(3 points) Suppose that Alice and Bob want to communicate securely using both symmetric and public-key encryption. For each of the following encryption expressions, write the corresponding decryption expression. Let K, $K_1$, $K_2$ be shared symmetric keys, P be the plaintext, and C be the ciphertext.
Alice Bob
C = E(E(P, $K_1$), $K_2$) P=
C = \{E(P, K)\} _{Bob} P=
C = [E(\{P\} _{Bob}, K)] _{Alice} P=