smarthomatic

SHC Proxy

Proxy

Purpose

The SHC proxy can forward packets between other devices when their distance is too high to have a reliable communication. The proxy doesn't just duplicate all packets automatically (acting as a repeater), but only forwards packets when one of the rules defined in the e2p matches and also translates the device IDs and AES keys. This is to avoid sending unnecessary packets and raising the general risk of collisions. It's assumed that only a small amount of devices can't be reached from the base station typically, so the number of rules is currently limited to 16 and each rule is only for a specific device ID.

Functions, Behavior

The proxy listens for all packets and tries to decrypt them with one of the AES keys defined in e2p. When decryption is successful, Sender ID and Receiver ID are compared to the rules. When they match, the packet is modified according rule definition and sent out using the (most probably differently) defined AES key number from the rule.

Like all other smarthomatic devices, the proxy also sends (roughly once per day) a DeviceInfo message to describe the own Device ID and version. This is always encrypted using the AES key defined in the generic block of the e2p.

In the following example, a device with ID 1045 can be reached form the base station using Device ID 45. The proxy takes the packet and translates between base station and the device. The base station can't reach the device 1045 directly, since it doesn't know its AES key and therefore ignores the original packet in case it would be received despite it's usually too far away to receive it.

Sender ID	Receiver ID	New Sender ID	New Receiver ID	AES Key Number
0	45	0	1045	2
1045	0	45	0	0

Example rule configuration from e2p

Supported Messages

Generic_DeviceInfo_Status

E2P Device Configuration

Offset	Block	Content	Type	Size	Description
0	Hardware Values for hardware setup, which have no special meaning to SHC device concepts + the DeviceType, which decides about the existence of further blocks.	DeviceType	EnumValue	1 Bytes	The device can check with this value if the EEPROM data is meant for the actual type of device. If not, the device goes into an error mode. Values: 0 = BaseStation, 10 = Proxy, 20 = EnvSensor, 40 = PowerSwitch, 45 = Controller, 50 = RGBDimmer, 60 = Dimmer, 70 = SoilMoistureMeter, 80 = Thermostat, 90 = TeaMaker
8		OsccalMode	IntValue	1 Bytes	This value is used to change the speed of the internal oscillator. 0 = don't use OSCCAL calibration (e.g. external crystal oszillator is used). -128 = OSCCAL measure mode: the LED blinks every 60s, so the user can measure the original speed. -127..+127 = The speed is adjusted by the given amount in per mill (e.g. 10 means to speed up the device by +1%). MinVal: -128, MaxVal: 127, Default: 0
16		Reserved		6 Bytes	n/a
64	Generic This block contains SHC configuration data which every device has.	DeviceID	UIntValue	12 Bits	The DeviceID identifies the specific unit in the SHC network. It is used to address the device and in messages the device sends. Every device has to have a different DeviceID. MinVal: 0, MaxVal: 4095
76		Reserved		4 Bits	n/a
80		PacketCounter	UIntValue	3 Bytes	The PacketCounter is counted up throughout the whole lifetime of the device and is used to make the encrypted packets differently from each other every time. MinVal: 0, MaxVal: 16777215
104		Reserved		19 Bytes	n/a
256		AesKey	ByteArray	32 Bytes	This key is used to encrypt packets before sending and also used as primary key to decrypt packets. Special devices may have additional keys in their device specific block.
512	Proxy This block contains the specific configuration data that only Proxy devices need.	AesKeyCount	UIntValue	1 Bytes	This is the number of AES keys to use from the AesKeys block. Limit the number to the needed amount to avoid that the base station tries decoding with every one. MinVal: 1, MaxVal: 16, Default: 1
520		AesKey	ByteArray[16]	32 Bytes x 16	These are all AES keys which can be used to encrypt or decrypt packages at the base station.
4616		TransceiverWatchdogTimeout	UIntValue	1 Bytes	Reset RFM12B module if no data is received until timeout is reached. Use this function if your specific transceiver hangs sometimes. Value is in deca seconds. Suggested setting is 48 (for 8 minutes). Set 0 to disable. MinVal: 0, MaxVal: 255, Default: 48
4624		SenderID	UIntValue[16]	2 Bytes x 16	These are the Sender Device IDs of the packets that shall be forwarded. Each index corresponds to the values of the following arrays with the same index. The first index with same SenderID and ReceiverID (e.g. 0) is marking from where on the entries are not considered anymore. MinVal: 0, MaxVal: 4095, Default: 0
4880		ReceiverID	UIntValue[16]	2 Bytes x 16	These are the Receiver Device IDs of the packets that shall be forwarded. MinVal: 0, MaxVal: 4095, Default: 0
5136		NewSenderID	UIntValue[16]	2 Bytes x 16	These are the (modified) Sender IDs that are used in the forwarded packets. MinVal: 0, MaxVal: 4095, Default: 0
5392		NewReceiverID	UIntValue[16]	2 Bytes x 16	These are the (modified) Receiver IDs that are used in the forwarded packets. MinVal: 0, MaxVal: 4095, Default: 0
5648		AesKeyNumber	UIntValue[16]	1 Bytes x 16	These are the AES key numbers used for the (modified) forwarded packets. MinVal: 0, MaxVal: 15, Default: 0
5776		Reserved		302 Bytes	n/a