Recall the “perfect forward secrecy” refers to the event tha…
Recall the “perfect forward secrecy” refers to the event that even if the attacker was able to record the complete conversations (that is, all the messages including the session establishment and encrypted data been exchanged) between Alice and Bob, and later compromise both Alice and Bob and obtained all their secrets, the attacker is still unable to infer the content of the previously recorded message. 4 scenarios are described in the following. For each scenario, first answer if it has the perfect forward secrecy property, and then briefly explain your reason. For example, if your answer is that a scenario does have perfect forward secrecy, you should explain that why the attacker, with secrets from both Alice and Bob, is unable to decrypt the previously recorded message; if your answer is a scenario does not have perfect forward secrecy, you should explain how will the attacker decrypt the previously recorded message to recover the plaintext. Alice generates a secret session key, Alice uses Bob’s public key encrypt the session key and sends it to Bob. Alice and Bob uses this session key for data exchange and both delete this session key from their memory when the session finishes. Alice generates a pair of public-private key. Alice signs the public key using her private key and send it to Bob. Bob generates a secret session key, uses this public key to encrypt the session key and sends it to Alice, and Alice decrypts this message using the corresponding private key. Alice and Bob use this secret session key for data exchange and both delete from their memory the session key, and the public-private key pair when when the session finishes. Alice generates a secret session key, she uses her private key to sign the session and send it to Bob. Alice and Bob uses this secret session key for data exchange and both delete the session key from their memory when the session finishes. Alice and Bob do a standard Diffie Hellman exchange based on two random value they generated separately. And they use the secret obtained by the end of Diffie Hellman exchange for data exchange. Both Alice and Bob delete these random values from their memory when the session finishes.