Computer Security

A and B want to establish a secure communication channel between them. They do not care about the confidentiality of the messages being transmitted, but they do want to ensure the integrity and authenticity of the messages. Answer the following questions by drawing diagrams that show the procedures of sending and receiving messages. Assume A and B share a common key K.

a) How can they achieve their goal only with secret key cryptography?

b) How can they achieve their goal only with hash function (e.g., MD5)?

c) Can they get non-repudiation? If yes, how? If no, why?

d) Describe a way A and B can get non-repudiation. Explain your assumption and draw a diagram to show the procedure.