptoeprint:2012:422,
author = {Mustafa \c{C}oban and Ferhat Karako\c{c} and \"{O}zkan Bozta\c{s}},
title = {Biclique Cryptanalysis of TWINE},
howpublished = {Cryptology ePrint Archive, Report 2012/422},
year = {2012},
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.