@misc{cryptoeprint:2004:292,
author = {Ruishan Zhang and Kefei Chen},
title = {Asynchronous Proactive RSA},
howpublished = {Cryptology ePrint Archive, Report 2004/292},
year = {2004},
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.