Eikoh Chida Yosuke Kasai Masahiro Mambo Hiroki Shizuya Spending Offline Divisible Coins with Combining Capability. 339-353 2002 conf/indocrypt/2002 INDOCRYPT http://link.springer.de/link/service/series/0558/bibs/2551/25510339.htm db/conf/indocrypt/indocrypt2002.html#ChidaKMS02