Which statement best describes a digital signature?

• A. To encrypt the entire message
• B. To sign a digital certificate for a website
• C. To authenticate a user to login
• D. To verify the authenticity and integrity of a message or document

Answer: (D)

A digital signature acts as a tamper-evident seal that proves who signed a piece of data and that its content hasn’t been altered. It uses asymmetric cryptography: the signer generates a signature with their private key on a hash of the message, and anyone can verify it with the signer’s public key. If the verification succeeds, you gain authenticity—the signer is who they claim to be—and integrity—the message is unchanged since it was signed. In many cases it also supports non-repudiation, meaning the signer can’t reasonably deny signing it if their private key was used.

Encrypting the entire message would provide confidentiality, not authenticity or integrity. Signing a digital certificate relates to certificate issuance and trust chains rather than the general purpose of a signature. Authenticating a user to log in is about access control, not signing data.