Some Improvements on Recoverable E-cash

When the E-cash file being destroyed for some unexpected error, we cannot expect waiting for the recovery of the file, but improve the design of E-cash system such that the bank can compute the amount of E-cash the user really lost. Recoverability and untraceability (anonymous) are two obviously conflicting properties. If we give up untraceability, we can compute the lost E-cash by computing the difference of the withdrawn and deposit amount of the user by recording all the transaction activities in a large database, then the bank can recover the lost E-cash for the user. It is obviously unfeasible for the complexity of storage. Shoemakers proposed an E-cash system which contains recovery but it´s an on-line system. Joseph proposed an off-line E-cash system which possesses both properties of recovery and Untraceability, but it has many problems also, we analyze the problems and propose a few points of view of designing Recoverable E-cash.