2. (10 points) Alice and Bob share the same pair of symmetric encryption algorithms, E and D. Also, they share the symmetric encryption key K. Suppose Alice wants to send a message M to Bob. Design an encryption scheme that will protect the confidentiality of M and prevent the message tampering during the transmission. (Hint: You may need to use cryptographic hash HASH to create a digest for some messages. For example, you can generate a digest for message D with HASH(D). You can concatenate two messages by using concatenate operator "II". For example, you can concatenate two message A and B with AB). a) (5 points) Write down the message format sent from Alice to Bob. b) (5 points) Describe how does Bob decrypt the received message and verify the authenticity of the message