The payload sent/received during the optional third round of a J-PAKE exchange, which is for explicit key confirmation. Each JPAKEParticipant creates and sends an instance of this payload to the other JPAKEParticipant. The payload to send should be created via JPAKEParticipant#createRound3PayloadToSend(BigInteger) Eeach JPAKEParticipant must also validate the payload received from the other JPAKEParticipant. The received payload should be validated via JPAKEParticipant#validateRound3PayloadReceived(JPakeRound3Payload, BigInteger)