This is a neat paper. One of the tricky parts of making a malicious circuit is the fact that you want your behavior to only be triggered on some unlikely condit

This is a neat paper. One of the tricky parts of making a malicious circuit is the fact that you want your behavior to only be triggered on some unlikely condition. In other words you want: if (counter == 0x686e686e) { do evil } else counter++; But that requires a lot of hardware. What the authors realized is that essentially a simple capacitor can be used as a counter! Each time you reach the condition it adds a bit of charge to the capacitor, until at the appropriate moment it discharges and changes the state of the chip in some way. This is a really clever bit of design, getting something general-purpose and malicious out of a single capacitor!