The program I'm trying to decompile uses several supporting files:

  • somesound.mp3
  • someimage.jpg
  • etc..

The files are all located in the file system, not embedded into the exe. The files are used at runtime for the game images and sounds.

If I try and open one of the mp3s or jpgs directly windows will give me an error, the files are obviously packed/encrypted/obfuscated/compressed.

How can I determine the obfuscation type of the files?

I have determined that the first 4 bytes are the same in each file, 43 46 31 30 (CF10 in ASCII). Maybe this information would be useful.

  • 1
    If those bytes are added to the original files, that's already enough to make them unusable with regular software. Check what's directly after them; does that data look like a JPEG, MP3, etc.? – Jongware Oct 15 '13 at 17:35
  • @Jongware No, there's no normal JPEG data after CF10. I found this question, it explains that CF10 means compression factor of 10 - stackoverflow.com/questions/113641/file-format-of-cf10-jpg – Drahcir Oct 15 '13 at 17:51
  • What OS you are using? – nrz Oct 15 '13 at 20:28
  • @nrz using windows 8 – Drahcir Oct 15 '13 at 21:18
  • 1
    Why don't you link a few example files or show us more than just the first four bytes. Somebody with a lot of experience with file formats might be able to spot the encoding. – Till Oct 16 '13 at 16:02

You can give a try to binwalk. This tool is able to do a wild guess about the encryption/compression routine used, with the -BE option.


(After finally being able to examine 2 examples)

They are regular files, obfuscated with a simple XOR encoding. See https://stackoverflow.com/questions/26442162/decryption-of-png-and-jpg-files for a longer description.

The file extension may or may not be the original one.

  • Wow, thanks for the response, looks good! I will test tomorrow and see if it works for my files as well. – Drahcir Oct 18 '14 at 18:48

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