@misc{cryptoeprint:2012:495,
author = {Alfredo De Santis and Moti Yung},
title = {"Metaproofs" (and their Cryptographic Applications)},
howpublished = {Cryptology ePrint Archive, Report 2012/495},
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.