Power Consumption Calculation

[hanaabdelhakim]

Hello,

Are the traces resulting from the capturing considered power traces or voltage? I want to calculate the energy consumption. What I did was I treated the traces as voltage traces^2 divided it by 0.22(shunt resistance I assumed) then I got the area under the graph. Is that correct? I am using UFO Board and CWLITE Standalone.

Thanks

[jpthibault]

Unfortunately you can’t really do that:

What is the unit of power measured by Chipwhisperer Capture?

Hello, It doesn’t have a normal calibration (i.e., you can’t say off-hand what the exact amount is). You’d have to do a bit of a calibration to determine that, as it’s related to the power drop across the sense resistor. The input is AC-coupled too so it only measures changes in power consumption, not a direct DC offset. -Colin

[hanaabdelhakim]

Can you please explain more?

[hanaabdelhakim]

what calibration is required?

[jpthibault]

The calibration that one would do with say an oscilloscope.
In side-channel attacks we only really care about relative differences in measurements; we don’t care about absolute measurements. That’s why CW isn’t meant to be used that way.

[hanaabdelhakim]

what are differences in measurements relevant to? Like what is the first power trace that we measure the difference according to? Idle starting power=0 or power=rated?

[hanaabdelhakim]

Does that mean that the traces are voltage differences traces compared to the 3.3V? I am using STM32F3 on UFO board

[jpthibault]

Very roughly yes/maybe, but not really. Google “AC coupling vs DC coupling” to learn more. ChipWhisperer’s measurements are best considered dimensionless.
If you want to measure power/current/power properly, then there are tools for this purpose, for example https://www.joulescope.com/ (no affiliation).

[hanaabdelhakim]

OK I get you. Thanks for explaining.