@misc{cryptoeprint:2006:398,
author = {Amir Herzberg and Igal Yoffe},
title = {The Layered Games Framework for Specifications and Analysis of Security Protocols},
howpublished = {Cryptology ePrint Archive, Report 2006/398},
year = {2006},
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.