@misc{cryptoeprint:2004:337,
author = {Wu Wenling and Zhang Wentao and Lin Dongdai },
title = {Security on Generalized Feistel Scheme with SP Round Function},
howpublished = {Cryptology ePrint Archive, Report 2004/337},
year = {2004},
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.