@misc{cryptoeprint:2015:172,
author = {Aria Shahverdi and Mostafa Taha and Thomas Eisenbarth},
title = {Silent Simon: A Threshold Implementation under 100 Slices},
howpublished = {Cryptology ePrint Archive, Report 2015/172},
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.