We address the multicast stream authentication problem when the communication channel is under the control of an opponent who can drop, reorder or inject data. In such a network model, packet overhead and computing efficiency are important parameters to be taken into account when designing a multicast authentication protocol. Our construction will exhibit three main advantages. First, our packet overhead will only be a few hashes long. Second, we will exhibit a number of signature verifications to be performed by the receivers which will turn to be
(1). Third, every receiver will still be able to recover all the data packets emitted by the sender despite losses and injections occurred during the transmission of information.