@misc{cryptoeprint:2001:080,
author = {Eric Filiol and Caroline Fontaine},
title = {COS Ciphers are not "extremely weak"! - The Design Rationale of COS Ciphers},
howpublished = {Cryptology ePrint Archive, Report 2001/080},
year = {2001},
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.