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This page describes the format and encryption of savegames stored in 3DS game cartridges/gamecards and SD/NAND. You can find savegames from various 3DS games on the [[Games]] page.

This page describes the format and encryption of savegames contained in gamecards, SD/NAND, and SD/NAND [[extdata]]. You can find savegames from various 3DS games on the [[Games]] page.

So how do you use this to decrypt a savegame on a 3DS? First off, you chunk up the savegame into 512 byte chunks. Then, you bin these chunks by their contents, discarding any that contain only FF. Now look for the most common chunk. This is your keystream. Now XOR the keystream with your original savegame and you should have a fully decrypted savegame. XOR with the keystream again to produce an encrypted savegame.

So how do you use this to decrypt a savegame on a 3DS? First off, you chunk up the savegame into 512 byte chunks. Then, you bin these chunks by their contents, discarding any that contain only FF. Now look for the most common chunk. This is your keystream. Now XOR the keystream with your original savegame and you should have a fully decrypted savegame. XOR with the keystream again to produce an encrypted savegame.

All savegames, including non-gamecard savegames, are encrypted with AES-CTR. The base CTR never changes after savegame creation. The CTR used for gamecard savegames eventually repeats, while non-gamecard savegames don't use a repeating CTR. For the old gamecard CTR method, it repeated every 0x200-bytes. With the new method it repeats at least every 0x1000-bytes, but the exact period isn't known for certain. Non-gamecard savegames use a separate CTR method from the gamecard savegames.

All savegames, including non-gamecard savegames, are encrypted with AES-CTR. The base CTR never changes after savegame creation. The CTR used for gamecard savegames eventually repeats, while non-gamecard savegames don't use a repeating CTR. For the old gamecard CTR method, it repeated every 0x200-bytes. With the new method it repeats at least every 0x1000-bytes, but the exact period isn't known for certain. Non-gamecard savegames use a separate CTR method from the gamecard savegames, see the [[extdata]] page regarding extdata encryption.

With system version [[2.0.0-4]] the system now uses a different CTR method, which fixed the above flaw. The CTR seems to repeat in the image but not every 0x200 bytes. The CTR may repeat every 0x1000 bytes. Every title since "Super Mario 3D Land" which have the [[NCSD|CCI]] NVer version set to the  [[2.0.0-4]] NVer version or higher uses this improved method, while older titles still use the old 0x200-byte period.

With system version [[2.0.0-4]] the system now uses a different gamecard CTR method, which fixed the above flaw. The CTR seems to repeat in the image but not every 0x200 bytes. The CTR may repeat every 0x1000 bytes. The system uses the new method for titles which have the [[NCSD|CCI]] NVer version set to the  [[2.0.0-4]] or above, starting with "Super Mario 3D Land". Prior to that NVer version, the system uses the old 0x200-byte CTR period.

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