@misc{cryptoeprint:2007:050,
author = {Vlastimil KLIMA},
title = {Special block cipher family DN and new generation SNMAC-type hash function family HDN},
howpublished = {Cryptology ePrint Archive, Report 2007/050},
year = {2007},
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.