In a digital signature, which element is used to verify the signer’s identity by decrypting with the signer’s private key and then verifying with the public key?

• A. Public key
• B. Hash of message encrypted with signer’s private key
• C. Symmetric key
• D. Timestamped hash with public key

Answer: (B)

In a digital signature, authenticity is established by creating a signature from the message that only the signer with the private key could produce. The element used to verify identity is the hash of the message that has been encrypted with the signer’s private key—the signature itself. During verification, you decrypt that signature with the signer’s public key to recover the hashed value, then independently hash the received message and compare the two hashes. If they match, it shows the signer who holds the private key corresponding to the public key approved the message.

So the signature is the encrypted hash of the message, which is why that option is the correct one. The public key alone doesn’t prove identity, a symmetric key isn’t used in this public-key signing process, and a timestamped hash with a public key isn’t the standard mechanism for verifying a signer’s identity.