2) Merkle Hash Tree and its applications: [15 Points] Suppose a sender S uses this Merkle hash tree to authenticate these messages to a receiver R. a) How would one authenticate message M4? Write which elements must be transmitted from sender to the receiver [3pt], and write the correct verification equation as in slides. [2 pt] b) Merkle hash trees have an additional level of hash in the leaves. Why? [2 pt] c) What are two necessary conditions for a set of data to be authenticated by Merkle-tree? [4 pt] d) Describe how Merkle-hash trees are used for memory integrity protection in computer systems and in Cryptocurrencies. [4 pt]