@misc{cryptoeprint:2013:210,
author = {Arno Mittelbach},
title = {Cryptophia's Short Combiner for Collision-Resistant Hash Functions},
howpublished = {Cryptology ePrint Archive, Report 2013/210},
year = {2013},
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.