An Access-Control List (ACL) is a list of permissions that are associated with an object in a computer system. It specifies which users or system processes are granted access to the object and what operations are allowed to be performed on the object.
ACLs are used to enforce access control policies in a variety of systems, including file systems, databases, and operating systems. They are an important part of security and are used to protect against unauthorized access to resources.
There are two types of ACLs: discretionary and mandatory. A discretionary ACL (DACL) is a list of permissions that is associated with an object and specifies which users or system processes are granted access to the object. A mandatory ACL (MACL) is a list of permissions that is associated with an object and specifies which users or system processes are denied access to the object.
ACLs can be used to specify permissions at a very fine granularity. For example, in a file system, an ACL can be used to specify which users are allowed to read, write, execute, or delete a file. In a database, an ACL can be used to specify which users are allowed to read, write, or execute a particular database table or record.
To implement ACLs, a system must have a way to identify users and processes, a way to represent the permissions that are associated with an object, and a way to enforce the ACL when access to the object is requested. In some systems, ACLs are implemented using access-control lists, which are lists of users or groups and the permissions that are associated with them. In other systems, ACLs are implemented using access control matrices, which are tables that list the objects in the system and the permissions that are associated with each object for each user or group.
In summary, an Access-Control List is a list of permissions that is used to control access to resources in a computer system. It is an important part of security and is used to protect against unauthorized access to resources.