@misc{cryptoeprint:2012:049,
author = {Yu Sasaki and Lei Wang},
title = {2-Dimension Sums: Distinguishers Beyond Three Rounds of RIPEMD-128 and RIPEMD-160},
howpublished = {Cryptology ePrint Archive, Report 2012/049},
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.