@misc{cryptoeprint:2008:153,
author = {Clemens Heuberger},
title = {Redundant $\tau$-adic Expansions II: Non-Optimality and Chaotic Behaviour},
howpublished = {Cryptology ePrint Archive, Report 2008/153},
year = {2008},
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.