@misc{cryptoeprint:2011:268,
author = {Raja Zeshan Haider},
title = {Birthday Forgery Attack on 128-EIA3 Version 1.5},
howpublished = {Cryptology ePrint Archive, Report 2011/268},
year = {2011},
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.