A Low-Storage-TTP and Abuse-Free Contract Signing Protocol Based on the Schnorr Signature

A well-designed contract signing protocol should be fair, optimistic, abuse-free and efficient, which, however, cannot be realized concurrently, especially in some cases is a trade-off problem. In fact, most existing relevant protocols are difficult to guarantee abuse-freeness and efficiency, although they can often ensure fairness and optimism. To solve this problem, a new low-storage-TTP and abuse-free contract signing protocol was proposed based on the Schnorr signature. In this work, we achieve the properties of fairness and optimism through introducing a dedicated off-line trusted third party (TTP). In order to ensure abuse-freeness, we introduce the proxy key scheme. To improve efficiency, our protocol implements a new property-low-storage-TTP which greatly reduces the TTP's burden by integrating with symmetric encryption. Theoretical analysis and comparative analysis show that the storage of TTP reduce by more than 50% while ensuring fairness, optimism and abuse-freeness in our protocol.