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I want to analyze an executable that went through a packer to look for the parts that have been compressed or encrypted. Of course, it also means that I want to find the code for the decompression or decryption procedures in the executable. How can I find these ?

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    Generically for all executables packed with any packer? Or generically for all executables packed with a specific packer? Or specifically for a single executable packed with a specific packer? – Jason Geffner May 20 '15 at 19:33
  • Generally for all packer and all executable.If packer Specified, this work is easy – Alireza Jafari Fard May 21 '15 at 13:41
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A good way to find compressed or encrypted parts in a binary is entropy investigation, as compressed and encrypted parts show a high degree of disorder (a value of 1 means maximum disorder). I can recommend the tool binwalk which produces a graphical output of the memory's entropy. The picture shows a binwalk output, as an example of such a static analysis of an embedded device, showing typical entropies of different memory parts. enter image description here

The bottom part is an overlay of the corresponding Ida memory map.

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For most packers out there:

  • The start of the decompression or decryption is pretty much the entry point (with a bit of anti-debugging mixed in, perhaps).
  • The end of the decompression or decryption can't be found generically with static analysis.

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