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游戏存档

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本页面描述了 3DS游戏卡, SD/NAND,SD/NAND extdata 中以及别的地方发现的游戏存档格式，加密方法等等内容。你可以在游戏页面找到多种游戏的存档。

加密手段

3DS上的游戏存档与DS的很像，都储存在游戏卡带的一块闪存芯片(FLASH chip)上。DS上这些游戏存档以明文的方式保存，3DS加了一层加密。通过对一些游戏存档的内容进行异或操作,显示出一些明文,看起来存档的加密方式应该是AES-CTR.

这样猜测的理由在于序列密码法曾有一段时间使用512字节（作为单位来加密），即是说，在超过512字节之后，这种加密方法将重复某些关键字序列(keystream)。序列密码法加密的方法是，使用关键字序列对待加密数据进行异或操作，（得到的便是加密数据）。不幸的是，假如你使用重复的关键字序列加密某些已知的明文（在我们的场合里，是数据0），那么你基本上在泄漏你宝贵的关键字序列。（译者注:在位(Bit)级别上进行异或运算时，1^0=1,0^0=0，这里符号"^"表示异或，所以一个数据和0进行异或时会得到它本身。）

那么怎么在3DS上运用这种解密方法呢？首先，将游戏存档切成以512字节为单位长度的片段，然后将除了只包含FF以外的片段以二进制方式查看。现在寻找最常见的公共片段，那就是你的关键字序列。现在用你原始的游戏存档和这些关键字序列进行异或操作，你将得到一个完全解密的游戏存档。对关键字序列进行异或操作以产生加密的游戏存档。（译者注:异或运算的一个重要性质是,a^b^b=a;即使用同样的关键字b对a进行两次异或将得到a本身，所以使用关键字序列对加密的游戏存档异或会得到明文，再异或一次又得到加密的存档。）

所有的游戏卡和SD卡存储的游戏都是用AES-CTR加密的. The gamecard savegame keyslot keyY is unique for every region of each game. A flag stored in the NCSD determines the method used to generate this keyY. This same flag is also used for determining which CTR method is used as well. The keyY when the flag is clear is generated from data stored in the main CXI, and data retrieved from gamecard commands. When the flag is set, a hash is generated for the keyY over the data from the CXI, and an ID retrieved from a gamecard command. The base CTR for gamecard savegames is all-zero. SD savegames use a CTR where the base CTR is fixed per savegame, however the CTR doesn't repeat in the image.

2.0.0-4(以及之后)的系统中,可以使用不同的游戏卡CTR方式，修正了上述缺陷。在 2.2.0-4 中,系统检查NCSD标志.如果被置位,使用新的CRT方式,否则就使用0x200-byte CRT.发布 2.2.0-4之后的所有游戏NCSD都被置位了,CRT不再在image中重复.


使用新加密方式的游戏:

  • Super Mario 3D Land 《超级马里奥3D大陆》
  • Mario Kart 7 《马里奥赛车7》
  • Need for Speed - The Run 《极品飞车-亡命狂飙》

一些信息:

  • 旧游戏仍使用0x200字节的异或加密方式。
  • 新游戏存档可以被备份和再储存（同样的密钥将被一个个存档使用）。New games saves can be backed-up and restored (same key is used from one save to another).
  • （wearleveling） 没有变化。
  • 对两个文件使用异或将产生一些明文。
  • 0x1000字节后，异或操作将停止。（所以 0x1000 可能是最大长度，但还未证实）

Wear leveling

3DS在游戏存档闪存芯片上引入了wear leveling 方案。这是通过使用blockmap和journal来实现的。blockmap在闪存上偏移量为0，其后是journal。初始状态由blockmap指定，然后journal对其进行应用。

The 3DS employs a wear leveling scheme on the savegame FLASH chips. This is done through the usage of blockmaps and a journal. The blockmap is located at offset 0 of the flash chip, and is immediately followed by the journal. The initial state is dictated by the blockmap, and the journal is then applied to that.

首先，是8字节目前还不明白其确切意义的数据。然后是实际的blockmap。其结构很简单： 

struct header_entry {
        uint8_t phys_sec; // when bit7 is set, block has checksums, otherwise checksums are all zero
        uint8_t alloc_cnt;
        uint8_t chksums[8];
} __attribute__((__packed__));

每个sector有一个入口，从实际的sector1开始计数（sector 0 包含blockmap/journal）。

blockmap后2字节为最开始的8个字节，以及blockmap的CRC16校验码（开始值为0xFFFF（像modbus））。 The 2 bytes that follow the blockmap are the CRC16 (with starting value 0xFFFF (like modbus)) of the first 8 bytes and the blockmap.

然后是journal。其结构如下: 

struct sector_entry {
        uint8_t virt_sec;       // Mapped to sector
        uint8_t prev_virt_sec;  // Physical sector previously mapped to
        uint8_t phys_sec;       // Mapped from sector
        uint8_t prev_phys_sec;  // Virtual sector previously mapped to
        uint8_t phys_realloc_cnt;       // Amount of times physical sector has been remapped
        uint8_t virt_realloc_cnt;       // Amount of times virtual sector has been remapped
        uint8_t chksums[8];
} __attribute__((__packed__));

struct long_sector_entry{
        struct sector_entry sector;
        struct sector_entry dupe;
        uint32_t magic;
}__attribute__((__packed__));

With magic being a constant 0x080d6ce0.

The checksums in the blockmap/journal entries work as follows:

  • each byte is the checksum of an encrypted 0x200 bytes large block
  • to calculate the checksum, a CRC16 of the block (with starting value 0xFFFF) is calculated, and the two bytes of the CRC16 are XORed together to produce the 8bit checksum

Partitions

There can be multiple partitions on the chip. The partitions are represented by tables of DIFI blobs inside a DISA structure. The order of the DIFI blobs is the order of the partitions in the chip.

DISA

  • If the uint32 @ 0x168 into the image in the DISA(the low 8-bits) is non-zero, then first table is is hashed, otherwise the second DIFI table is hashed.
  • If the table has more then 1 DIFI then the uint32 @ 0x168 is the offset from the DATA partition to the file base (masked with 0xFFFFFFFE).
  • At offset 0x0 in the image is a 0x10-byte MAC over the 0x100-byte DISA/DIFF, it might be AES-CCM MAC but it's unknown for certain. The following 0xf0-bytes after the MAC normally must be zero, it's unknown whether this can ever be non-zero.
Start Length Description
0x00 4 Magic ("DISA")
0x04 4 Magic Number (0x40000)
0x08 8 Partition table size
0x10 8 Offset to primary partition table in DISA
0x18 8 Offset to secondary partition table in DISA
0x20 8 Partition table's length
0x28 8 SAVE Partition entry offset in the partition table
0x30 8 SAVE Partition entry length in the partition table
0x38 8 DATA Partition entry offset in the partition table
0x40 8 DATA Partition entry length in the partition table
0x48 8 SAVE Partition offset
0x50 8 SAVE Partition length
0x58 8 DATA Partition offset
0x60 8 DATA Partition length
0x68 4 Active table (and the offset to the filebase)
0x6C 0x20 Hash from active table
0x8C 4*29 Unknown
  • The hash in the DISA hashes the Active Table (starting from tables's offset to tables's offset + table length) with SHA256.
  • The partitions offsets points to a 0x1000 long block which isn't understood yet. The actual information starts after that block.

The DIFIs table @ 0x200 (into the image) is written twice, (Meaning, if there's 4 DIFI blobs then the table is 2 DIFIs long).

The second table is for backup. The active table is mentioned at 0x13C into the image (1=First table, other=Second Table)

DIFF

  • This is the extdata equivalent of DISA, for extdata which use FS. DIFF is *only* used with extdata, not regular savegames.
  • When the active-table field low 8-bits is non-zero, the primary partition is used. Otherwise, the secondary partition is used.
Start Length Description
0x00 4 Magic ("DIFF")
0x04 4 Magic Number (0x30000)
0x08 8 Primary partition table offset
0x10 8 Secondary partition table offset
0x18 8 Partition table length
0x20 4 Active table (and the offset to the filebase)
0x24 0x20 Unknown
0x34 0x20 Hash of the active partition table
0x54 0x1ac Unknown

DIFI

These 0x130 large blobs describe the partitions. Every DIFI blob describes a partition. Partitions are catted together, so after the end of one partition is the beginning of the next.

Actually DIFI blobs are 0x12C large because the last 4 are not used and appear 0xFFFFFFFF at the encrypted image.

For most games there's only 1 partition (The SAVE partition) and some (like Asphalt 3D, Steel Diver & Lego Star Wars III) has 2 partitions.

  • 2 Partitions means that the files inside the SAVE partition is on the other partition (we would call it DATA partition).
  • No more than 2 partitions have been seen yet (and can't be because of the DISA known structure).
Start Length Description
0x00 4 Magic ("DIFI")
0x04 4 Magic Number (0x10000)
0x08 8 Offset to "IVFC" blob in DIFI (usually 0x44)
0x10 8 Size of "IVFC" blob
0x18 8 Offset to "DPFS" blob in DIFI (usually 0xBC)
0x20 8 Size of "DPFS" blob
0x28 8 Offset to the hash in DIFI (usually 0x010C)
0x30 8 Size of this hash
0x38 4 Flags (when this byte is non-zero, this is a DATA partition)
0x3C 8 File base offset (for DATA partitions)

IVFC

Start Length Description
0x00 4 Magic ("IVFC")
0x04 4 Magic Number (0x20000)
0x08 8 Unknown (0x20?)
0x10 8 First Hash Offset
0x18 8 First Hash Length
0x20 8 First Hash Block Size (1<<value)
0x28 8 Second Hash Offset
0x30 8 Second Hash Length
0x38 8 Second Hash Block Size (1<<value)
0x40 8 HashTable Offset
0x48 8 HashTable Length
0x50 8 HashTable Block Size (1<<value)
0x58 8 FileSystem Offset
0x60 8 FileSystem Length
0x68 8 FileSystem Block Size (1<<value)
0x70 8 Unknown (usually 0x78=120)
  • First & Second hash are not understood yet.

DPFS

Start Length Description
0x00 4 Magic ("DPFS")
0x04 4 Magic Number (0x10000)
0x08 8 Offset To First table
0x10 8 First table length
0x18 8 First table block size (1<<value)
0x20 8 Offset To Second table
0x28 8 Second table length
0x30 8 Second table block size (1<<value)
0x38 8 Offset to Data
0x40 8 Data Length
0x48 8 Data block size (1<<value)
  • Every block this table point to is written twice (concatenated). You can see that the offset to the next block is twice the length (except the data which always begin after 0x1000).

The first partition's data starts at 0x2000. First comes the hashtable (usually start @ 0x40 into the partition) and then the filesystem.

The hashtable entries' size is 2^x where x is the 'Hashed block size' from the IVFC block.

Hash

After the DIFI,IVFC & DPFS comes a 0x20 long hash, it is unknown what it's hashing.

Summary Drawing

 

The SAVE partition

  • The SAVE filesystem works with a backup. There are two SAVE blocks inside the partition concatenated. Which SAVE block is the updated one is unknown yet.. (I'm guessing from experience that (image[0x100B] & 0x20) == 0x20 --> 1st SAVE --Elisherer 01:30, 18 October 2011 (CEST))

Finding the folders table:

  • If DATA partition exists: At folder table exact offset from the SAVE struct (from the beginning of the struct).
  • Otherwise: The 'folder table offset' * 'folder table media' (=0x200) from the 'filestore offset'. (usually 0 from filebase)

Finding the files table:

  • If DATA partition exists: At file table exact offset from the SAVE struct (from the beginning of the struct).
  • Otherwise: The 'file table offset' * 'file table media' (=0x200) from the 'filestore offset'.

Detemining the filestore base:

  • If DATA partition exists: At file base from the DATA's DIFI struct into the DATA partition.
  • Otherwise: At the 'filestore offset' from the beginning of the SAVE struct.

Folder's entry structure: 

 struct folder_entry {
     u32 parent_folder_index;
     u8  filename[0x10];
     u32 folder_index;
     u32 unk1; 
     u32 last_file_index;
     u32 unk3; 
     u32 unk4;
 }

File's entry structure: 

 struct file_entry {
     u32 parent_folder_index;
     u8  filename[0x10];
     u32 index;
     u32 unk1; // magic?
     u32 block_offset;
     u64 file_size;
     u32 unk2; // flags?
     u32 unk3;
 }

The first entry in both tables is the count of the table, the parent directory index will be the amount of table rows. The root includes itself, so there are the amount - 1 (minus one) folders in the root directory (or files). The entries that follow after the root are the actual folders/files.

Reading the files out is as simple as taking the file base offset and adding (block_offset * 0x200) to it.

Here's a follow-up example from the Legend of Zelda: Ocarina of Time 3D: 

//FST entry = SAVE base + File base + (FST offset * 0x200) + (FST entry # * 0x30)
//0x2600    = 0x2000    + 0x400     + (0x1        * 0x200) + (0x0         * 0x30)

00002600: 03000000 09000000 00000000 00000000  ................
00002610: 00000000 00000000 00000000 00000000  ................
00002620: 00000000 00000000 00000000 00000000  ................
00002630: 01000000 73797374 656D2E64 61740000  ....system.dat..
00002640: 00000000 00000000 D57B1100 02000000  ........Õ{......
00002650: 22000000 00000000 E8121500 00000000  ".......è.......
00002660: 01000000 73617665 30302E62 696E0000  ....save00.bin..
00002670: 00000000 01000000 69921100 03000000  ........i’......
00002680: DC140000 00000000 04000000 00000000  Ü...............
Start Length Description
0x00 4 Magic ("SAVE")
0x04 4 Magic Number (0x40000)
0x08 8 Offset to data in this SAVE header(normally 0x20)
0x10 8 Partition Size [medias]
0x18 4 Partition Media Size
0x1C 8 Unknown
0x24 4 Unknown
0x28 8 FolderMap Offset
0x30 4 FolderMap Size
0x34 4 FolderMap Media Size
0x38 8 FileMap Offset
0x40 4 FileMap Size
0x44 4 FileMap Media Size
0x48 8 BlockMap Offset
0x50 4 BlockMap Size
0x54 4 BlockMap Media Size
0x58 8 File store offset (from SAVE)
0x60 4 File store length [medias]
0x64 4 File store media size
0x68 4/8 Folders Table offset (8 bytes in DATA)
0x6C 4 Folders Table Length (medias) (Only in no DATA)
0x70 4 Folders Table unknown
0x74 4 Folders Table Media size
0x78 4/8 Files Table offset (8 bytes in DATA)
0x7C 4 Files Table Length (medias) (Only in no DATA)
0x80 4 Files Table unknown
0x84 4 Files Table Media size
  • The FolderMap and FileMap still unknown. They are tables of uint32.
  • The BlockMap is a map of the blocks in the filestore. An entry in the BlockMap is 2 uint32: {uint32 start_block; uint32 end_block; }. This is still being researched. (You can use 3DSExplorer to see those maps.

Summary Drawing

 

Initialization

When a save FLASH contains all xFFFF blocks it's assumed uninitialized by the game cartridges and it initializes default data in place, without prompting the user.

I got a new game SplinterCell3D-Pal and I downloaded the save and it was 128KB of 0xFF, except the first 0x10 bytes which were the letter 'Z' (uppercase) --Elisherer 22:41, 15 October 2011 (CEST)

Fun Facts

If you have facts that you found out by looking at the binary files please share them here:

  • From one save to another the game backups the last files that were in the partition and the entire image header in "random" locations.. --Elisherer 22:41, 15 October 2011 (CEST)

Japanese

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