@misc{cryptoeprint:2013:439,
author = {Peter Pessl and Michael Hutter},
title = {Pushing the Limits of SHA-3 Hardware Implementations to Fit on RFID},
howpublished = {Cryptology ePrint Archive, Report 2013/439},
year = {2013},
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.