5. (a) What is a collision-resistant hash function? (b) Is the checksum function collison-resistant? Explain your answer. Provide a concise description of a digital signature protocol (in the sends this, Bob sends that...). (c) (d) What is the role of collision-resistant hash functions in establishing of the protocol against malicious attacks? (4 marks) (4 marks) form Alice (6 marks) robustness (6 marks)