USER MANUAL
STM 550X / EMSIX
–
ENOCEAN MULTI-SENSOR
© 2020 EnOcean | www.enocean.com F-710-017, V1.0
STM 550x / EMSIx User Manual | v1.0 | February 2020 | Page 35/79
5.2
Security parameters
The following security parameters are used to define secure communication based on
EnOcean Alliance security specification between a sender and a receiver:
◼
EURID (Device ID of the sender)
◼
Security Key of the sender
◼
Rolling Code and signature (CMAC) type
Those parameters are communicated from STM 550x to the receiver during teach-in either
via a secure teach-in telegram, via NFC configuration or via the QR code of STM 550x.
5.2.1
EURID
The EURID identifies the sender of each radio telegram using a unique 6 byte value. The
EURID of an EnOcean device is assigned at manufacturing and cannot be changed.
5.2.2
Security key
The security key is a random 128 Bit (16 byte) value that is known only to the sender and
the receiver(s). It is used to encrypt, decrypt and authenticate telegrams.
5.2.3
Rolling code and signature (CMAC) type
The rolling code is a monotonously incrementing counter used to modify the content of secure
telegrams. The rolling code is generated by the sender and monitored by the receiver.
The receiver will store the most recently received rolling code value and only accept tele-
grams with higher rolling code counter values to avoid retransmission of previously transmit-
ted messages.
The signature (CMAC) is generated based on the combination of telegram payload, rolling
code and security key. It is unique for each telegram meaning that even two consecutive
telegrams with the same payload will have different CMAC signatures due to using different
rolling code counter values.
Rolling code and signature type are specified using the security level format (SLF) register
that is transmitted as part of the secure teach-in telegram.
