An Optimistic NBAC-Based Fair Exchange Method for Arbitrary Items

Fair exchange protocols are important in realizing safe electronic commerce. In particular, optimistic fair exchange protocols, which involve a trusted third party only when mutual communication between exchanging parties fails, are the most promising development because of their efficiency. Unfortunately, however, existing optimistic protocols place restrictions on the items that can be exchanged, i.e., at least one item must be a “strongly generatable” item such as a digital signature. Without this requirement, only weak fairness that requires (expensive) external dispute resolution processes (e.g. trials in court) after exchange failure can be assured. This paper proposes a novel fair exchange method that enables parties to fairly exchange arbitrary items in an optimistic manner. This is achieved by realizing an optimistic non-blocking atomic commitment (NBAC) protocol between two smartcards and adapting the known result that fair exchange can be reduced to NBAC among trusted processes.