Exploring bluetooth for received signal strength indicator-based secret key extraction

Current approaches to secret key extraction using Received Signal Strength Indicator (RSSI) measurements mainly use the WiFi interface. However, in the presence of jamming adversaries and other interfering devices, the efficiency of RSSI-based secret key extraction using WiFi degrades and sometimes the key extraction may even fail completely. A possible method to overcome this problem is to collect RSSI measurements using the Bluetooth interface. Bluetooth appears to be very promising for secret key extraction since the adaptive frequency hopping technique in Bluetooth automatically detects and avoids the use of bad or interfering channels. In order to collect Bluetooth RSSI values, we design a protocol where Alice and Bob use Google Nexus one phones to exchange L2CAP packets and then we measure the RSSI for each received packet. We use a prequantization interpolation step to reduce the probability of bit mismatches that are caused due to the inabililty to measure the time-duplex channel simultaneously by Alice and Bob. We then use the ASBG quantization scheme followed by information reconciliation and privacy amplification to extract the secret key bits. We conduct numerous experiments to evaluate the efficiency of Bluetooth for secret key extraction under two di↵erent mobile environments - hallways and outdoors. The secret bit rates obtained from these experiments highlight that outdoor settings are better suited for key extraction using Bluetooth when compared to hallway settings. Furthermore, we show that for very small distances such as 2 ft, the number of consecutive "0" RSSI values and bit mismatch is too high to extract any secret key bits under hallway settings. Finally, we also show that Bluetooth key extraction in outdoors achieves secret bit rates that are comparable toWiFi, even when using lower transmit power than WiFi.