Suppose Alice wants to send an e-mail to Bob. Bob has a public-private key pair

Question

Suppose Alice wants to send an e-mail to Bob. Bob has a public-private key pair (KB+, KB–), and Alice has Bob’s certificate. But Alice does not have a public, private key pair. Alice and Bob (and the entire world) share the same hash function H (.). a. In this situation, is it possible to design a scheme so that Bob can verify that Alice created the message? If so, show how with a block diagram for Alice and Bob. b. Is it possible to design a scheme that provides confidentiality for sending the message from Alice to Bob? If so, show how with a block diagram for Alice and Bob.

Explanation / Answer

(A) No,without a public-private key pair ,Bob cannot verify that Alice created the message

(B) Yes, Alice simply encrypts the message with Bob’s public key and sends the encrypted message to Bob

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