All-NaN slice encountered

Embedded Security ChipWhisperer Software
1

Hi Colin,

Recently I have been getting this error warnings.warn(“All-NaN slice encountered”, RuntimeWarning).

I will capture the power traces using the multi victim board and use the data in the analyzer, before the end of the last week, It would just work and get the AES sub keys, now it just throws out this warning/error and returns a “nan” in the results table. Did something go wrong on the board while capturing?

chipwhisperer-0.10rc1\chipwhisperer-0.10rc1\software\chipwhisperer\analyzer\attacks\CPAProgressive.py:154: RuntimeWarning: invalid value encountered in divide
  diffs[key] = sumnum / np.sqrt(sumden)
C:\WinPython-32bit-2.7.6.4\python-2.7.6\lib\site-packages\numpy\lib\nanfunctions.py:319: RuntimeWarning: All-NaN slice encountered
  warnings.warn("All-NaN slice encountered", RuntimeWarning)
2

Hello,

What does the data traces look like? If you get that it suggests there is too little variance between traces, and some of the statistics are collapsing. Check the capture clock etc. is all working OK. Basically though I would inspect the traces visually, they should look similar to previous experiments.

Note you will also get that warning if the trace set is too small - i.e. if you run the analysis over 1-2 traces for example. In such case you can ignore the warning, as it’s only the first few data points which will fail. Further data points (which >5 traces are mixed in) should succeed. In your case it sounds like it’s saying that for the entire analysis, and not just the first few runs?