What is an access control list (ACL) and how is it used?

• A. A list of permissions attached to an object that defines which principals may access it and how.
• B. A protocol for encrypting data in transit.
• C. A type of firewall rule.
• D. A method for storing user credentials.

Answer: (A)

An access control list is a list of permissions attached to an object that defines which principals may access it and how. When a request to access the object is made, the system checks the ACL to see whether the requesting user or group is allowed to perform the desired action (such as read, write, or execute). If a matching entry grants that permission, access is allowed; if not, it’s denied. This setup lets you grant different rights to different users on the same resource, providing fine-grained control beyond simple owner-based permissions. ACLs are common on files and folders, but they also appear in databases, network devices, and cloud storage. They’re about controlling access, not about encrypting data, routing traffic, or storing credentials.