Security often concentrates at the door. One government report raises the question of what happens after someone gets past it.

The Perimeter Illusion

GAO investigators carrying the components for an improvised explosive device successfully passed undetected through security checkpoints. The report said the checkpoints were monitored by guards of the Federal Protective Service (FPS) at each of the 10 level IV federal facilities where GAO conducted covert testing. Wikipedia's current-events log for July 8, 2009, recorded that undercover investigators smuggled bomb-making materials into government buildings in the United States on ten occasions.

Once the GAO investigators passed the control access points, they assembled the explosive device. The report said they then walked freely around several floors of these level IV facilities.

Designing for Component Threats

One reading is that a checkpoint may be better at spotting a finished threat than its separate parts. In general, people screening a steady flow of visitors might find it hard to notice pieces that only matter once they are put together.

For people who design systems, this may illustrate a risk of relying only on the perimeter. If a perimeter can be breached by distributing a payload across multiple innocuous-looking packages, the interior environment requires its own continuous validation. A robust architecture might assume that components will eventually slip through the outer layer, shifting the focus from merely blocking entry to monitoring internal behavior and assembly.

Whether the setting is a building or a computer network, putting every check at the front door may leave the inside less protected. Perhaps resilience starts from asking what would happen if the door were already passed.

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