@misc{cryptoeprint:2012:190,
author = {Ding Wang and Chun-guang Ma},
title = {On the Security of an Improved Password Authentication Scheme Based on ECC},
howpublished = {Cryptology ePrint Archive, Report 2012/190},
year = {2012},
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.