USER MANUAL PREVIEW
PTM 535BZ
–
BLUETOOTH AND ZIGBEE GREEN POWER PUSHBUTTON TRANSMITTER
© 2021 EnOcean | www.enocean.com
F-710-017, V1.0
PTM 535BZ User Manual | v1.0 | May 2021 | Page 24/112
3.4.2
BLE data telegram authentication
PTM 535BZ implements telegram authentication for transmitted BLE data telegrams to en-
sure that only telegrams from transmitters using a previously exchanged security key will
be accepted by the receiver.
Authentication of BLE data telegrams relies on a 32 bit telegram signature which is calcu-
lated as shown in
below and exchanged as part of the radio telegram. This mech-
anism is identical to the mechanism used in PTM 215B.
Figure 16
–
Telegram authentication flow
Sequence counter, source address and the remaining telegram data together form the input
data for the signature algorithm. Input data and the device-unique 128 bit security key are
used as input to the RFC3610 algorithm
which generates a 32 bit signature. This signature
which will be transmitted as part of the radio telegram.
The signature is therefore dependent both on the current value of the sequence counter, the
device source address and the telegram payload. Changing any of these three parameters
will therefore result in a different signature.
The receiver performs the same signature calculation based on sequence counter, source
address and the remaining telegram data of the received telegram using the security key it
received from PTM 535BZ during commissioning.
The receiver then compares the signature reported as part of the telegram with the signature
it has calculated. If these two signatures match, then the receiver knows that the transmitter
(PTM 535BZ) and receiver possess the same security key and that the message content
(address, sequence counter, data) has not been modified.
In order to avoid message replay (capture and retransmission of a valid message), it is re-
quired that the receiver tracks the value of the sequence counter used by PTM 535BZ and
only accepts messages with higher sequence counter values (i.e. not accepts equal or lower
sequence counter values for subsequent telegrams).
By default, the factory programmed SECURITY_KEY1 is used for data telegram authentication
and resolvable private address generation as described in
Chapter 3.3.5.2
. It is possible to
configure PTM 535BZ via NFC (as described in
Chapter 5.6.4)
to use SECURITY_KEY2 instead
of SECURITY_KEY1.
