Yair Frankel Yiannis Tsiounis Moti Yung Fair Off-Line e-cash Made Easy. 257-270 http://link.springer.de/link/service/series/0558/bibs/1514/15140257.htm 1998 conf/asiacrypt/1998 ASIACRYPT db/conf/asiacrypt/asiacrypt98.html#FrankelTY98