@misc{cryptoeprint:2004:179,
author = {Sherman S.M. Chow and Lucas C.K. Hui and S.M. Yiu},
title = {Identity Based Threshold Ring Signature},
howpublished = {Cryptology ePrint Archive, Report 2004/179},
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.