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This page describes the format and encryption of extdata, "extra data" stored on [[SD_Filesystem|SD card]] and NAND.
This page describes the format and encryption of extdata, "extra data" stored on [[SD_Filesystem|SD card]] and NAND.
At /Nintendo 3DS/<SomeID>/<SomeID>/extdata/<ExtdataIDHigh> on SD is directories for each title.(ExtdataIDHigh seems to be always 00000000) Some titles have Quota.dat stored in these directories, not all titles use it. The dirname for these directories is the ExtdataIDLow. Then there's a sub-directory 00000000, which contains the actual extdata. Size and number of files in this dir varies per title.
At /Nintendo 3DS/<SomeID>/<SomeID>/extdata/<ExtdataIDHigh> on SD is directories for each title.(ExtdataIDHigh seems to be always 00000000) Some titles have Quota.dat stored in these directories, not all titles use it. The dirname for these directories is the ExtdataIDLow. Then there's a sub-directory 00000000, which contains the actual extdata. Size and number of files in this dir varies per title.
Regular apps can only mount SD/NAND extdata using the same extdataID which is stored in the [[CXI]] exheader. Therefore, regular apps which have the exheader extdataID set to zero can't use extdata. System apps can mount arbitrary extdata.
=== Encryption ===
=== Encryption ===
Most extdata uses the same FS as [[savegames]], except extdata uses [[Savegames|DIFF]] instead of DISA. However some extdata files are raw, without any FS.
Most extdata uses the same FS as [[savegames]], except extdata uses [[Savegames|DIFF]] instead of DISA. However some extdata files are raw, without any FS.
Quota.dat uses the same encryption as extdata, and seems to use the same FS as the actual extdata. Modifying various bytes in Quota.dat didn't cause any errors to be thrown, likewise for deleting Quota.dat on the latest system version. Titles that used to create Quota.dat on old sys versions, no longer create Quota.dat on the latest sys version. Therefore it's unknown whether Quota.dat is even used any-more on the latest system version at all.
Quota.dat uses the same encryption as extdata, and seems to use the same FS as the actual extdata. It's unknown whether Quota.dat is used anymore on the latest system version at all.
'''QUOT'''
'''QUOT'''