Exploring Bluetooth for received signal strength indicator-based secret key extraction
Prarthana Lakshmane Gowda · 2012
Current approaches to secret key extraction using Received Signal Strength Indicator(RSSI) measurements mainly use the WiFi interface. However, in the presence of jammingadversaries and other interfering devices, the efficiency of RSSI-based secret key extractionusing WiFi degrades and sometimes the key extraction may even fail completely. A possiblemethod to overcome this problem is to collect RSSI measurements using the Bluetoothinterface. Bluetooth appears to be very promising for secret key extraction since theadaptive frequency hopping technique in Bluetooth automatically detects and avoids theuse of bad or interfering channels. In order to collect Bluetooth RSSI values, we design aprotocol where Alice and Bob use Google Nexus one phones to exchange L2CAP packets andthen we measure the RSSI for each received packet. We use a prequantization interpolationstep to reduce the probability of bit mismatches that are caused due to the inabililty tomeasure the time-duplex channel simultaneously by Alice and Bob. We then use the ASBGquantization scheme followed by information reconciliation and privacy amplification toextract the secret key bits. We conduct numerous experiments to evaluate the efficiencyof Bluetooth for secret key extraction under two di↵erent mobile environments - hallwaysand outdoors. The secret bit rates obtained from these experiments highlight that outdoorsettings are better suited for key extraction using Bluetooth when compared to hallwaysettings. Furthermore, we show that for very small distances such as 2 ft, the number ofconsecutive “0” RSSI values and bit mismatch is too high to extract any secret key bitsunder hallway settings. Finally, we also show that Bluetooth key extraction in outdoorsachieves secret bit rates that are comparable toWiFi, even when using lower transmit powerthan WiFi.