@misc{cryptoeprint:2015:516,
author = {Brice Minaud and Patrick Derbez and Pierre-Alain Fouque and Pierre Karpman},
title = {Key-Recovery Attacks on ASASA},
howpublished = {Cryptology ePrint Archive, Report 2015/516},
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.