Teledyne Lecroy Frontline BPA 600, Hardware And Software User Manual, Page: 98 / 348

4.3.1.11.2 Bluetooth low energy Data Encryption/Master and Slave
Assignment
A Bluetooth low energy data connection consists of connection events, which are a series of transmissions on
the same channel. In each connection event the master transmits first, then the slave, and then the devices
take turns until the connection event is finished.
When the data connection is encrypted and the packets are successfully decrypted, the sniffer can determine
exactly who sent which packet (only non-empty, encrypted packets – empty packets are never encrypted).
These packets are labeled either ‘M’ for master or ‘S’ for slave.
When the data connection is unencrypted or when encrypted packets are not successfully decrypted by the
sniffer, the sniffer cannot distinguish the two devices’ (master and slave) packets by their content, just by the
packet timing. In those cases we label each device as side ‘1’ or ‘2’, not as master or slave. In each
connection event, packets sent by the device which transmitted first in the connection event are labeled ‘1’,
and packets sent by the device which transmitted second are labeled ‘2’.
If no packets in the connection event are missed by the sniffer, the device labeled ‘1’ is the master and the
device labeled ‘2’ is the slave. However, if we do not capture the very first packet in a connection event (i.e.
the packet sent by the master) but do capture the packet sent by the slave, we label the slave as side ‘1’ since
it is the first device we heard in the connection event. Because there is potential clock drift since the last
connection event, we cannot use the absolute timing to correct this error; there would still be cases where
we get it wrong. Therefore we always assign ‘1’ to the first packet in a connection event. So even though it is
rare, there are connection events where packets sent by the slave device are labeled ‘1’ and packets sent by
the master are labeled ‘2’.
Finally, in a noisy environment it is also possible that the sniffer does not capture packets in the middle of a
connection event. If this occurs and the sniffer cannot determine the side for the remaining packets in that
connection event, the side is labeled ‘U’ for “unknown”.
4.3.1.11.3 Bluetooth low energy Decryption Status
Occasionally you may have a packet with an event status of “received without errors,” but a decryption status
of “unable to decrypt.” There are three main causes for this, and in order of likelihood they are:
1. Wrong Long-Term Key – having the wrong long-term key will cause this error, so the first thing to
check is that your long term key is entered correctly in the datasource settings.
2. Dropped Packets – Too much interference with a ComProbe device will cause dropped packets and
may cause this error. As a rule of thumb, it is always a good idea to ensure the ComProbe device is
positioned away from sources of interference, and is placed in between the two devices being sniffed.
3. Faulty Device – although the chances of this are low, it is possible that a device is not encrypting
packets properly. This is likely to happen only if you are a firmware developer working on encryption.
4.3.1.11.4 Customizing Fields in the Summary Pane
You can modify the Summary Pane in Frame Display .
Summary pane columns can be reordered by dragging any column to a different position.
Fields from the
Decode
pane can be added to the summary pane by dragging any
Decode
pane field to the
desired location in the
summary
pane header. If the new field is from a different layer than the summary
pane a plus sign (+) is prepended to the field name and the layer name is added in parentheses. The same
field can be added more than once if desired, thus making it possible to put the same field at the front and
back (for example) of a long header line so that the field is visible regardless of where the header is scrolled
to.
An added field can be removed from the Summary pane by selecting Remove New Column from the
right-click menu.
Chapter 4 Capturing and Analyzing Data TELEDYNE LECROY
Frontline BPA 600 Hardware & Software User Manual 90