Who can verify a digital signature?

• A. Only the signer
• B. Anyone with the private key
• C. Anyone with the public key
• D. The Certificate Authority

Answer: (C)

A digital signature is verified with the public key. The signer uses their private key to create a signature on the message (often by signing a hash of the message). Anyone who has the corresponding public key can verify that signature by applying the verification algorithm and comparing it to a freshly computed hash of the message. If they match, it confirms that the signature was created with the matching private key and that the message hasn’t been altered, and this can be done by anyone who has the public key. The private key remains secret to the signer, which is what makes the signature trustworthy. The Certificate Authority’s role is to bind a public key to an identity, not to perform the verification itself.