@misc{cryptoeprint:2003:065,
author = {Mihir Bellare and Tadayoshi Kohno},
title = {Hash Function Balance and its Impact on Birthday Attacks},
howpublished = {Cryptology ePrint Archive, Report 2003/065},
year = {2003},
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.