@misc{cryptoeprint:2009:179,
author = {Hongbo Yu and Xiaoyun Wang},
title = {Near-Collision Attack on the Compression Function of Dynamic SHA2},
howpublished = {Cryptology ePrint Archive, Report 2009/179},
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.