This paper describes a modular interface, called group ecash, that provides a rich form of electronic cash with escrow and shows how it can be implemented by most kinds of group signatures. The interface is shown to provide a broad range of basic guarantees including anonymity, divisibility, unlinkability, unreusability, refundability, customer unforgeability, tracing of owners and coins, framing-freeness, and protection against blackmail and bank robbery. Intrinsic properties of group signatures also make it easy to implement additional features such as revocation, protection against bank forgery and unavailability, and tracing of bank robbers. These additional features are unavailable or entail complicating extensions in other approaches. We analyze the performance of an implementation of group ecash based on a specific group signature scheme.

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