@misc{cryptoeprint:2008:396,
author = {Subhamoy Maitra and Goutam Paul},
title = {Analysis of RC4 and Proposal of Additional Layers for Better Security Margin},
howpublished = {Cryptology ePrint Archive, Report 2008/396},
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.