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→Encryption
=== Encryption ===
=== Encryption ===
The extended header, the [[ExeFS]], and the [[RomFS]] are encrypted using [https://github.com/3dshax/ctr/blob/master/ctrtool/ncch.c 128-bit AES CTR]. The decryption key is generated using the [[AES|AES Engine]] key generator, where the keyX is set by the bootrom (see below for the keyslots). Initially, the keyY was set to the first 0x10 bytes of the NCCH signature ("secure-crypto"). Later firmware updates introduced more sophisticated algorithms.
The extended header, the [[ExeFS]], and the [[RomFS]] are encrypted using [https://github.com/3dshax/ctr/blob/master/ctrtool/ncch.c 128-bit AES CTR] unless the NoCrypto mask is set in ncchflag[7]. The decryption key is generated using the [[AES|AES Engine]] key generator, where the keyX is set by the bootrom (see below for the keyslots). Initially, the keyY was set to the first 0x10 bytes of the NCCH signature ("secure-crypto"). Later firmware updates introduced more sophisticated algorithms.
Starting with [[9.6.0-24|9.6.0-X]] Process9, there is a different method of generating the NCCH keyY which is enabled by setting the bitmask 0x20 in ncchflag[7]: The keyY will be set to a SHA256 hash generated with the 0x20 bytes of data constituted by the old-method-keyY and a unique content lock seed (each of which are 0x10 bytes wide), where seeds for downloaded titles that use the new crypto are stored in [[Filesystem_services#SEEDDB|SEEDDB]] (nand:/data/<console-unique>/sysdata/0001000f/00000000). The decryption is transparent to ARM11 userland: When FSUSER OpenFile is used with a NCCH archive which uses this crypto, the FS-module will add the seed-data from SEEDDB to the end of the file lowpath used for [[FSPXI:OpenFile]], using which Process9 then gets the hash for calculating the NCCH keyY. It has been observed that this new keyY generation is only used for [[RomFS]] and for [[ExeFS]] sections other than "icon" and "banner" (the same sections which would be used for the additional NCCH keyslots, however this keyY generation can be used without any additional NCCH keyslot). Not applying the encryption to "icon" and "banner" was presumably done to support pre-loading of games from the eShop (i.e. being able to download and install titles without being able to start them until official release).
Starting with [[9.6.0-24|9.6.0-X]] Process9, there is a different method of generating the NCCH keyY which is enabled by setting the bitmask 0x20 in ncchflag[7]: The keyY will be set to a SHA256 hash generated with the 0x20 bytes of data constituted by the old-method-keyY and a unique content lock seed (each of which are 0x10 bytes wide), where seeds for downloaded titles that use the new crypto are stored in [[Filesystem_services#SEEDDB|SEEDDB]] (nand:/data/<console-unique>/sysdata/0001000f/00000000). The decryption is transparent to ARM11 userland: When FSUSER OpenFile is used with a NCCH archive which uses this crypto, the FS-module will add the seed-data from SEEDDB to the end of the file lowpath used for [[FSPXI:OpenFile]], using which Process9 then gets the hash for calculating the NCCH keyY. It has been observed that this new keyY generation is only used for [[RomFS]] and for [[ExeFS]] sections other than "icon" and "banner" (the same sections which would be used for the additional NCCH keyslots, however this keyY generation can be used without any additional NCCH keyslot). Not applying the encryption to "icon" and "banner" was presumably done to support pre-loading of games from the eShop (i.e. being able to download and install titles without being able to start them until official release).