An exemplary optimistic protocol for a two-party transaction includes a setup sub-protocol that includes an authorized Diffie-Hellman key agreement, an exchange sub-protocol that includes 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 that includes 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. Other exemplary methods, systems, etc., are also disclosed.