The Nintendo NFC adapter is an upcoming external device which adds NFC capabilities for amiibos to old Nintendo 3DS and Nintendo 2DS consoles, using the infrared port on the back of the console.
Technical details
Based on analysis of the fangate_updater.bin file, which is part of the old Nintendo 3DS operating system since 9.3.0-21 and contains the firmware running on the external adapter; and analysis of the NFC Services running on old 3DS.
- SOC inside the adapter: Broadcom BCM20791B1
- CPU: ARM Cortex M0
- Communications: infrared, with ir:USER running on the console. Uses obfuscated payloads. Baud rate is 115200 bps.
Memory map:
| Address | Size | Description |
|---|---|---|
| 0x08008000 | 256KB? | Firmware (fangate_updater.bin) |
| 0x20000000 | 128KB? | RAM |
| 0x40023C00 | 0x1C | FLASH ROM control |
| 0xE000ED00 | 0x104 | ARM Cortex system control block |
IR communications
Packets are sent using IrDA-SIR (using ir:USER), with a 8N1 encoding (eight data bits, one stop bit, without parity). Each one is formed by a 2-byte header, a varint with the payload size, an obfuscated payload, and trailing error detection byte.
Layer 1 - framing format
Frames are encoded using two different yet very simmilar formats, depending on how large the payload to be transmitted is:
- For payloads with less than 64 bytes, the third byte represents the payload size.
- For packets with up to 16383 bytes, the size is split in two bytes, with the third byte being the upper 6 bits of the payload size, OR'd with 0x40, and the fourth being the lower eight bits of the payload size
| Byte | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
|---|---|---|---|---|---|---|---|---|
| 0x00 | Synchronization byte (0xA5)
| |||||||
| 0x01 | Reserved for future use (0x00)
| |||||||
| 0x02 | RFU (0)
|
Short frame (0)
|
Payload size | |||||
| 0x03 | Payload byte 0 | |||||||
| ... | ||||||||
| 0x03+n-1 | Payload byte n-1 | |||||||
| 0x03+n | CRC-8-CCITT computer over whole packet | |||||||
| Byte | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
|---|---|---|---|---|---|---|---|---|
| 0x00 | Synchronization byte: 0xA5
| |||||||
| 0x01 | Reserved for future use | |||||||
| 0x02 | RFU (0)
|
Long frame (1)
|
Payload size (upper 6 bits) | |||||
| 0x03 | Payload size (lower 8 bits) | |||||||
| 0x04 | Payload byte 0 | |||||||
| ... | ||||||||
| 0x04+n-1 | Payload byte n-1 | |||||||
| 0x04+n | CRC-8-CCITT computer over whole packet | |||||||
Header
The packet header is fixed and consists in a synchronization byte (0xA5), followed by a unused (possibly RFU) zero byte. After these two hardcoded bytes, there's a varint representing the payload size, which may use one byte or two, depending on the how big the payload is.
In C:
uint8_t * setPacketHeader(uint8_t * buffer, size_t payloadSize) {
assert(payloadSize < 16384);
buffer[0] = 0xA5;
buffer[1] = 0x00;
if (payloadSize < 64) {
buffer[2] = payloadSize;
buffer += 3;
} else {
buffer[2] = 0x40 | (payloadSize >> 8);
buffer[3] = payloadSize;
buffer += 4;
}
return buffer;
}
Payload
The payload is obfuscated using a XOR-based encryption. In C:
void payloadObfuscate(const void * voidplain, void * voidcipher, size_t size) {
uint16_t * plain = (uint16_t *) voidplain;
uint16_t * cipher = (uint16_t *) voidcipher;
size_t halfCount = size / sizeof(uint16_t);
uint16_t xorval = htobe16(0xE963);
size_t i;
for (i = 0; i < halfCount; i++) {
xorval ^= plain[i];
cipher[i] = xorval;
}
}
void payloadDeobfuscate(const void * voidcipher, void * voidplain, size_t size) {
uint16_t * cipher = (uint16_t *) voidcipher;
uint16_t * plain = (uint16_t *) voidplain;
size_t halfCount = size / sizeof(uint16_t);
if (halfCount) {
size_t i;
for (i = halfCount - 1; i > 0; i--) {
plain[i] = cipher[i] ^ cipher[i - 1];
}
plain[0] = cipher[0] ^ htobe16(0xE963);
}
}
Error detection
The trailing error detection byte is calculated using CRC-8-CCITT over the whole packet (both the header and the payload)
Layer 2 - "ircom"
ircom is a simple stateful point-to-point master-slave communication protocol built on top of IR layer 1.
| Byte | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
|---|---|---|---|---|---|---|---|---|
| 0x00 | Random value in range 0x01~0xFE
| |||||||
| 0x01 | Random value in range 0x01~0xFE
| |||||||
| 0x02 | Random value in range 0x01~0xFE
| |||||||
| 0x03 | Random value in range 0x01~0xFE
| |||||||
| 0x04 | RFU? | Protocol version: 0x1
| ||||||
| 0x05 | Connection identifier | |||||||
| 0x06 | Reserved for future use? | |||||||
| 0x07 | ??? | Operation code | ||||||
| 0x08+ | Payload (if any) | |||||||
- Random values are generated using a Mersenne Twister whose seed is based off the NFC adapter system tick counter. It is therefore random, and the 3DS won't attempt to validate them by any means. Its purpose is unknown.
- NFC adapter will ignore packets whose protocol version is not 1. It will not even reply.
- Connection identifier is a random byte the 3DS assigns to identify the connection should be several connections in range at once. Slave devices must save this value from the initial handshake packet and use it for replies. It must also ignore packets whose connection ID does not match.
Operation codes
| Code | Name | Has payload | Direction |
|---|---|---|---|
| 0x0 | Layer 3 command? | Yes | Master to slave |
| 0x1 | ??? | ??? | |
| 0x2 | ??? | ??? | |
| 0x3 | ??? | ??? | |
| 0x4 | ??? | ??? | |
| 0x5 | ??? | ??? | |
| 0x6 | ??? | ??? | |
| 0x7 | ??? | ??? | |
| 0x8 | ??? | ??? | |
| 0x9 | ??? | ??? | |
| 0xA | Disconnect request | No | Master to slave |
| 0xB | Disconnection acknowledgment | No | Slave to master |
| 0xC | Handshake | No | Master to slave |
| 0xD | Handshake acknowledgement | No | Slave to master |
| 0xE | ??? | ??? | |
| 0xF | ??? | ??? |
Samples
NFC handshake beacons:
| Layer 1 packet | Layer 2 packet | Layer 3 packet |
|---|---|---|
A5 00 08 73 FE A5 C4 A4 2C A4 20 F5
|
9A 9D D6 3A 01 E8 00 0C
|
␀ |
A5 00 08 D1 3E B7 7B B6 91 B6 9D 87
|
38 5D 66 45 01 EA 00 0C
|
␀ |
A5 00 08 09 58 23 36 22 DA 22 D6 AE
|
E0 3B 2A 6E 01 EC 00 0C
|
␀ |
A5 00 08 5E DD A4 A0 A5 4E A5 42 A8
|
B7 BE FA 7D 01 EE 00 0C
|
␀ |
A5 00 08 BC 19 C6 37 C7 C7 C7 CB 8B
|
55 7A 7A 2E 01 F0 00 0C
|
␀ |
A5 00 08 C9 15 F6 63 F7 91 F7 9D B2
|
20 76 3F 76 01 F2 00 0C
|
␀ |
A5 00 08 6E 48 47 1A 46 EE 46 E2 C7
|
87 2B 29 52 01 F4 00 0C
|
␀ |
A5 00 08 A2 8C E5 C3 E4 35 E4 39 74
|
4B EF 47 4F 01 F6 00 0C
|
␀ |
A5 00 08 26 1C 07 10 06 E8 06 E4 64
|
CF 7F 21 0C 01 F8 00 0C
|
␀ |
A5 00 08 7E 73 A2 3F A3 C5 A3 C9 FD
|
97 10 DC 4C 01 FA 00 0C
|
␀ |
A5 00 08 75 00 F3 B8 F2 44 F2 48 63
|
9C 63 86 B8 01 FC 00 0C
|
␀ |
A5 00 08 8D AC 0F D5 0E 2B 0E 27 72
|
64 CF 82 79 01 FE 00 0C
|
␀ |
A5 00 08 A3 55 7C 53 7D 52 7D 5E B2
|
4A 36 DF 06 01 01 00 0C
|
␀ |
A5 00 08 15 06 43 C0 42 C3 42 CF 85
|
FC 65 56 C6 01 03 00 0C
|
␀ |
A5 00 08 66 E0 9A 17 9B 12 9B 1E A0
|
8F 83 FC F7 01 05 00 0C
|
␀ |
A5 00 08 A4 35 09 97 08 90 08 9C 25
|
4D 56 AD A2 01 07 00 0C
|
␀ |
A5 00 08 73 E2 BD AF BC A6 BC AA 60
|
9A 81 CE 4D 01 09 00 0C
|
␀ |
A5 00 08 02 57 D7 B0 D6 BB D6 B7 28
|
EB 34 D5 E7 01 0B 00 0C
|
␀ |
A5 00 08 0D 79 01 AA 00 A7 00 AB 22
|
E4 1A 0C D3 01 0D 00 0C
|
␀ |
A5 00 08 14 91 04 B9 05 B6 05 BA B2
|
FD F2 10 28 01 0F 00 0C
|
␀ |
A5 00 08 2C 86 B1 49 B0 58 B0 54 C0
|
C5 E5 9D CF 01 11 00 0C
|
␀ |
A5 00 08 D5 1D DE DB DF C8 DF C4 F9
|
3C 7E 0B C6 01 13 00 0C
|
␀ |
A5 00 08 AF 75 DE 5C DF 49 DF 45 9C
|
46 16 71 29 01 15 00 0C
|
␀ |
A5 00 08 C8 E2 5B C6 5A D1 5A DD B5
|
21 81 93 24 01 17 00 0C
|
␀ |
A5 00 08 9B 51 68 2D 69 34 69 38 41
|
72 32 F3 7C 01 19 00 0C
|
␀ |
A5 00 08 13 7B 9F EF 9E F4 9E F8 32
|
FA 18 8C 94 01 1B 00 0C
|
␀ |
A5 00 08 A7 62 02 9C 03 81 03 8D BD
|
4E 01 A5 FE 01 1D 00 0C
|
␀ |
A5 00 08 39 06 94 36 95 29 95 25 09
|
D0 65 AD 30 01 1F 00 0C
|
␀ |
A5 00 08 32 4C D7 C0 D6 E1 D6 ED 92
|
DB 2F E5 8C 01 21 00 0C
|
␀ |
A5 00 08 83 BE F2 8F F3 AC F3 A0 B1
|
6A DD 71 31 01 23 00 0C
|
␀ |
A5 00 08 83 5E A0 57 A1 72 A1 7E F0
|
6A 3D 23 09 01 25 00 0C
|
␀ |
A5 00 08 6E C8 AD 69 AC 4E AC 42 D1
|
87 AB C3 A1 01 27 00 0C
|
␀ |
A5 00 08 C7 33 A1 2C A0 05 A0 09 FC
|
2E 50 66 1F 01 29 00 0C
|
␀ |