I'm trying to unpack an obb file used in an android game. From my initial google searches, it's my understanding that an obb can be basically any type of file. The only lead I have is the magic bytes at the start of the file spell out "AP_Pack!", but I couldn't find any format matching it.

This is where I'm currently stumped so any next steps would be greatly appreciated.


Decompile the app and look for references to the magic signature. Unless it is obfuscated, it should not be too difficult to recover the format details from the code.

P.S. this project seems to have an unpacker referencing the magic string.

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  • Thanks! I was able to figure it out from the project you linked. – Andrew Jones Aug 17 '18 at 19:27

Have you tried to open the file with a HEX editor - for example - 010 Editor (https://www.sweetscape.com/010editor/) ? You can then see the first bytes of the file and look them up here: https://en.wikipedia.org/wiki/List_of_file_signatures

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  • Sorry, I think I used some of the wrong terms. When I said the magic bytes are "AP_Pack!", I meant that I had opened the file in a hex and looked at the first bytes and that's what they were. I had checked a couple of list of file signatures, but I couldn't find any that matched. If it's any help the hex version of the first bytes is 41:50:5f:50:61:63:6b:21. – Andrew Jones Aug 16 '18 at 12:18

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