Trust Boundaries identify areas at a similar level of trust and isolate them from other areas at a different level of trust. For example, any flow from a Process toward an External Interactor must cross a Trust Boundary, because the first is at a much higher Trust level than the latter. The same applies to flows from Trust Boundaries to Processes.

Tips & Tricks
Avoid using Trust Boundaries when they are not necessary.
Analogously, if you have no Trust Boundary, you may have missed some. At the very least, you must ensure that all flows in or from External Interactors cross a Trust Boundary.

In Threats Manager Studio (TMS), Trust Boundaries can be created in the following ways:

• In diagrams, you can click the New Trust Boundary button from the Diagram ribbon.
• In diagrams, you can drag & drop the icon of the Trust Boundary from the Basic Objects stencil to the Drawing Pane.

• In the Drawing Pane, you can use the context menu, by clicking on an empty space with the right button of the mouse. You can then select the action Create a Trust Boundary.
• In the Home ribbon, open the Trust Boundary List and then click the Add Trust Boundary button.

The Trust Boundary List in the Home ribbon is also useful to get a comprehensive view of all the Trust Boundaries defined in the Threat Model.