Security Identifiers

Thus far we have been skirting the issue of identifiers. I mentioned earlier that a security principal is an entity that can have a security identifier (SID), but I never defined security identifier. Simply put, a SID is a (mostly) numeric representation of a security principal. The SID is actually what is used internally by the operating system. When you grant a user, a group, a service, or some other security principal permissions to an object, the operating system writes the SID and the permissions to the object's Access Control List (ACL).

SID Components

A SID is composed of several required elements. Figure 1-8 shows the different components of a SID.

Figure 1-8. A SID has a defined structure with several required elements. ...

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