@misc{cryptoeprint:2010:066,
author = {Bozhan Su and Wenling Wu and Lei Zhang and Yanjun Li},
title = {Some Observations on TWIS Block Cipher},
howpublished = {Cryptology ePrint Archive, Report 2010/066},
year = {2010},
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.