![]() Print (" type ent for hes hes ent for les les") ![]() Taking an algo from here and modifying it a little import math While a low entropy blob will have a repeated sequence comprising only of a certain byte like 0x00 0r 0x55 or two bytes 0x0d0a ox222e etc or any series one less than 255 possible byte sequences That is the blob will be a repeated sequence comprising of all bytes between of 0x0.0xff Where all the 255 possible bytes will have equal frequenciesĠx10 or 0x80 or 0xff will all be seen 10 times in the same blob Simply put the highest compressed data will have the highest entropy While 'c' (1/16) has the least or a very minuscule probabilityĮntropy is a thermodynamic concept that was introduced to digital science (information theory)Īs a means to calculate how random a set of data is In the first string and its shuffled clones all have 4 chars with equal probability 4/16 or 1/4 or 25%īut in the second string char 'a' (8/16 ) or half of the data set has the highest probability Order here does not mean 'a' following 'a' kind of order it is to be interpreted as random / non random state of certain dataĪaaabbbbccccdddd or "abcdabcdabcdabcd" or "adbcadbcadbcadbc" is a repetitive string whose entropy will be greater thanĪaaaaaaabbbbcccd or any shuffled representation of this string You can also build your own tools that do this.Įntropy is interpreted as the Degree of Disorder or RandomnessĪ high entropy means a highly disordered set of dataĪ low entropy means an ordered set of data For example, we can usually differentiate between image files (png, jpeg, etc) and compiled binaries (ELF, PE) because image files consist of compressed data and therefore (generally) have much higher entropy than compiled binaries.īesides "Detect It Easy", tools such as binwalk, ent and binvis.io can assist with calculating file entropy. close to random), it makes no sense to try to treat it as code and disassemble it, because the results will be meaningless nonsense.įile Type Identification - Some file types can be identified on the basis of their overall entropy. If we have a block of data with very high entropy (i.e. To proceed with analysis of the actual firmware, it must first be decompressed/decrypted. If the entropy is very high, it is a good sign that the file is indeed compressed or encrypted. One way to determine this is through performing an entropy analysis of the file. In order to analyse the firmware, it first needs to be determined whether it is encrypted or compressed. If we want to analyze the code, its decompressed form need to be recovered somehow.įirmware Analysis - In systems with relatively severe hardware constraints, such as embedded systems, firmware updates are often delivered in compressed form in order to save space. Executable compression complicates analysis, so it is a relatively common feature of programs developed for criminal purposes. ![]() Malware Analysis - If we have an executable which has a header that can be parsed successfully and the program loads and runs without error, but the overall entropy level of the file is very high and the code can't be analyzed statically because the data outside of the file header and program headers looks random (hence the high entropy), it probably means that the executable is in fact compressed on disk and is decompressed at runtime. ![]() In fact, compressed and encrypted data have close to the maximum possible level of entropy, which can be used as a heuristic to identify it as such in order to differentiate it from non-compressed/non-encrypted data.Įxample use cases in reverse engineering: I want to know what it is used for?įor our purposes, entropy can be though of as information density or as a measure of randomness in information, which is what makes it useful in the context of reverse engineering and binary analysis.Ĭompressed and encrypted data have higher entropy than e.g.
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