I’ve spent ages Googling, lurking in this forum, and even flipping through whitepapers, and electronics 101 articles looking for any guidance for my question with no luck.
I’m keen to try DPA on an external target, on the ground line. And I have so many questions - apologies and thanks in advance.
- How do I connect this all safely? I.e. The few instructions I’ve found related to VCC readings and I have no idea how much of that is even applicable to ground readings. Please help a noob out. What do I connect and where? My target is a little pcb with a soic8 chip, powered from a CR battery, with no serial inputs etc. I have little touch points on the board labelled: gnd, dat, clk, vcc.
1a. Do I need a “reference ground” from the target to the chipwhisperer/probe supply even though I’m measuring a ground signal for analysis?
1b. How do I avoid a ground loop here (sorry if this question is really silly, but I’d hate to blow something up and am risk averse)? I understand I need to connect probes to each side of the shunt, may or may not need a third wire to “reference ground” (can this be anywhere on the target that has 0v?), and need to connect something to trigger the chipwhisperer measurements and hook up the clock signal, but I don’t know how to identify safe places to do that. I have a chipwhisperer powered from my laptop (can unplug laptop from wall if this matters?), the official probe power supply connected to mains, and the target device is an external PCB powered by 2x 3v CR batteries. If more details are required please let me know what those are and I’ll post them.
1c. Does the advanced breakout board play into this? If so, how? If not, what is it supposed to be for?
- Ground shunts. Do I need to use something actually labelled a ground shunt, or can I use any resistor?
2a. How do I know what size resistor to use?
If there was an easy-for-noobs-to-follow diagram that included basic things like a line drawn from a gnd pad to the chipwhisperer to the pc to the wall (or not if you’re supposed to unplug it!) showing at their most basic and simple forms, how to wire everything up for VCC DPA, then another for GND, then another for power glitching, etc that would be extraordinarily helpful for newbies like me to conceptualize the way the connections should go.
Thanks for putting up with my questions. I enjoy the chipwhisperer so far, it’s a great concept and the build quality seems solid. When I read the description and the emphasis on making side channel attacks feasible and accessible for everyone I felt like it would give me a good learning foundation in terms of using it on real-world examples (external boards), but I feel like there is a huge gap here and I’m slowly trying to address it. It’s really hard to understand what you need to skill up on just to apply the same sorts of techniques to a truly external device. I’m sure I’ll get there eventually, and big thanks to everyone who takes the time to read and respond =)
Edit to add: I bought the power analysis / glitching level 2 starter pack. Probes etc I am trying to use are all a part of this pack. I also bought a soldering iron, heat gun, a multimeter, and a bunch of other stuff.
I’m good with software and security, but hardware is currently a bit like black magic to me.