Model#

In order to protect something, you must first have a understand what that something is.

Start with a block diagram of how data flows through the system at the highest possible level.

block
    browser("Web browser") space server("Web server") space logic("Business Logic") space database("Database")
    browser<-->server
    server<-->logic
    logic<-->database

Add trust boundaries to show who controls what.

Note:

A trust boundary is formed at wherever people control different things. Some typical examples of trust boundaries include accounts, network interfaces, different physical computers, virtual machines, organisational boundaries, etc.

At this point, it is probably helpful to label data flows.

You should think of threat model diagrams as a part of the development process, so try to keep your diagram in version control with the rest of your project.

Tips:#

• Don’t have data sinks: You write the data for a reason. Show who uses it.
• Data can’t move itself from one data store to another: Show the process that moves it.
• Keep your diagram simple. For complicated parts of your system (e.g., diode structure), draw a separate diagram that focuses on just that block.