User manual

Figure 6 - Encryption Response from Slave, Example (ComProbe
Frame Display, BPA 600 low energy capture)
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.
TELEDYNE LECROY Appendicies
215 Frontline BPA low energy Hardware & Software User Manual