Question

Alice wants to send a message to Bob. But Eve can intercept and read the messages. Whereas, Mallory can modify or forge the messages. Moreover, once Bob sends a message to Alice, he can sometimes deny it. Therefore, what security measures should Alice take for the following:

• To ensure message confidentiality.
• To ensure non-repudiation.
• To ensure message integrity.
• How can the secret key be securely shared between Alice and Bob.

Answer 1

Alice should use encryption for message confidentiality, digital signatures for non-repudiation, and hashing for message integrity. For the secure key exchange between Alice and Bob, the Diffie-Hellman algorithm can be used.

Step-by-step explanation:

To ensure message confidentiality, Alice should use encryption, such as symmetric or asymmetric encryption, which scrambles the message content so that only Bob, with the correct key, can decrypt and read it. For non-repudiation, digital signatures should be implemented. Bob can sign the message with his private key, and Alice can verify it with his public key, providing proof that Bob sent the message. To guarantee message integrity, Alice and Bob can use hashing algorithms along with digital signatures. A hash function creates a unique fixed-size string from a message. Bob can hash the message before sending it to Alice, and Alice can re-hash the received message to compare hashes, ensuring that the message has not been altered during transmission.

For the secure sharing of a secret key between Alice and Bob, they can use a key exchange algorithm like Diffie-Hellman, which allows them to securely exchange cryptographic keys over an insecure communication channel.