In public-key encryption for authentication, the supplicant uses ________ to encrypt.

• A. The supplicant's private key
• B. The supplicant's public key
• C. The verifier's private key
• D. The verifier's public key

Answer: (A)

In authentication with public-key cryptography, the entity proving its identity creates a signature by using its private key to sign a challenge or message. The verifier then uses the corresponding public key to verify that signature. This proves that the signer possesses the private key without revealing it. Encrypting with the supplicant’s private key is the signing step, and it’s this action that authenticates the supplicant. Using the public key to encrypt would not support proving identity, and using the verifier’s keys would place the verifier at the center of the operation, which isn’t how the authentication process works.