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In computer security, general access control includes authorization, authentication, access approval, and audit. A more narrow definition of access control would cover only access approval, whereby the system makes a decision to grant or reject an access request from an already authenticated subject, based on what the subject is authorized to access. Authentication and access control are often combined into a single operation, so that access is approved based on successful authentication, or based on an anonymous access token. Authentication methods and tokens include passwords, biometric scans, physical keys, electronic keys and devices, hidden paths, social barriers, and monitoring by humans and automated systems. ==Software Entities== In any access-control model, the entities that can perform actions on the system are called ''subjects'', and the entities representing resources to which access may need to be controlled are called ''objects'' (see also Access Control Matrix). Subjects and objects should both be considered as software entities, rather than as human users: any human users can only have an effect on the system via the software entities that they control. Although some systems equate subjects with ''user IDs'', so that all processes started by a user by default have the same authority, this level of control is not fine-grained enough to satisfy the principle of least privilege, and arguably is responsible for the prevalence of malware in such systems (see computer insecurity). In some models, for example the object-capability model, any software entity can potentially act as both subject and object. , access-control models tend to fall into one of two classes: those based on capabilities and those based on access control lists (ACLs). * In a capability-based model, holding an unforgettable reference or ''capability'' to an object provides access to the object (roughly analogous to how possession of one's house key grants one access to one's house); access is conveyed to another party by transmitting such a capability over a secure channel * In an ACL-based model, a subject's access to an object depends on whether its identity appears on a list associated with the object (roughly analogous to how a bouncer at a private party would check an ID to see if a name appears on the guest list); access is conveyed by editing the list. (Different ACL systems have a variety of different conventions regarding who or what is responsible for editing the list and how it is edited.) Both capability-based and ACL-based models have mechanisms to allow access rights to be granted to all members of a ''group'' of subjects (often the group is itself modeled as a subject). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Computer access control」の詳細全文を読む スポンサード リンク
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