How is the integrity of a digital signature guaranteed?

• A. By using a shared secret key
• B. By encrypting the message with the creator's private key
• C. By hashing the public key
• D. By a complex algorithm only

Answer: (B)

The integrity of a digital signature is guaranteed by the process of encrypting the hash of the message with the creator's private key. When a sender wants to sign a message, they first compute a hash of the message, which creates a fixed-size string that uniquely represents the contents of the message. This hash is then encrypted using the sender's private key, producing the digital signature.

This method ensures that any alteration to the content of the message after it has been signed will result in a different hash value when the message is re-hashed. When the recipient receives the signed message, they can use the sender's public key to decrypt the signature back into the hash value. They can then hash the received message themselves and compare the two hash values. If they match, it confirms that the message has not been tampered with, thus ensuring its integrity.

Utilizing a shared secret key focuses on symmetric encryption and does not provide the same level of integrity verification as public key infrastructure, while hashing the public key lacks relevance to the signature's integrity. Relying solely on a complex algorithm does not address the fundamental principle of signature verification and the role of keys involved in ensuring integrity.