@misc{cryptoeprint:2012:043,
author = {Chingfang Hsu and Bing Zeng and Qi Cheng and Guohua Cui},
title = {A novel Group Key Transfer Protocol},
howpublished = {Cryptology ePrint Archive, Report 2012/043},
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.