In public key encryption for authentication, the verifier decrypts the ciphertext with the supplicant's public key.

• A. True
• B. False
• C. It depends on the algorithm
• D. Not enough information

Answer: (B)

Public-key authentication relies on proving possession of the private key that matches a known public key. The verifier uses the public key to check something that only the holder of the private key could produce, typically a digital signature. In practice, the supplicant signs a challenge or message with their private key, and the verifier uses the supplicant’s public key to verify the signature. If the signature checks out, the verifier is convinced the claimant possesses the private key without exposing it.

Decrypting with a public key isn’t how authentication works in this context. Decryption is performed with the corresponding private key, or a signature is verified with the public key. So the statement is false because the public key is not used to decrypt; it’s used to verify a signature (or to encrypt data intended for the private key holder).