@misc{cryptoeprint:2009:286,
author = {Paulo Mateus and Serge Vaudenay},
title = {On Privacy Losses in the Trusted Agent Model (Abstract)},
howpublished = {Cryptology ePrint Archive, Report 2009/286},
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.