@misc{cryptoeprint:2010:538,
author = {Dmitry Khovratovich and Ivica Nikolic and Christian Rechberger},
title = {Rotational Rebound Attacks on Reduced Skein},
howpublished = {Cryptology ePrint Archive, Report 2010/538},
year = {2010},
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.