Which cryptographic method provides authenticity and non-repudiation using a public-key approach?

• A. MAC (Message Authentication Code)
• B. Digital Signature
• C. Nonce
• D. Pass-the-Hash

Answer: (B)

Digital signatures provide authenticity and non-repudiation using a public-key approach. In this scheme, the signer hashes the message and then encrypts that hash with their private key to create a signature. Anyone can verify the signature by decrypting it with the signer’s public key and comparing the result to a fresh hash of the received message. Because the private key is kept secret, only the legitimate signer could have produced the signature, proving who sent the message (authenticity) and preventing the signer from denying it later (non-repudiation). The other options don’t fit: a MAC uses a shared secret key and can’t prove which party signed a message to someone else; a nonce is just a value used to prevent replay attacks; pass-the-hash is a credential exploitation technique, not a method for providing authenticity and non-repudiation.