@misc{cryptoeprint:2004:356,
author = {Ondrej Mikle},
title = {Practical Attacks on Digital Signatures Using MD5 Message Digest},
howpublished = {Cryptology ePrint Archive, Report 2004/356},
year = {2004},
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.