### Methodology of software expertise based on improved windowed entropy calculation algorithm

#### Abstract

The article discusses an algorithm for calculating the sliding entropy of a binary file with an intersection between adjacent blocks. The relevance of the study is due to the widespread use of entropy analysis in software expertise. The currently used algorithm for calculating entropy with intersection between adjacent blocks has quadratic complexity in the worst case. As a result, the entropy calculation algorithm used in the analysis tools divides the input file into disjoint blocks, which reduces the accuracy of entropy analysis. The paper analyzes the changes in the information entropy of a message when one character changes in it. It is determined that calculations of entropy changes, regardless of the ratio of the frequency of occurrence of deleted and added characters in the message, can be carried out in constant time. As a result of the analysis of the revealed dependencies, a more productive algorithm for calculating the sliding entropy of binary files with intersecting blocks has been developed. It is shown that the developed algorithm makes it possible to calculate entropy with an arbitrary amount of displacement between adjacent blocks of the file. An experimental evaluation of the accuracy and performance of the algorithm was carried out. It is revealed that the performance gain when using the developed algorithm increases with a decrease in the offset between adjacent blocks. The study is intended for specialists in the field of system analysis of software, as well as in the field of reverse engineering of software.

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