Avoiding loss of fairness owing to process crashes in fair data exchange protocols

Fair exchange between two or more potentially mutually distrusted parties has been identified as an important issue in electronic commerce. However, the correctness (fairness) of the existing fair exchange protocols that use a Trusted Third Party (TTP) is based on the assumption that during an exchange there are no failures at any of the local systems involved in the exchange, which is too strong in many situations. This paper points out that (1) system failures could cause loss of fairness, and (2) existing fair exchange protocols that use TTPs cannot ensure fairness in presence of system failures. We present a systematic way to develop such data exchange systems that can recover from system failures without losing fairness. We identify a set of fairness loss risks caused by local system failures. We identify a fault tolerance correctness criteria for fair data exchange, denoted fairness-lossless recoverability. A fairness-lossless recoverable fair exchange system is immune from the set of fairness loss risks. Standard message logging approaches are then studied and extended to achieve fairness-lossless recoverability with good performance.