What is the name of the authentication system that generates secret key encrypted one-time passwords using a counter?

• A. Counter-Based Authentication System
• B. Time-based One-Time Password
• C. Challenge-Response
• D. Kerberos

Answer: (A)

This is about one-time passwords generated from a shared secret using a moving factor, specifically a counter. In this approach, both the client and server know a secret key, and a counter value increments with each code. The OTP is produced by applying a cryptographic function (like HMAC) to the secret key and the current counter, yielding a unique code for that counter. This means the password is valid only for that particular counter step.

Time-based variants use the current time as the moving factor, not a counter, so they would be described as time-based rather than counter-based. Challenge-response involves a separate challenge from the server rather than a counter-derived OTP, and Kerberos uses tickets in a centralized authentication framework.

Therefore, the option that describes a counter-based approach best matches this mechanism.