USER MANUAL
ESRPB / EDRPB - EASYFIT BLUETOOTH® SINGLE / DOUBLE ROCKER PAD
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F-710-017, V1.0
ESRPB / EDRPB User Manual | v1.3 | Jan 2018 | Page 15/68
4.4.2
Private resolvable source address mode
For some applications it is desirable to modify (rotate) the source address used by ExRPB in
order to prevent tracking of radio transmissions originating from a specific device. At the
same time, each such device must remain uniquely identifiable by the receiver.
To achieve these goals, ExRPB can be configured via NFC to use random resolvable private
addresses.
Using random resolvable private addresses requires that both ExRPB and the receiver both
know a common key – the so-called Identity Resolution Key (IRK). ExRPB uses its device-
unique random key as identity resolution key. This key can be configured via the NFC con-
figuration interface as described in chapter 6.
For resolvable private addresses, the 48 bit address field is split into two sub-fields:
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. Indi-
vidual advertising events used to transmit one telegram (as described in chapter 3)
use the same
prand
value.
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.