@misc{cryptoeprint:2011:100,
author = {Guangdong Yang and Shaohua Tang and Li Yang},
title = {A Novel Group Signature Scheme Based on MPKC},
howpublished = {Cryptology ePrint Archive, Report 2011/100},
year = {2011},
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.