@misc{cryptoeprint:2007:182,
author = {Yevgeniy Dodis and Pil Joong Lee and Dae Hyun Yum},
title = {Optimistic Fair Exchange in a Multi-user Setting},
howpublished = {Cryptology ePrint Archive, Report 2007/182},
year = {2007},
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.