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6. Certificates and PKI. (10 points) In this question, we assume that all public keys are known to everyone. Alice attempts to send a large file to Bob. Alice wants to ensure that only Bob sees the content. They followed a protocol as below to exchange the file: a) Alice and Bob use the Diffie-Hellman key exchange to generate a session key K. b) Alice encrypts the file F with Bob's public key to obtain F. c) Alice encrypts F with K to obtain F. d) Alice sends F to Bob. 6.2. Is this protocol efficient? If it is not efficient, please explain the reasons