@misc{cryptoeprint:2012:113,
author = {Bart Mennink},
title = {On the Collision and Preimage Security of MDC-4 in the Ideal Cipher Model},
howpublished = {Cryptology ePrint Archive, Report 2012/113},
year = {2012},
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.