Physical access to electronics generally means all bets are off when it comes to information security. But in special cases this is just unacceptable and a better solution must be found. Consider the encryption keys used by point of sale machines. To protect them, the devices incorporate anti-tamper mechanisms that will wipe the keys from memory if the device is opened. One such technique is to use a mesh of traces on a circuit board that are monitored for any changes in resistance or capacitance. [Sebastian Götte] has been researching in this area and wrote a KiCad plugin to automatically generate tamper-detection mesh.
The idea is pretty simple, place traces very close to one another and it makes it impossible to drill into the case of a device without upsetting the apple cart. There are other uses as well, such as embedding them in adhesives that destroy the traces when pried apart. For [Sebastian’s] experiments he’s sticking with PCBs because of the ease of manufacture. His plugin lays down a footprint that has four pads to begin and end two loops in the mesh. The plugin looks for an outline to fence in the area, then uses a space filling curve to generate the path. This proof of concept works, but it sounds like there are some quirks that can crash KiCad. Consider taking a look at the code if you have the expertise to help make it more stable.
We’ve seen these anti-tamper meshes in practice in the VeriFone payment terminal that [Tom Nardi] tore down a couple of years ago. The approach that [Sabastian] took with the plugin actually produces a more complex mesh than was in use there as it only really used vertical lines for the traces.