USER MANUAL
PTM 216B – BLUETOOTH
®
PUSHBUTTON TRANSMITTER MODULE
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F-710-017, V1.0
PTM 216B User Manual | v1.0 | February 2022 | Page 23/86
4.7.1
Authentication implementation
PTM 216B implements data telegram authentication based on AES128 in CCM (Counter with
CBC-MAC) mode as described in IETF RFC3610. At the time of writing, the RFC3610 stand-
ard could be found here:
https://www.ietf.org/rfc/rfc3610.txt
The 13 Byte CCM Nonce (number used once – 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 18 below shows the structure of the AES128 Nonce.
Figure 18 – 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 19 below.
Figure 19 – Authenticated payload
The calculated 32 bit signature is then appended to the data telegram payload as shown in
Figure 14 in chapter 4.6.
In addition to the RFC3610 standard itself, please consult also Appendix C for a step by
step description of the authentication process.
