@misc{cryptoeprint:2015:761,
author = {William Diehl},
title = {Implementation of the SCREAM Tweakable Block Cipher in MSP430 Assembly Language},
howpublished = {Cryptology ePrint Archive, Report 2015/761},
year = {2015},
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.