Which method is used to authenticate a subject using an unpredictable value?

The challenge/response method is a widely recognized authentication mechanism that utilizes an unpredictable value, or a challenge, to verify the identity of a subject. In this process, the system generates a random challenge that the subject must respond to correctly using a predefined procedure. This response is typically generated by applying a cryptographic function to the challenge along with a secret key known only to the subject.

This method enhances security by ensuring that each authentication attempt requires a unique challenge, making it difficult for an attacker to reuse previous responses to gain unauthorized access. By requiring the subject to respond with a value that is derived from the challenge, the system effectively verifies both the identity of the user and their possession of the secret key.

The other choices do not employ an unpredictable value in the same way. Data Manipulation Language is primarily concerned with data operations in a database and doesn't relate to authentication. Callback techniques involve a two-step verification process but do not incorporate a unique challenge for every session. Compensating controls are alternative security measures put in place when the primary control fails but do not specifically describe an authentication method utilizing unpredictable values.