Ir:USER

This service was added with 2.0.0-2. It employs a custom packet format with obfuscation and error detection.

Command set

When sending data, SendIrnop is used when the size is <=0xFC, otherwise SendIrnopLarge is used.

Command Header	Available since system version	Description
0x00010182	2.0.0-2	InitializeIrnop
0x00020000	2.0.0-2	FinalizeIrnop
0x00030000	2.0.0-2	ClearReceiveBuffer
0x00040000	2.0.0-2	ClearSendBuffer
0x0005....	2.0.0-2	WaitConnection
0x00060040	2.0.0-2	RequireConnection (u8 input)
0x0007....	2.0.0-2	AutoConnection
0x0008....	2.0.0-2	AnyConnection
0x00090000	2.0.0-2	Disconnect
0x000A0000	2.0.0-2	GetReceiveEvent (writes event handle to cmdreply[3])
0x000B0000	2.0.0-2	GetSendEvent (writes event handle to cmdreply[3])
0x000C0000	2.0.0-2	GetConnectionStatusEvent (writes event handle to cmdreply[3])
0x000D0042	2.0.0-2	SendIrnop (u32 size, ((Size<<14) | 2), inbufptr)
0x000E0042	2.0.0-2	SendIrnopLarge (u32 size, ((Size<<8) | 10), inbufptr)
0x000F....	2.0.0-2	ReceiveIrnop
0x0010....	2.0.0-2	ReceiveIrnopLarge
0x0011....	2.0.0-2	GetLatestReceiveErrorResult
0x0012....	2.0.0-2	GetLatestSendErrorResult
0x0013....	2.0.0-2	GetConnectionStatus
0x0014....	2.0.0-2	GetTryingToConnectStatus
0x0015....	2.0.0-2	GetReceiveSizeFreeAndUsed
0x0016....	2.0.0-2	GetSendSizeFreeAndUsed
0x0017....	2.2.0-X	GetConnectionRole
0x00180182	2.2.0-X	InitializeIrnopShared (u32, u32, u32, u32, u32, u8, 0, handle)
0x00190040	2.2.0-X	ReleaseReceivedData (32bit_value input)
0x001A0040	2.2.0-X	SetOwnMachineId (u8 input)

Protocol description

Packets are sent using IrDA-SIR, 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.

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.

• 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

For packets with less than 64 bytes:

Sync	RFU	Size
0xA5	0x00	size

For packets with up to 16383 bytes:

Sync	RFU	Size (1)	Size (2)
0xA5	0x00	(size >> 8) | 0x40	size & 0xFF

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)