Electronic contract signing allows two potentially dis-trustful parties to digitally sign an electronic document "simultaneously" across a network. Existing solutions for electronic contract signing either require the involvement of a trusted third party (TTP), or are complex and expensive in communication and computation. In this paper we propose an electronic contract signing protocol between two parties with the following advantages over existing solutions: 1) it is practical and scalable due to its simplicity and high efficiency; 2) it does not require any trusted third party as the mediator; and 3) it guarantees fairness between the two signing parties. We achieve these properties by employing a trustworthy timestamping service in our protocol, where the timestamping service can be either centralized or decentralized. We also provide a detailed analysis on security and performance of our scheme.
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