@misc{cryptoeprint:2008:477,
author = {Ton van Deursen and Sasa Radomirovic},
title = {On a New Formal Proof Model for RFID Location Privacy (Extended Version)},
howpublished = {Cryptology ePrint Archive, Report 2008/477},
year = {2008},
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.