@misc{cryptoeprint:2008:499,
author = {Subhamoy Maitra and Goutam Paul and Shashwat Raizada},
title = {Some Observations on HC-128},
howpublished = {Cryptology ePrint Archive, Report 2008/499},
year = {2008},
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.