Xbox 360 digital title preservation

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Qubits
Posts: 3
Joined: 06 Aug 2021 10:28

Re: Xbox 360 digital title preservation

Post by Qubits »

Resistiv wrote: 22 Jan 2020 02:07 Yes, it looks like you can indeed just copy over files from a hard drive using something like FATXplorer, however the files are often signed differently in their headers, which produces differing hashes. Here's looking at one dump, comparing my dump (left) and the scene dump in the dat (right) of N+ (World) (XBLA). Everything after the highlighted byte is matching in the attached image. Of course, more samples will be needed for decisive action, but it seems that the first 568 bytes (0x238) can be skipped when hashing.
I can explain this in general. Your dump is a PIRS type STFS file, which is a dump from a disc. The other is a LIVE type STFS which is a downloaded dump from XBOX live. The signatures at the beginning are different because the key for the digital signature of PIRS and LIVE files differ.
Hiccup
Datter
Posts: 1162
Joined: 09 Oct 2015 11:29

Re: Xbox 360 digital title preservation

Post by Hiccup »

Nice work. It sounds like that this signature should be kept (maybe even if its contains console specific info) as it can br used to verify contents, but it should be split from the file so that consistent hashes for the main file can be achieved, and so that these stripped third party dumps can be included in the dat.
Qubits
Posts: 3
Joined: 06 Aug 2021 10:28

Re: Xbox 360 digital title preservation

Post by Qubits »

The signature does not contain console info.
The signature is generated from 280 bytes of a certain area in the header.
These 280 bytes include console specific info as well as the "top" hash of all files (bit difficult to explain, hashes are generated for blocks, then like a pyramid there are hashes of hashes created, resulting in a "top" hash).

It's difficult to strip something. the STFS files are what really is transfered from xbox live.
(not for example like nsps, where the ncas is what's actually downloaded).
So stripping something would mean creating more or less your own file format. If you cut the header, the file would become unusable on original hardware.

There's nothing like what you call a "main file". STFS is a container format (like e.g. ncas are too).
So you could extract that container. These often contain 100s or 1000s of files. You *could* dat those, but again extracted files are not usable.

Datting XBLA and XBLIG games is unproblematic. As written, trials always exist so everyone downloading the trial of the game gets the exact same file and when using dashlaunch it's the full game.
Datting and preserving these also makes sense because they are fully funktional as trials on unmodified hardware.

The question is how to dat the DLCs. I think the best option, considering everything, would be to go with your initial idea and zero out parts of the header that are unique.
Hiccup
Datter
Posts: 1162
Joined: 09 Oct 2015 11:29

Re: Xbox 360 digital title preservation

Post by Hiccup »

Well I was just referring to the DLC when I mentioned console-unique data in the last post. Yeah I guess that third party dumps with removed signature could just be marked as such, and marked as bad. For DLCs, as well as zeroing out the unique data, maybe it could be stored in a seperate ("made-up") file (as long as the dumper in question is okay with that).
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