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I have been attempting to reverse engineer a format for a visual novel psp game ('Mirai Nikki RE: WRITE - 13 Ninme No Nikki Shoyuusha') and I have come to the understanding that the format works as a type of archive by looking at the boot.elf file of the game. From this decoded boot.elf file I learnt that music is stored in the format at3 (which is atrac3) and sound effects as fsb (fmod sound bank). There are multiple 'MIG' files which I believe are actually GIM files which is a format used by the PSP for images (these are likely the character portraits, backgrounds and ui). The string YKLZ is also repeated throughout the file and seems to act as a sort of file or directory end. The header T2FP also occurs.

After learning this I have hit a wall as I am unsure of how to progress in getting the files as I do not know how it is encrypted or where the files start and end. If anyone can tell me how I could go about reversing the decryption function in an emulator or can provide any help about the file it would be greatly appreciated.

Decrypted boot.elf

The game archive file

Edit: The hex code 87 4C 74 68 also occurs multiple times throughout the file.

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    Depending on the replies you receive here, I recommend inquiring on the XeNTaX and/or ZenHAX forums. Those two forums are dedicated to reversing file formats, especially in regards to video games. – dsasmblr Aug 11 '18 at 16:57
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    @dsasmblr Thanks for the suggestion, a post was made about the format before to zenhax but it didn't seem to get any good replies so if I don't get anything I'll try posting on both forums assuming it's not against the rules to create a thread that already existed. – StevenHughes Aug 11 '18 at 17:16
  • If that doesn't pan out for you, then you might want to delve into the PSP/Vita hacking scene and inquire. A good place to find people to inquire with might be the Henkaku Discord server: discord.gg/2bfq4XA There are primarily Vita hackers there, but they're a knowledgeable lot and should be able to point you in a good direction. – dsasmblr Aug 12 '18 at 3:31
  • @dsasmblr Thanks so much, I asked on XeNTaX but haven't got any answers yet so I'll wait an hour then try the discord. – StevenHughes Aug 12 '18 at 9:14

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