Liqun Chen Matthias Enzmann Ahmad-Reza Sadeghi Markus Schneider 0002 Michael Steiner A Privacy-Protecting Coupon System. 93-108 2005 conf/fc/2005 Financial Cryptography http://dx.doi.org/10.1007/11507840_12 db/conf/fc/fc2005.html#ChenESSS05