@misc{cryptoeprint:2007:389,
author = {Dragos Florin Ciocan and Salil Vadhan},
title = {Interactive and Noninteractive Zero Knowledge Coincide in the Help Model},
howpublished = {Cryptology ePrint Archive, Report 2007/389},
year = {2007},
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.