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→Data Structure: don't repeatedly mention that files are encrypted, if it's only the SD layer encryption
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"'''<ContentID>.tmd'''" - (The Content ID is a u32, initially: '''00000000''' when the title is first installed. Changing by an increment of +'''0x1''' for each title update the 3DS installs) This is the [[Title metadata]] associated with the title, it is encrypted with a console-unique [[AES|keyslot]]. The decrypted TMD is available on Nintendo's CDN server at "http://nus.cdn.c.shop.nintendowifi.net/ccs/download/TitleIDhere/tmd.OptionallyTitleVersionHere". Though CDN version of the title TMD has a certificate chain attached at the end of the TMD, so removing it will give you the 1:1 decrypted TMD. After installation the "<ContentID>.tmd" is redundant, because important title data is extracted and imported into the [[Title Database|title.db]] and ".cmd" files, but is however kept as a reference.
"'''<ContentID>.tmd'''" - (The Content ID is a u32, initially: '''00000000''' when the title is first installed. Changing by an increment of +'''0x1''' for each title update the 3DS installs) This is the [[Title metadata]] associated with the title. The decrypted TMD is available on Nintendo's CDN server at "http://nus.cdn.c.shop.nintendowifi.net/ccs/download/TitleIDhere/tmd.OptionallyTitleVersionHere". Though CDN version of the title TMD has a certificate chain attached at the end of the TMD, so removing it will give you the 1:1 decrypted TMD. After installation the "<ContentID>.tmd" is redundant, because important title data is extracted and imported into the [[Title Database|title.db]] and ".cmd" files, but is however kept as a reference.
"'''<ContentID>.app'''" - (The Content ID is a u32, taken from the title's [[TMD]]) These files are [[NCCH]] files, where the entire file is encrypted with a console-unique [[AES|keyslot]](this is on top of the encryption of the NCCH contents). There can be more than one NCCH in this directory, as seen with .[[CCI]] files, the game executable ([[CXI]]) can be accompanied with additional non-executable NCCH files ([[NCCH#CFA|CFA]]) such as the electronic manual and DLP Child containers. Determining the function of the encrypted NCCH, is done by finding the Content Index of the "XXXXXXXX.app" file in the title's TMD(see above for retrieving decrypted TMD), interpreting the Content Index is as follows (does not apply to DLC content):
"'''<ContentID>.app'''" - (The Content ID is a u32, taken from the title's [[TMD]]) These files are [[NCCH]] files. There can be more than one NCCH in this directory, as seen with .[[CCI]] files, the game executable ([[CXI]]) can be accompanied with additional non-executable NCCH files ([[NCCH#CFA|CFA]]) such as the electronic manual and DLP Child containers. Determining the function of the NCCH, is done by finding the Content Index of the "XXXXXXXX.app" file in the title's TMD(see above for retrieving decrypted TMD), interpreting the Content Index is as follows (does not apply to DLC content):
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"'''<ContentID>.cmd'''" - (The Content ID is a u32, initially: '''00000001''' when the title is first installed. Changing by an increment of +'''0x1''' for each time the 3DS adds/removes '.app' files) This file contains data taken from the title's [[TMD]]. See the below table for the format of the cleartext .cmd file. The [[Title Database|Title.db]] contains the Content ID for the '.cmd' file, but does not contain a hash of the '.cmd' file. In addition it is also encrypted with a console-unique [[AES|keyslot]]. This acts as part of the DRM for installed titles, along with the [[Title Database|title.db]].
"'''<ContentID>.cmd'''" - (The Content ID is a u32, initially: '''00000001''' when the title is first installed. Changing by an increment of +'''0x1''' for each time the 3DS adds/removes '.app' files) This file contains data taken from the title's [[TMD]]. See the below table for the format of the cleartext .cmd file. The [[Title Database|Title.db]] contains the Content ID for the '.cmd' file, but does not contain a hash of the '.cmd' file. This acts as part of the DRM for installed titles, along with the [[Title Database|title.db]].
The below AES-CMACs(including the last 0x10-bytes of the header) are only used for SD titles, for NAND [[Title_list|download-play]] titles, and non-system DSiWare titles. For other titles, these MACs are set to all-zero.
The below AES-CMACs(including the last 0x10-bytes of the header) are only used for SD titles, for NAND [[Title_list|download-play]] titles, and non-system DSiWare titles. For other titles, these MACs are set to all-zero.
'''"00000001.sav"''' - This is the title's encrypted [[Savegames|savegame]]. Renaming these savegames causes home-menu to hang while launching titles, modifying these saves results in the same corruption errors as other savegames.
'''"00000001.sav"''' - This is the title's [[Savegames|savegame]]. Renaming these savegames causes home-menu to hang while launching titles, modifying these saves results in the same corruption errors as other savegames.
'''"00000000.ctx"''' - This file encrypted with a console-unique [[AES|keyslot]] is temporarily stored on SD card while a title is being downloaded from the eShop, it is deleted after the download is completed. This contains an AP0000000000000000 cert used to sign the data following the cert, this cert is signed by the [[CTCert]].
'''"00000000.ctx"''' - This file is temporarily stored on SD card while a title is being downloaded from the eShop, it is deleted after the download is completed. This contains an AP0000000000000000 cert used to sign the data following the cert, this cert is signed by the [[CTCert]].
The unknown signed data is likely an ECDSA public key. There's .ctx files stored under the /title directory for NAND CTR/TWL titles, however those use the [[CTXT]] format which is completely different from this SD .ctx format. These .ctx files for NAND/SD titles only exist for titles where installation was not yet finalized(like when a system update install was not yet finalized).
The unknown signed data is likely an ECDSA public key. There's .ctx files stored under the /title directory for NAND CTR/TWL titles, however those use the [[CTXT]] format which is completely different from this SD .ctx format. These .ctx files for NAND/SD titles only exist for titles where installation was not yet finalized(like when a system update install was not yet finalized).