4 ms·

Could one defense be to design the chip to not have any empty space? In other words, fill in any empty area with test circuitry such that you couldn't tell whic

• impdmnt2Prgrss 10y ago
  It would be very complex to fill the entire chip with cells---whose functionality mattered, otherwise we the attacker could replace them without the defender noticing---and get them wired in to the rest of the chip. There is a tradeoff between area utilization and routability of the design: it gets exponentially more difficult to route a design as its area utilization increases. This is why most commercial chips have 20% to 30% of free space in the layout. Even worse, in many commercial chips, there are spare cells to allow for cheap low-level patching. The attacker can just swap out one of these cells with their own and have an attack that only modifies a single cell.