Assume that A and B share a long-term 256-bit AES keyK. Our key exchange protocol has twogoals: (1) let A and B agree on a new fresh session keyKsto be used for a current session, and (2)perform mutual authentication. Nb is a nonce andKsis a new session key generated by B. AssumethatKsandNbare of the same bit-length and both are always chosen at random. EK(.) denotesAES encryption of everything inside () with keyK. HM ACK(.) denotes SHA2-based HMAC ofeverything inside () using keyK Required:
What (if any) are the vulnerabilities of this protocol?

Suppose there is a relation r(a, b, c) with a b+-tree index with search keys (a, b).1. what is the worst-case cost of finding records satisfying 10 < a < 50 using this index, in terms of the number of records n1, retrieved and the height h of the tree? 2. what is the worst-case cost of finding records satisfying 10 < a < 50 and 5 < b < 10 using this index, in terms of the number of records n2 that satisfy this selection, as well as n1 and h defined above? 3. under what conditions on n1 and n2, would the index be an efficient way of finding records satisfying the condition from part (2)?