Gamecards

A 3DS gamecard

Close-up of PCB

Physical interface

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.

Pin	Name	Description
1	GND	Ground
2	CLK	Clock. Frequencies 6.7MHz and 4.2MHz for DS/DSi gamecards, up to 16.6MHz for 3DS gamecards (for both SPI and ROM transfers).
3	NC	Not connected. Possibly used to program cards.
4	RCS	ROM select, active low. Pulled low to start a ROM transfer.
5	RST	Reset, active low.
6	ECS	Savegame chip select, active low. Pulled low to start a savegame SPI transfer.
7	IRQ	Removal detection.
8	VCC	Powersupply 3.3V.
		ROM bus (selected by RCS)	Savegame bus (selected by ECS)
9	DAT0	Bidirectional data bus.	NC
10	DAT1
11	DAT2
12	DAT3
13	DAT4		NC/SIO3
14	DAT5		WP#/SIO2
15	DAT6		SO/SIO1
16	DAT7		SI/SIO0
17	GND	Ground

	3DS	DS and DSi
VCC	Only enabled when the power supply bits of CFG9_CARDSTATUS are set to 10	Always available when card is detected
Card-detect	Physical insertion switch, readable through CFG9_CARDSTATUS bit 0	IRQ pin
Time to first clock pulse	~280ms	~166ms

SPI flash

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.

Format

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.

Protocol

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:

Size	Command	Decrypted command	Description
2000	9F00000000000000	9F00000000000000	Reset
0000	71C93FE9BB0A3B18	71C93FE9BB0A3B18	Signal that the gamecard should act as a 3DS gamecard
0004	9000000000000000	9000000000000000	Get gamecard ID1, response=9000FEC2
0004	9000000000000000	9000000000000000	Get gamecard ID1, response=9000FEC2
0004	A000000000000000	A000000000000000	Get gamecard ID2, response=00000000
0000	3E00000000000000	3E00000000000000	Enter 16-byte command mode
0200	82000000000000000000000000000000	82000000000000000000000000000000	Get gamecard header and enable encryption
0000	F32C92D85C9D44DED3E0E41DBE7C90D9	8300000000000000708DF1A731717D0B	Seed (rekey cryptography)
0004	696B9D8582FB55D31B68CAFE70C74A95	A200000000000000708DF1A731717D0B	Get gamecard ID1 (using cryptography), response=9000FEC2
0004	BAA4812CA0AC9C5D19399530E3ACCCAB	A300000000000000708DF1A731717D0B	Get gamecard ID2 (using cryptography)
0000	178E427C22D87ADB86387249A97D321A	C500000000000000708DF1A731717D0B	Refresh cart NAND
0004	E06019B1BD5C9130ED6A4D9F4A9E7193	A200000000000000708DF1A731717D0B	Get gamecard ID1 (using cryptography), response=9000FEC2
0004	4E0D224862523BBFE2E6255F80E15F37	A200000000000000708DF1A731717D0B	Get gamecard ID1 (using cryptography), response=9000FEC2
0004	4CDF93D319FB62D0DB632A45E3E8D84C	A200000000000000708DF1A731717D0B	Get gamecard ID1 (using cryptography), response=9000FEC2
0004	9AA5D80551002F955546D296A57F0FEF	A200000000000000708DF1A731717D0B	Get gamecard ID1 (using cryptography), response=9000FEC2
0004	C12BA81AEF30DDDBD93FAD5D544C6334	A200000000000000708DF1A731717D0B	Get gamecard ID1 (using cryptography), response=9000FEC2
0200	62EC5FB7F420AE1DC6253AE18AFA5BB3	BF000000000000000000000000000000	Read gamecard at address 0
0200	E3FA23AA016BE0C93430D1F42FF41324	BF000000000040000000000000000000	Read gamecard at address 0x4000

The header command has some initial dummy bytes, and eventually responds with a 0x200 byte header. 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.