@misc{cryptoeprint:2009:168,
author = {Michael A. Halcrow and Niels Ferguson},
title = {A Second Pre-image Attack Against Elliptic Curve Only Hash (ECOH)},
howpublished = {Cryptology ePrint Archive, Report 2009/168},
year = {2009},
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.