Teledyne LeCroy BTTracer_Trainer - BTTracer Users Manual - Manual (Page 180)

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BTTracer Protocol Analyzer User’s Manual CATC SW Version 2.20
• Retransmissions - This graph shows the rate of retransmitted
packets. In the Real-Time Statistics, a packet is evaluated as
'retransmitted' if at least one non-FHS seqn bit has already been
received and if the previous sequence bit is the same as the
current sequence bit. As the sequence bit toggles on data
payloads carrying CRC, the Real-Time Statistics tracks the seqn
bits in DM, DV, DH payload, and checks for correctness only if
the payload was correctly decoded without errors.
11.10 Encryption
Bluetooth encryption is a multi-staged process that provides devices with
secure, encrypted communications. The process begins with a device
prompting the user for a Personal Identification Number (PIN). When the
right PIN is entered, the Slave begins an encryption setup dialogue with the
Master. At the beginning of this dialogue, the Slave and the Master agree
on a Link Key. A Link Key is a 128-bit value that the two devices use for
authentication. When the Slave and Master agree on a Link Key, the Slave
then negotiates for the transfer of the Encryption Key from the Master
device. The Encryption Key is used to encrypt and decrypt messages. Once
the Encryption Key is transferred, both devices use it to encrypt all
subsequent communications.
In order for BTTracer to decode encrypted traffic, it needs the Link Key for
each Master-Slave connection for which encryption will be used. If you
know the Link Key, you can enter the Key into the Encryption Options
dialog box. If you do not know it, you give BTTracer the PIN for a device
and allow BTTracer to discover the Link Key on its own. Once BTTracer
has the Link Key, it can capture the rest of what it needs by listening to the
Master and Slave devices as they negotiate for the Encryption Key.
Note - The encryption settings here are for the BTTracer only. The
BTTrainer has its own encryption settings.
Note - There is no need to configure Encryption settings if BTTracer is used
to record BTTrainer traffic.
Configuring BTTracer for Encryption
For BTTracer to successfully decrypt traffic, two steps need to be
performed: 1) BTTracer needs to be given the PIN or Link Key for each
Master-Slave connection; and 2) Recording needs to be begun before the
Slave connects to the Master. If recording is begun prior to the creating the
Master-Slave connection, BTTracer will be able to obtain the encryption
key and decode encrypted traffic.