@misc{cryptoeprint:2014:592,
author = {Michael Hutter and Peter Schwabe},
title = {Multiprecision multiplication on AVR revisited},
howpublished = {Cryptology ePrint Archive, Report 2014/592},
year = {2014},
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.