In public-key cryptography, which key verifies a signature?

• A. Sender's private key
• B. Public key certificate
• C. Session key
• D. Sender's public key

Answer: (D)

In public-key cryptography, a digital signature is created with the sender’s private key and verified with the corresponding public key. The verification process checks that the signature was produced using the private key tied to that public key, confirming the signer’s identity and that the message hasn’t been altered. A public-key certificate can be used to obtain or trust the public key, but the actual verification uses the public key itself. A session key is used for symmetric encryption and has no role in signature verification. The sender’s private key is for signing, not verifying, so the key that verifies a signature is the sender’s public key.