@misc{cryptoeprint:2010:062,
author = {Bozhan Su and Wenling Wu and Wentao Zhang},
title = {Differential Cryptanalysis of SMS4 Block Cipher},
howpublished = {Cryptology ePrint Archive, Report 2010/062},
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.