The invention is directed to an optimistic protocol (200) for a two-party transaction, the optimistic protocol comprising: a setup sub-protocol (210) that comprises an authorized Diffie-Hellman key agreement; an exchange sub-protocol (220) that comprises sending a certificate from a sending party to a receiving party and sending a receipt from the receiving party to the sending party; and a dispute sub-protocol (230) that comprises a dispute resolution mechanism for resolving disputes between the sending party and the receiving party due to sending of an invalid certificate, due to sending an invalid receipt, or due to abortion of the exchange sub-protocol (220).
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