Which encryption method does MS-CHAP use?

• A. Symmetric key encryption
• B. Public key encryption
• C. Both A and B
• D. Neither A nor B

Answer: (D)

MS-CHAP uses symmetric encryption in its authentication process. In the challenge-response flow, the server sends a random challenge and the client, using the user’s password, derives DES keys to encrypt that challenge and generate a response. The server can verify the response by performing the same operation with the known password hash. Since DES (a symmetric-key algorithm) is involved, this is not public-key (asymmetric) encryption. Therefore, describing MS-CHAP as using symmetric key encryption is correct, and labeling it as not using encryption or as using public-key encryption would be inaccurate.