@misc{cryptoeprint:2009:013,
author = {Yehuda Lindell},
title = {Comparison-Based Key Exchange and the Security of the Numeric Comparison Mode in Bluetooth v2.1},
howpublished = {Cryptology ePrint Archive, Report 2009/013},
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.