FrontLine BPA LOW ENERGY, Hardware User Manual

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A.1.6 Encrypting The Data Transmission
Data encryption begins with encrypting the link. The Session Key (SK) is created using a session key diversifier
(SKD). The first step in creating a SK is for the master device to send Link Layer encryption request message
(LL_ENC_REQ) that contains the SKD
master
. The SKD
master
is generated using the LTK. The slave receives
SKD
master
, generates SKD
slave
, and generates SK by concatenating parts of SKD
master
and SKD
slave
. The slave
device responds with an encryption response message (LL_ENC_RSP) that contains SKD
slave
; the master will
create the same SK.
Now that a SK has been calculated, the master and slave devices will now begin a handshake process. The
slave will transmit unencrypted LL_START_ENC_REQ, but sets the slave to receive encrypted data using the
recently calculated SK. The master responds with encrypted LL_START_ENC_RSP that uses the same SK just
calculated and setting the master to receive encrypted data. Once the slave receives the master’s encrypted
LL_START_ENC_RSP message and responds with an encrypted LL_START_ENC_RSP message the
Bluetooth
low energy devices can now begin transmitting and receiving encrypted data.
A.1.7 Decrypting Encrypted Data Using Frontline
®
BPA 600 low energy
Capture
Note: The following discussion uses the ComProbe BPA 600 in low energy capture mode
to illustrate how to identify the encryption process and to view decrypted data. However
any of the ComProbe devices (BPA 500, BPA low energy) that are low energy capable will
accomplish the same objectives, although the datasource setup will be slightly different
for each device.
A.1.7.1 Setting up the BPA 600
Figure 7 - ComProbe BPA 600 low energy only datasource
settings
1. Run the ComProbe Protocol Analysis
Software and select Bluetooth
Classic/low energy (BPA 600) . This will
bring up the BPA 600 datasource
window. This is where the parameters are
set for sniffing, including the devices to be
sniffed and how the link is to be decrypted.
2. Select
Devices Under Test
tab on the
Datasource window.
3. Click/select LE Only .
4. To decrypt encrypted data transmissions
between the Bluetooth low energy devices
the ComProbe analyzer needs to know the
LTK because this is the shared secret used
to encrypt the session. There are two ways
to provide this information and which to
select will depend on the pairing method:
Just Works or Passkey Entry .
TELEDYNE LECROY Appendicies
199 Frontline BPA low energy Hardware & Software User Manual