An authentication protocol using a key distribution center (KDC) is shown in figure. Each user share one and only one key with KDC. The authentication and the exchange of session key between two users happens via KDC. KDC A KDC: IDA, E(KA, [IDB, KAB] KDCB: E(KB, [IDA, KAB]D) For example, if A wants to communicate with B, he creates a session key KAB and indicates to KDC that he wants to speak to B by sending message encrypted by KA. KA is key shared between A and KDC. KDC decrypts this message and creates a new one intended for B, containing IDa and session key between A and B. This message is encrypted with the key common to B and KDC that is KB. 1- Explain why a pirate cannot pretend to be A at KDC 2- Explain why B is sure that the message comes from KDC From which attacks is this protocol not shielded thwart this type of attacks? 4- How can we improve the protocol, without increasing the number of exchanges to