Which cryptographic method provides integrity and authenticity using a public-private key pair and a digital signature?

• A. Hash Function
• B. Digital Signature
• C. Nonce
• D. HTTPS

Answer: (B)

A digital signature uses a public-private key pair to give both integrity and authenticity to a message. The signer creates a hash (digest) of the message and then signs that digest with their private key. Anyone with the signer’s public key can verify the signature by hashing the received message and checking it against the signed digest. If the message has been altered, the digest won’t match, so verification fails, showing integrity. Because only the private key holder could have produced that signature, the verifier also gains authenticity and non-repudiation—the signer can’t deny having signed the data. Hash functions alone provide integrity without authentication, a nonce is for freshness, and HTTPS is about securing the transport layer rather than signing the data itself.