@misc{cryptoeprint:2006:355,
author = {Boaz Barak and Manoj Prabhakaran and Amit Sahai},
title = {Concurrent Non-Malleable Zero Knowledge},
howpublished = {Cryptology ePrint Archive, Report 2006/355},
year = {2006},
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.