Ron Steinfeld Josef Pieprzyk Huaxiong Wang How to Strengthen Any Weakly Unforgeable Signature into a Strongly Unforgeable Signature. 357-371 2007 conf/ctrsa/2007 CT-RSA http://dx.doi.org/10.1007/11967668_23 db/conf/ctrsa/ctrsa2007.html#SteinfeldPW07