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Authorization (also spelt Authorisation) is the function of specifying access rights to resources, which is related to information security and computer security in general and to access control in particular. More formally, "to authorize" is to define access policy. For example, human resources staff are normally authorized to access employee records, and this policy is usually formalized as access control rules in a computer system. During operation, the system uses the access control rules to decide whether access requests from (authenticated) consumers shall be granted or rejected. Resources include individual files' or items' data, computer programs, computer devices and functionality provided by computer applications. Examples of consumers are computer users, computer programs and other devices on the computer.



Access control in computer systems and networks relies on access policies. The access control process can be divided into two phases: 1) policy definition phase, and 2) policy enforcement phase. Authorization is the function of the policy definition phase which precedes the policy enforcement phase where access requests are granted or rejected based on the previously defined authorizations.

Most modern, multi-user operating systems include access control and thereby rely on authorization. Access control also makes use of authentication to verify the identity of consumers. When a consumer tries to access a resource, the access control process checks that the consumer has been authorized to use that resource. Authorization is the responsibility of an authority, such as a department manager, within the application domain, but is often delegated to a custodian such as a system administrator. Authorizations are expressed as access policies in some type of "policy definition application", e.g. in the form of an access control list or a capability, on the basis of the "principle of least privilege": consumers should only be authorized to access whatever they need to do their jobs. Older and single user operating systems often had weak or non-existent authentication and access control systems.

"Anonymous consumers" or "guests", are consumers that have not been required to authenticate. They often have limited authorization. On a distributed system, it is often desirable to grant access without requiring a unique identity. Familiar examples of access tokens include keys and tickets: they grant access without proving identity.

Trusted consumers that have been authenticated are often authorized to unrestricted access to resources. "Partially trusted" and guests will often have restricted authorization in order to protect resources against improper access and usage. The access policy in some operating systems, by default, grant all consumers full access to all resources. Others do the opposite, insisting that the administrator explicitly authorizes a consumer to use each resource.

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