@misc{cryptoeprint:2009:516,
author = {Axel Poschmann},
title = {Lightweight Cryptography - Cryptographic Engineering for a Pervasive World},
howpublished = {Cryptology ePrint Archive, Report 2009/516},
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.