In this paper

we reviewed the art of e-cash in brief

and improved the Brands' e-cash system based on the restrictive blind signature.In our new e-cash system

the withdrawal date and expiry date

prescribed by the bank are embedded in the withdrawn e-cash.Users cannot alter these information later

the bank only needs to keep all used and undue e-cash in his database to trace the double-spender.Thus it reduces the storage level and improves the querying efficiency of the bank to detect double-spending.