Question 5 (20 points) Alice wants to communicate with Bob using symmetric-key cryptography (eg DES) with a session-key Ks. In the lectures we leaned how public-key cryptography (eg RSA) can be used to distribute a session key Ks from Alice to Bob. Suppose the private keys of Alice and Bob are ka and ke, while the public keys are KA and Kg. Also, we assume that Alice and Bob have got each other's public key through a trusty method. 1. What is the main advantage of first distributing a session key and then using symmetric-key cryptography rather than using public-key cryptography techniques for the whole communication? (5 points) 2. Draw a diagram that shows the message exchange between Alice and Bob which achieves this, ie., using the public-key cryptography to distribute a symmetrie session-key (7 points) 3. Describe the difference between confidentiality and integrity (using digital signature) using public-key cryptography. (8 points)