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(ExtdataID-High is always 00000000 for SD, and always 00048000 for NAND) Some titles can have Quota.dat stored in these directories. The directory-name for these directories is the ExtdataID-Low. Then there's a sub-directory 00000000, which contains the actual extdata. Size and number of files in this dir varies per title.
(ExtdataID-High is always 00000000 for SD, and always 00048000 for NAND) Some titles can have Quota.dat stored in these directories. The directory-name for these directories is the ExtdataID-Low. Then there's a sub-directory 00000000, which contains the actual extdata. Size and number of files in this dir varies per title.
NAND stores the shared extdata and is structured exactly the same way, see [[Flash Filesystem]].
NAND stores the shared extdata and is structured exactly the same way, see [[Flash Filesystem]].
Extdata image 00000001 contains a SAVE partition for the FST, the actual file data is stored in the following extdata images.
Regular apps can only mount SD extdata using the same extdataID which is stored in the [[NCCH#CXI|CXI]] exheader. Therefore, regular apps which have the exheader extdataID set to zero can't use extdata. This restriction doesn't apply for shared extdata with extdataID high bitmask 0x48000 stored on NAND. System apps with a certain access right can mount arbitrary extdata.
Regular apps can only mount SD extdata using the same extdataID which is stored in the [[NCCH#CXI|CXI]] exheader. Therefore, regular apps which have the exheader extdataID set to zero can't use extdata. This restriction doesn't apply for shared extdata with extdataID high bitmask 0x48000 stored on NAND. System apps with a certain access right can mount arbitrary extdata.
=== Encryption ===
=== Encryption ===
These files are [[AES|encrypted]] with AES-CTR, the keyslot is initialized by [[nand/private/movable.sed|movable.sed]]. The same keyslot is used for the NAND/SD extdata MAC, however NAND extdata is stored in cleartext. The WCHAR LowPath "/extdata/<ExtdataIDHigh>/<ExtdataIDLow>/<PathToImage>" text path is hashed with SHA-256, including the WCHAR null-terminator. A separate hash is used for Quota.dat. The base CTR seems to be then generated by XORing the calculated hash: CTRword[i] = Hashword[i] ^ Hashword[4+i].
These files are [[AES|encrypted]] with AES-CTR, the keyslot is initialized by [[nand/private/movable.sed|movable.sed]]. The same keyslot is used for the NAND/SD extdata MAC. The NAND extdata images which only contain the FST are stored in cleartext, while the file-data images are encrypted. The WCHAR LowPath "/extdata/<ExtdataIDHigh>/<ExtdataIDLow>/<PathToImage>" text path is hashed with SHA-256, including the WCHAR null-terminator. A separate hash is used for Quota.dat. The base CTR seems to be then generated by XORing the calculated hash: CTRword[i] = Hashword[i] ^ Hashword[4+i].
The base CTR is fixed therefore the CTR never changes after each write. Thus it is possible to obtain some cleartext by XORing one file(like newly created extdata) with a newer file, where the newer file overwrote zeros in the original file with non-zero data.
The base CTR is fixed therefore the CTR never changes after each write. Thus it is possible to obtain some cleartext by XORing one file(like newly created extdata) with a newer file, where the newer file overwrote zeros in the original file with non-zero data.
* /icon This file contains the extdata [[SMDH|icon]] displayed in data management. This icon can only be written to by titles when creating extdata, titles would have to recreate extdata to change the icon. This file can't be read directly, instead it is read via [[FS:ReadExtSaveDataIcon]].
* /icon This file contains the extdata [[SMDH|icon]] displayed in data management. This icon can only be written to by titles when creating extdata, titles would have to recreate extdata to change the icon. This file can't be read directly, instead it is read via [[FS:ReadExtSaveDataIcon]].
* /user/ Contains the title's actual extdata files.
* /user/ Contains the title's actual extdata files.
* /boss/ Can contain [[SpotPass]] content. SpotPass content is *always* stored in SD extdata.
* /boss/ Can contain [[SpotPass]] content. SpotPass content can only be downloaded to this /boss directory.
* /user/ExBanner This directory can optionally store [[Extended_Banner| extended banners]]. When this is available, this banner is displayed instead of the [[CXI]] ExeFS banner. COMMON.bin stores the common exbanner, while <regionlang_code>.bin stores an optional separate region/language specific banner.(regionlang_code can be "JPN_JP", "USA_EN", etc)
* /user/ExBanner This directory can optionally store [[Extended_Banner| extended banners]]. When this is available, this banner is displayed instead of the [[CXI]] ExeFS banner. COMMON.bin stores the common exbanner, while <regionlang_code>.bin stores an optional separate region/language specific banner.(regionlang_code can be "JPN_JP", "USA_EN", etc)