In digital signatures, which key is used to verify the signature's authenticity?

• A. Public key.
• B. Private key.
• C. Symmetric key.
• D. Session key.

Answer: (A)

Digital signatures rely on asymmetric cryptography, where signing uses a private key and verification uses the corresponding public key. The signer applies their private key to generate a signature over the message, and anyone who has the paired public key can verify that signature to confirm who signed it and that the message hasn’t been tampered with. The public key is shared openly so verification can be done by others without exposing the secret private key. A symmetric key or a session key wouldn’t support this model, since they require sharing a secret for both signing and verification and don’t provide the same non-repudiation and broad verifiability. So, the key used to verify the signature’s authenticity is the public key.