USER MANUAL
STM 550 / EMSI
–
ENOCEAN MULTISENSOR FOR IOT APPLICATIONS
© 2020 EnOcean | www.enocean.com F-710-017, V1.0
STM 550 / EMSI User Manual | v1.3 | September 2020 | Page 38/97
6.2
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)
◼
Rolling code size and current value
◼
Signature (MAC) size
◼
Security algorithm
Those parameters are communicated from STM 550 to the receiver during teach-in either via
a secure teach-in telegram, via NFC configuration or via the QR code of STM 550.
6.2.1
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.
6.2.2
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 the basis for encryption, decryption and authentication of telegrams.
6.2.3
Rolling code
The rolling code is a monotonously incrementing counter used to modify the encryption key
of secure telegrams as described in chapter 6.1.3. The rolling code is generated by the sender
and monitored by the receiver.
STM 550 uses by default a 32 bit rolling code counter which will be initialized to 0 at the time
of production and increment whenever a telegram is transmitted.
The receiver will store the most recently received rolling code value and only accept tele-
grams with higher rolling code values to avoid retransmission of previously transmitted mes-
sages.
6.2.4
Security algorithm
EMDC uses variable AES based on AES-128 to encrypt and authenticate its telegrams.