@misc{cryptoeprint:2005:416,
author = {Kenneth G. Paterson and Arnold K.L. Yau},
title = {Cryptography in Theory and Practice: The Case of Encryption in IPsec},
howpublished = {Cryptology ePrint Archive, Report 2005/416},
year = {2005},
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.