USER MANUAL
EMDCB
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BLUETOOTH LOW ENERGY MOTION AND ILLUMINATION SENSOR
© 2019 EnOcean | www.enocean.com
EMDCB User Manual | v1.3 | August 2019 | Page 30/67
5.1
Authentication implementation
EMDCB implements telegram authentication based on AES128 in CCM (Counter with CBC-
MAC) mode as described in IETF RFC3610. At the time of writing, the RFC3610 standard
could be found here:
https://www.ietf.org/rfc/rfc3610.txt
The 13 Byte CCM Nonce (number used once
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unique) initialization value is constructed as
concatenation of 6 byte Source Address, 4 byte Sequence Counter and 3 bytes of value
0x00 (for padding).
Note that both Source Address and Sequence Counter use little endian format (least signifi-
cant byte first).
Figure 21 below shows the structure of the AES128 Nonce.
Figure 21
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AES128 Nonce structure
The AES128 Nonce and the 128 bit device-unique security key are then used to calculate a
32 bit signature of the authenticated telegram payload shown in Figure 22 below.
Figure 22
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Authenticated payload
The calculated 32 bit signature is then appended to the data telegram payload as shown in
in chapter 4.6
Appendix B gives a step by step example how to authenticate the payload of a received
data telegram based on the previously exchanged security key.
