User's Manual

USER MANUAL

PTM 215B – 2.4 GHZ Pusbutton Transmitter Module

2.9.4.2 Private resolvable source address mode

For some applications it is desirable to modify (rotate) the source address used by PTM

215B in order to prevent tracking of its radio transmissions. At the same time, each PTM

215B device must remain uniquely identifiable by the receiver.

To achieve these goals, PTM 215B can be configured via NFC to use random resolvable pri-

vate addresses.

Using random resolvable private addresses requires that both PTM 215B and the receiver

both know a common key – the so-called Identity Resolution Key (IRK). PTM 215B uses its

device-unique random key as identity resolution key. This key can be configured via NFC

as described in chapter 2.11.

For resolvable private addresses, the 48 bit address field is split into two sub-fields:

n prand

This field contains a random number which always starts (two most significant bits) with

0b10. The prand value is changed for each telegram that is transmitted. Individual ad-

vertising events used to transmit one telegram (as described in chapter 2.5.1) use the

same prand value.

n hash

This field contains a verification value (hash) generated from prand using the IRK

The structure of a random resolvable private address is shown in Figure 11 below.

Figure 11 – BLE private resolvable source address structure

The prand value is encrypted using the IRK. The lowest 24 bit of the result (encrypted val-

ue) are then used as hash.

The concatenation of 24 bit prand and 24 bit hash will be transmitted as 48 bit private re-

solvable source address.