Xinyi Huang Willy Susilo Yi Mu Futai Zhang Breaking and Repairing Trapdoor-Free Group Signature Schemes from Asiacrypt'2004. 71-74 2007 22 J. Comput. Sci. Technol. 1 http://dx.doi.org/10.1007/s11390-007-9008-8 db/journals/jcst/jcst22.html#HuangSMZ07