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At /Nintendo 3DS/<SomeID>/<SomeID>/extdata/00000000 is directories for each title, with Quota.dat inside each dir. Quota.dat doesn't exist for all titles. 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/00000000 is directories for each title, with Quota.dat inside each dir. Quota.dat doesn't exist for all titles. Then there's a sub-directory 00000000, which contains the actual extdata. Size and number of files in this dir varies per title.
These files are encrypted with AES-CTR. The key is unknown, this is console-unique. The CTR includes the titleID and filename. The base CTR is fixed: 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. Most extdata uses the same FS as [[savegames]], except extdata uses DIFF instead of DISA. However some extdata files are raw, without any FS.
=== Encryption ===
These files are encrypted with AES-CTR. The key is unknown, this is console-unique. The CTR includes the titleID and filename. The base CTR is fixed: 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.
=== Filesystem ===
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 seems to use the same FS and encryption as the actual extdata?
'''QUOT'''
* This seems to be stored in the Quota.dat FS image somewhere?
{| class="wikitable"
|-
! Start
! Length
! Description
|-
| 0x0
| 4
| Magic ("QUOT")
|-
| 0x4
| 4
| Magic Number? (0x30000)
|-
| 0x8
| 8
| Unknown
|-
| 0x10
| 0x38
| Unknown
|}