Correct. C. His own private key. Page 3065, CEH v11 "Sender sends hash code using his PRIVATE key"

Asymmetric Encryption uses two distinct, yet related keys. One key, the Public Key, is used for encryption and the other, the Private Key, is for decryption. As implied in the name, the Private Key is intended to be private so that only the authenticated recipient can decrypt the message.

Encryption. Not signing

ChatGPT answer: Correct answer: A. Alice's public key Explanation: Bob wants to ensure that Alice can check whether his message has been tampered with. To achieve this, he encrypts the checksum of the message using asymmetric cryptography. In asymmetric cryptography, there are two keys: a public key and a private key. The public key is used for encryption, and the private key is used for decryption. Bob uses Alice's public key for encryption: Bob wants Alice to be able to decrypt and verify the checksum. In asymmetric cryptography, anything encrypted with the public key can only be decrypted with the corresponding private key. Therefore, by encrypting the checksum with Alice's public key, only Alice (who possesses the corresponding private key) can decrypt and verify it.

A is the correct choice. He uses Alice's public key to encrypt the message and Alice use her own private key to decrypt the message.

Bob uses Alice's public key to encrypt the checksum. This is a common practice in asymmetric cryptography. Bob uses Alice's public key for encryption because only Alice, with access to the corresponding private key, can decrypt the message. This ensures that only Alice can verify the integrity of the message by decrypting the checksum and comparing it to a newly calculated checksum of the received message. Using Alice's public key for encryption adds an extra layer of security to ensure that the checksum is only accessible to the intended recipient.

His own private key

Encrypt the message -> Alice's public key Encrypt the checksum -> His own private key

Simply put, what is required is to ensure that the message has not been tampered with. What is correct is that the message is signed by the sender, which is bob by its public key. Method a is confidential, that is, the message can only be opened by the recipient. If the answer is C

The correct opción is A.

The correct option is C C. His own private key

The correcto option is A. Alice's public key. If you choose the C, Alice can't read the message!

Bob will digitally sign the message using his private key. Bob will encrypt the message using Alice's public key - So only Alice can decrypt the message. The question talks about encryption. Hence Answer is A - Alice's public key

ambigious question, if use PGP is A, not is C

A. Sign a message: sender's privatek-> senders's publick encrip. a message: receiver's publick-> receivers's private Here are "encripting", they never say "sign".

The answer is A, Creating a checksum of a message does not equate to signing it. Bob just want Alice to be able to check if the message is has been tampered with. He does not want to sign it to proof that he is the sender of the message.

I think the question is inferring NonRepudiation over Confidentiality. The question states "check whether his message has been tampered with". Anyone can encrypt with Alice's public key and impersonate Bob so although that method would ensure full confidentiality, it could not verify it was actually his message being sent. Encrypting using his private key ensures that it was actually sent by him, although anyone would be able to be decrypt it using his public key, not just Alice. The question doesn't mention this as being a requirement though. The only way to ensure the message was sent by him and not tampered with is by encrypting using his private key.