Gamecards

The 3DS gamecards have the same physical interface as regular DS and DSi gamecards. There is only a minor cosmetic difference in the plastic case, which has a small extruding notch on the top-right side. As such, it prevents insertion of the gamecard into old Nintendo DS or DSi systems.

When modifying the case so that the 3DS gamecard fits in a DS or DSi system, those systems will refuse to detect the gamecard and show no banner icon.

Savegame SPI flash transfers use CPOL=1 and CPHA=1. So far, only one savegame FLASH chip has been identified. The chip identifies as 0xC22211. The JEDEC manufacturer ID is Macronix, and despite the chip label saying 25L1001, the JEDEC ID matches the MX25L1021E. Datasheet at: 🔗 Macronix (Rev. 1.3, nov. 11, 2013) 🔗 Old version mirror (Rev. 0.01, apr. 07, 2010) However, the MX25L1021E doesn’t support the 4 bit wide transmission that the 3DS uses to talk to the SPI flash. It is thus likely that this is a custom flash chip.

Cartridges can come in several sizes and include system updates in a region reserved for this. In ROMs less than 1GB the update region can be found with: CART_SIZE_MAX-( 0x280000*(CART_SIZE_MAX/CART_SIZE_128MB) )-0x2000000. The region is then 0x2000000 bytes.

The communication protocol between the 3DS system and the 3DS gamecard has changed almost completely in comparison with the 🔗 DS and DSi gamecard communication protocol.

The protocol begins in a DS-compatible 8-byte command mode (unencrypted). It switches to a 3DS-only 16-byte mode (encrypted) after the 0x3e command. When 16-byte commands are used, the data bus maintains the value 0x00 until the card signals it is ready by clocking a single byte 0x01, followed by the actual data. After each 0x200-byte block of actual data, a 4-byte standard CRC32 of the block data (before encryption, polynomial 0x82608edb and the final output is xored with 0xffffffff) follows.

Here’s a set of sample gamecard commands for the title LEGO Star Wars III The Clone Wars (EUR), title ID 0004000000038c00, that a 3DS sends to a 3DS gamecard:

The header command has some initial dummy bytes, and eventually responds with the 0x200 byte InitialData. Here’s an example for Lego Starwars 3:

0000000: 00 8c 03 00 00 00 04 00 00 00 00 00 00 00 00 00  ................
0000010: b3 cf fb c6 6a b1 cb 20 32 af ce 35 d4 1c 74 c9  ....j.. 2..5..t.
0000020: 8e 6b 27 2f 08 01 28 3b d4 30 de 44 37 f5 b0 46  .k'/..(;.0.D7..F
0000030: 91 59 d7 38 33 48 df 83 fd 71 84 2c 00 00 00 00  .Y.83H...q.,....
0000040: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
0000050: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
0000060: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
0000070: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
0000080: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
0000090: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
00000a0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
00000b0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
00000c0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
00000d0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
00000e0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
00000f0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
0000100: 4e 43 43 48 7a 7f 0e 00 00 8c 03 00 00 00 04 00  NCCHz...........
0000110: 36 34 02 00 00 00 00 00 00 8c 03 00 00 00 04 00  64..............
0000120: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
0000130: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
0000140: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
0000150: 43 54 52 2d 50 2d 41 4c 47 50 00 00 00 00 00 00  CTR-P-ALGP......
0000160: 0c 27 e3 c1 de 7b 2a e2 d3 11 4f 32 a4 ee bf 46  .'...{*...O2...F
0000170: 9a fd 0c f3 52 c1 1d 49 84 c2 a9 f1 d2 14 4c 63  ....R..I......Lc
0000180: 00 04 00 00 00 00 00 00 00 00 00 00 01 03 00 00  ................
0000190: 05 00 00 00 01 00 00 00 00 00 00 00 00 00 00 00  ................
00001a0: 06 00 00 00 1c 0a 00 00 01 00 00 00 00 00 00 00  ................
00001b0: 22 0a 00 00 58 75 0e 00 01 00 00 00 00 00 00 00  "...Xu..........
00001c0: 13 0c 04 26 15 f6 47 c4 c6 32 25 ea 9e 67 f8 a2  ...&..G..2%..g..
00001d0: 7b 15 24 6b 88 fb c7 a9 27 25 7b 84 97 7b 78 7b  {.$k....'%{..{x{
00001e0: a6 5b ee 10 60 bb 6a 68 21 bb ce c6 00 03 5b 7e  .[..`.jh!.....[~
00001f0: 64 fb 6e ac a7 f0 96 0c fb 1f 5a 37 08 77 28 f7  d.n.......Z7.w(.

After the 0x82 command, cryptography is initialized, which can be reproduced following this algorithm; unless noted otherwise, all operations are in big endian byte order:

1. Set the AES keyslot 0x3b keyY to the values at 0x000:0x010. The corresponding keyX is set in Boot9.
2. Decrypt the 16 bytes at 0x010:0x020 using AES-128-CCM in keyslot 0x3b using the 12-byte nonce at 0x030:0x03c to obtain the primary seed; if the response to the 0xa0 command AND 0x00000003 equals 3, instead use slot 0x11 and set the normalkey to 0x00000000000000000000000000000000. Verify that the 16-byte tag at 0x020:0x030 is valid.
3. Split the primary seed into two halves: left and right.
4. Initialize a context for the SNOW 2.0 stream cipher. The 128-bit key is the primary seed. The 128-bit IV is a 128-bit static value depending on the gamecard ID2.
5. Call the SNOW 2.0 stream cipher 32 times to obtain 1024 bits (32 words) of output. Discard them.
6. Initialize a context for the RC4 stream cipher. The 256-bit key consists of a 128-bit static value depending on the gamecard ID2 followed by four outputs of the SNOW 2.0 stream.
7. Call the RC4 stream cipher 256 times to obtain 2048 bits (256 bytes) of output. Discard them.

All commands and responses are now encrypted using RC4. The gamecard controller and gamecard itself share the RC4 key and advance the state accordingly.

If the 0x83 command is sent, the cryptography is re-keyed:

1. Initialize a new context for the SNOW 2.0 stream cipher. The 128-bit key consists of the left half of the primary seed followed by the lower 64 bytes of the decrypted 0x83 command. The 128-bit IV is the same 128-bit static value depending on the gamecard ID2 as before.
2. Call the SNOW 2.0 stream cipher 32 times to obtain 1024 bits (32 words) of output. Discard them.
3. Initialize a new context for the RC4 stream cipher. The 256-bit key consists of the same 128-bit static value depending on the gamecard ID2 as before followed by four outputs of the new SNOW 2.0 stream.
4. Call the RC4 stream cipher 256 times to obtain 2048 bits (256 bytes) of output. Discard them.

The above example commands can be decrypted in this manner.

The static values are fixed in the gamecard controller and gamecards themselves, they are not obtained from Process9 or anywhere in NATIVE_FIRM.