Vimar 03925, Руководство по установке

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Telegram format
4.4.2 Private resolvable source address mode
For some applications it is desirable to modify (rotate) the source address used by 03925 in order to prevent tracking of its radio transmissions. At the same
time, each 03925 device must remain uniquely identifiable by the receiver.
To achieve these goals, 03925 can be configured via NFC to use random resolvable private addresses.
Using random resolvable private addresses requires that both 03925 and the receiver both know a common key – the so-called Identity Resolution Key (IRK).
03925 uses its device-unique random key as identity resolution key. This key can be configured via the NFC configuration interface as described in chapter 6.
For resolvable private addresses, the 48 bit address field is split into two sub-fields:
■
prand
This field contains a random number which always starts (two most significant bits) with 0b10. The prand value is changed for each telegram that is transmit-
ted. Individual advertising events used to transmit one telegram (as described in chapter 3) use the same prand value.
■
hash
This field contains a verification value (hash) generated from prand using the IRK.
The structure of a random resolvable private address is shown in Figure 11 below.
prand (24 Bit)
hash (24 Bit)
0 1 Random Data (22 Bit)
MSB LSB
The prand value is encrypted using the IRK. The lowest 24 bit of the result (encrypted value) are then used as hash.
The concatenation of 24 bit prand and 24 bit hash will be transmitted as 48 bit private resolvable source address.
The receiving device maintains a list of IRK for all transmitters that have been commissioned to work with it.
Whenever the receiving device receives a radio telegram with private resolvable source address (identified by the most significant bits being set to 0b10), it will
itself generate a 24 bit hash from the 24 bit prand sequentially using the IRK of each device that it has been learned into it.
If an IRK matches (i.e. when prand is encoded with this specific IRK then the result matches hash), then the receiver has established the identity of the trans-
mitter.
So conceptually the IRK takes the role of the device source address while prand and hash provide a mechanism to select the correct IRK among a set of IRK.
This mechanism is illustrated in Figure 12 below.
Transmitter Receiver
prand (24 Bit) hash (24 Bit) prand (24 Bit) hash (24 Bit)
=?
Matching IRK
(Device Identity)
IRK (128 Bit)
IRK Device #1
IRK Device #2
IRK Device #3
…
IRK Device #n
4.5 Check Sum
The 3 byte BLE Check Sum is used to verify data integrity of received BLE radio telegrams.
It is calculated as CRC (cyclic redundancy check) of the BLE Header, Source Address and Payload fields.
Figure 11 – BLE private resolvable source address structure
Figure 12 – Resolving private source addresses