21. Security Identifier (SID)

• A SID is a unique name (an alphanumeric character string) that identifies each

  • operating system,

  • user,

  • user group, and

  • object in a network

  of Windows NT/2000/XP/2003 systems.

• Windows grants or denies access and privileges to resources based on access control lists (ACLs).

• When a user requests access to a resource, the user's SID is checked by the ACL to determine if that user is allowed to

  1. perform that action, or

  2. if that user is part of a group that is allowed to perform that action.