Which of the following can be used as a keying method?

• A. Public key encryption for confidentiality
• B. MS-CHAP
• C. Both A and B
• D. None of the above

Answer: (A)

Keying methods describe how cryptographic keys are generated and used to protect data. Public key cryptography fits this role because it uses a public/private key pair to protect confidentiality: anyone can encrypt with the public key, but only the owner of the private key can decrypt, allowing secure communication without sharing secret keys in advance. MS-CHAP is an authentication protocol used to verify identity and may derive a session key for securing a session, but it is not a primary mechanism for providing data confidentiality through a keying method. Therefore, the public key approach is the appropriate keying method.