@misc{cryptoeprint:1999:023,
author = {Cynthia Dwork, Moni Naor and Amit Sahai},
title = {Concurrent Zero-Knowledge},
howpublished = {Cryptology ePrint Archive, Report 1999/023},
year = {1999},
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.