Which cryptographic mechanism provides sender authentication and message integrity by encrypting a hash with the sender's private key?

Which cryptographic mechanism provides sender authentication and message integrity by encrypting a hash with the sender's private key?

• A. Hash Function
• B. Public Key Infrastructure
• C. Message Authentication Code
• D. Digital Signature

Answer: (D)

A digital signature is the mechanism being described. It involves taking a hash of the message and encrypting that hash with the sender’s private key. This creates a signature that proves the message came from the holder of that private key (sender authentication) and that the message hasn’t been altered since it was signed (message integrity). The recipient can verify by decrypting the signature with the sender’s public key and comparing the result to a fresh hash of the received message. This process also supports non-repudiation, assuming the private key remains secure. By contrast, a hash function alone only checks integrity, a MAC would rely on a shared secret (not a private key), and PKI is the framework that manages keys and certificates rather than the signature mechanism itself.