[Bug] DSi NAND mount mangles last 4 bytes of tickets

[Janni9009]

I was working on my manual DSi brick recovery guide again today, when I got stuck scratching my head on why twltool syscrypt was now failing.
Turns out, ninfs somehow mangles the last 4 bytes!

Left side is twltool nandcrypt + OSFMount, right side is NinFS. Same exact ticket. All other bytes match besides those last 4 at 0x2C0.

[ihaveamac]

I'm guessing pyctr is somehow failing to properly decrypt partial blocks (smaller than 16 bytes). TWL encryption is kinda weird and does some non-standard things.

[ihaveamac]

If you use ninfs to copy out the twlnand image file, it'd most likely decrypt fine there, since there would be no partial block decryption.