@misc{cryptoeprint:2009:267,
author = {Stéphanie Delaune and Steve Kremer and Olivier Pereira},
title = {Simulation based security in the applied pi calculus},
howpublished = {Cryptology ePrint Archive, Report 2009/267},
year = {2009},
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.