@misc{cryptoeprint:2012:512,
author = {Ivan Damgard and Sarah Zakarias},
title = {Constant-Overhead Secure Computation of Boolean Circuits using Preprocessing},
howpublished = {Cryptology ePrint Archive, Report 2012/512},
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.