How to Finagle a Decimation Testing Pass (N21c)
Decimation testing (in conjunction with IID testing) is the entropy estimation method which has been described by the CMUF Jitter Entropy Working Group and strongly recommended by CMVP for all Jitter/Jent and similar non-physical entropy source ESV submissions. Such testing aims to find a decimation level that results in the data passing the NIST IID tests, which are limited to a maximum 8-bit sample size. Often, the collected data fails to pass decimation testing at any level when using the basic mapping described in the Jent Heuristic document of using the 8 least significant bits from each sample. the speakers explore a particularly informative Jent data set which provides insight into which data properties are and are not capable of passing IID testing. Although this data set does not pass decimation testing when the 8 least significant bits are used, the speakers are able to use the results of the analysis to modify the mapping of the data down to fewer bits that will pass decimation/IID testing. the speakers also apply the results to other data sets, thereby converting data sets that failed decimation testing into data sets that pass decimation testing, and converting data sets that passed decimation testing with a large decimation level into data sets that pass decimation testing with a much lower decimation level.