Applying the principle of least privilege is the best approach for controlling access to highly sensitive information when employees have the same level of security clearance. The principle of least privilege is a security concept that states that every user or process should have the minimum amount of access rights and permissions that are necessary to perform their tasks or functions, and nothing more. The principle of least privilege can provide several benefits, such as:

Improving the security and confidentiality of the information by limiting the access and exposure of the sensitive data to the authorized users and purposes

Reducing the risk and impact of unauthorized access or disclosure of the information by minimizing the attack surface and the potential damage

Increasing the accountability and auditability of the information by tracking and logging the access and usage of the sensitive data

Enhancing the performance and efficiency of the system by reducing the complexity and overhead of the access control mechanisms

Applying the principle of least privilege is the best approach for controlling access to highly sensitive information when employees have the same level of security clearance, because it can ensure that the employees can only access the information that is relevant and necessary for their tasks or functions, and that they cannot access or manipulate the information that is beyond their scope or authority. For example, if the highly sensitive information is related to a specific project or department, then only the employees who are involved in that project or department should have access to that information, and not the employees who have the same level of security clearance but are not involved in that project or department.

The other options are not the best approaches for controlling access to highly sensitive information when employees have the same level of security clearance, but rather approaches that have other purposes or effects. Audit logs are records that capture and store the information about the events and activities that occur within a system or a network, such as the access and usage of the sensitive data. Audit logs can provide a reactive and detective layer of security by enabling the monitoring and analysis of the system or network behavior, and facilitating the investigation and response of the incidents. However, audit logs cannot prevent or reduce the access or disclosure of the sensitive information, but rather provide evidence or clues after the fact. Role-Based Access Control (RBAC) is a method that enforces the access rights and permissions of the users based on their roles or functions within the organization, rather than their identities or attributes. RBAC can provide a granular and dynamic layer of security by defining and assigning the roles and permissions according to the organizational structure and policies. However, RBAC cannot control the access to highly sensitive information when employees have the same level of security clearance and the same role or function within the organization, but rather rely on other criteria or mechanisms. Two-factor authentication is a technique that verifies the identity of the users by requiring them to provide two pieces of evidence or factors, such as something they know (e.g., password, PIN), something they have (e.g., token, smart card), or something they are (e.g., fingerprint, face). Two-factor authentication can provide a strong and preventive layer of security by preventing unauthorized access to the system or network by the users who do not have both factors. However, two-factor authentication cannot control the access to highly sensitive information when employees have the same level of security clearance and the same two factors, but rather rely on other criteria or mechanisms.