Secure and Efficient Agreement Signing Atop Blockchain and Decentralized Identity

In recent years, we have witnessed an exorbitant growth of online interactions, especially during the pandemic of COVID-19, which requires diversified digital agreements in different application scenarios. In essence, multi-party agreement signing (MPAS) can be reckoned as a special case of the multi-party fair exchange (MPFE) for signatures over a digital agreement. However, such general MPAS protocols have not seen wide adoptions in practice, possibly due to the lack of incentives to maintain the signing platform. Practically, monetary-incentivized enterprises exist to act as a trusted third party (TTP) and provide signing services. However, such an agreement signing flow still suffers from certain limitations in terms of insecure and inefficient operations. To this end, we propose a secure and efficient framework for multi-party agreement signing based on decentralized identity, blockchain and decentralized storage network (DSN). The framework consists of two subsystems where the identity subsystem contains an extensible three-tier user identity model atop decentralized identity, and the agreement signing subsystem, empowered by the identity subsystem, DSN and several novel designs, achieves security and efficiency design goals. For the convenience of explanation, we suppose that a centralized signing service provider (SSP) is properly involved, i.e., sensitive information is still protected against the SSP, and acts as a TTP to ensure the crucial properties such as fairness and coordinate the signing activities. Our design is also compatible with other methods, e.g., ensuring fairness via blockchain, which removes the single point of failure of SSP. We prototype the framework and the performance evaluation shows effectiveness and efficiency.