@misc{cryptoeprint:2005:163,
author = {Jonathan Katz and Ji Sun Shin},
title = {Modeling Insider Attacks on Group Key-Exchange Protocols},
howpublished = {Cryptology ePrint Archive, Report 2005/163},
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.