@misc{cryptoeprint:2002:149,
author = {Nicolas T. Courtois},
title = {About Filliol's Observations on DES, AES and Hash Functions (draft)},
howpublished = {Cryptology ePrint Archive, Report 2002/149},
year = {2002},
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.