Which statement correctly differentiates a digital signature from a hash?

• A. A digital signature binds the private key to the message, providing authenticity and nonrepudiation; a hash alone only provides integrity
• B. A hash provides nonrepudiation
• C. A digital signature provides confidentiality
• D. A hash proves origin

Answer: (A)

A digital signature binds the signer’s private key to the message, so others can verify who signed it and cannot later deny having done so. In practice, the signer creates a cryptographic hash of the message and then encrypts that hash with their private key. Anyone with the signer’s public key can decrypt the signature and compare the result to the hash they compute from the message themselves. If they match, it proves authenticity (the signer is who they claim) and nonrepudiation (the signer cannot plausibly deny signing).

A hash, by itself, only provides integrity. It is a fixed-size digest of the data, and while it can show if the message has been altered, it does not involve a private key or any mechanism to prove who created it. Without the signing step, a hash does not establish authenticity or nonrepudiation.

The other options don’t fit because a hash does not provide nonrepudiation, a digital signature does not inherently provide confidentiality (that would be encryption), and a hash does not prove origin.