Analyze the following scheme and answer the questions .

a. What security objectives this scheme provide?

b. What pair of keys are used to ensure confidentiality

c. What pair of keys are used to ensure authentication of the sender ?

d. Suppose a hacker be able to intercept E(PR_a,M), can he retrieve M ?

e. Can you simplify the scheme, if we do not need confidentiality ? Only the authentication of the sender is needed.

E E D D M PRA E(Pra, M) PU, E(PU), E(PR, M) PRE(PR, M) PUA