Using a Balun for Current-Based Side Channel Attacks #ReverseEngineering

Limpkin’s blog describes looking to reverse engineer electronics using a component not often thought of: a balun.

I … came up with the above concept which uses a balun to provide isolated current measurements: the balun primary/left side is isolated from its secondary/right side!

This effectively means that you can place this device on the Device Under Test (DUT) “high side” (on its power supply rail) or on its “low side” (between the DUT and its ground) as the amplification output ground is floating. On top of that, having an isolated output prevents ground loops, which could have introduced noise at our input!

The only downside of baluns is that they don’t handle DC well, which is actually perfectly fine for me as side channels attacks only care about frequencies above 2MHz.
In the above diagram, DC current will go through the shunt resistor while the AC current will go through both the shunt and the balun.

The board at the top of this post is the resulting circuit with amplification.

See the entire process in the post here.


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