The payload sent/received during the second round of a J-PAKE exchange. Each JPAKEParticipant creates and sends an instance of this payload to the other JPAKEParticipant. The payload to send should be created via JPAKEParticipant#createRound2PayloadToSend() Each JPAKEParticipant must also validate the payload received from the other JPAKEParticipant. The received payload should be validated via JPAKEParticipant#validateRound2PayloadReceived(JPakeRound2Payload)