@misc{cryptoeprint:2012:315,
author = {Teng Guo and Feng Liu and ChuanKun Wu and YoungChang Hou},
title = {Using Variance to Analyze Visual Cryptography Schemes},
howpublished = {Cryptology ePrint Archive, Report 2012/315},
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.