Blind, Auditable Membership Proofs

  • Authors:
  • Tomas Sander;Amnon Ta-Shma;Moti Yung

  • Affiliations:
  • -;-;-

  • Venue:
  • FC '00 Proceedings of the 4th International Conference on Financial Cryptography
  • Year:
  • 2000

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Abstract

Auditability is an important property in financial systems and architectures. Here we define the primitive of "blind auditable membership proof" (BAMP) which combines public auditability with privacy (i.e. user anonymity). In particular, one can use it as an auditable alternative to a "blind signature" component in unconditionally anonymous payment systems and in other systems requiring anonymity. We show that BAMP can be implemented quite efficiently (namely, without resorting to general zero-knowledge proofs of NP statements, which, in general, merely indicates plausibility).We then build an anonymous off-line payment system based on the implementation of BAMP. The system has the property that its security against counterfeiting relies on the integrity of a public (auditable) database and not on the secrecy of privately held keys. The system strongly defends against blackmailing and bank robbery attacks, in the same way the system in [21] does. However, the current system is a significant step towards practicality since, unlike the previous system, first, it does not use general protocols for zero knowledge proofs for NP, and second, the cost of the payment protocol is independent of the number of total coins withdrawn.