Fagen Li Masaaki Shirase Tsuyoshi Takagi On the Security of Online/Offline Signatures and Multisignatures from ACISP'06. 108-119 2008 CANS http://dx.doi.org/10.1007/978-3-540-89641-8_8 conf/cans/2008 db/conf/cans/cans2008.html#LiST08