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.
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.
We evaluate the effectiveness of secret key extraction, for private communication between two wireless devices, from the received signal strength (RSS) variations on the wireless channel between the two devices. We use real world measurements of RSS in a variety of environments and settings. The results from our experiments with 802.11-based laptops show that in certain environments, due to lack of variations in the wireless channel, the extracted bits have very low entropy making these bits unsuitable for a secret key, an adversary can cause predictable key generation in these static environments, and in dynamic scenarios where the two devices are mobile, and/or where there is a significant movement in the environment, high entropy bits are obtained fairly quickly. Building on the strengths of existing secret key extraction approaches, we develop an environment adaptive secret key generation scheme that uses an adaptive lossy quantizer in conjunction with Cascade-based information reconciliation and privacy amplification. Our measurements show that our scheme, in comparison to the existing ones that we evaluate, performs the best in terms of generating high entropy bits at a high bit rate. The secret key bit streams generated by our scheme also pass the randomness tests of the NIST test suite that we conduct. We also build and evaluate the performance of secret key extraction using small, low-power, hand-held devices-Google Nexus One phones-that are equipped 802.11 wireless network cards. Last, we evaluate secret key extraction in a multiple input multiple output (MIMO)-like sensor network testbed that we create using multiple TelosB sensor nodes. We find that our MIMO-like sensor environment produces prohibitively high bit mismatch, which we address using an iterative distillation stage that we add to the key extraction process. Ultimately, we show that the secret key generation rate is increased when multiple sensors are involved in the key extraction process.
We evaluate the effectiveness of secret key extraction, for private communication between two wireless devices, from the received signal strength (RSS) variations on the wireless channel between the two devices. We use real world measurements of RSS in a variety of environments and settings. Our experimental results show that (i) in certain environments, due to lack of variations in the wireless channel, the extracted bits have very low entropy making these bits unsuitable for a secret key, (ii) an adversary can cause predictable key generation in these static environments, and (iii) in dynamic scenarios where the two devices are mobile, and/or where there is a significant movement in the environment, high entropy bits are obtained fairly quickly. Building on the strengths of existing secret key extraction approaches, we develop an environment adaptive secret key generation scheme that uses an adaptive lossy quantizer in conjunction with Cascade-based information reconciliation [7] and privacy amplification [14]. Our measurements show that our scheme, in comparison to the existing ones that we evaluate, performs the best in terms of generating high entropy bits at a high bit rate. The secret key bit streams generated by our scheme also pass the randomness tests of the NIST test suite [21] that we conduct.
In this paper, we evaluate the effectiveness of secret key extraction from the Received signal strength (RSS) variations on the wireless channel between the two devices for private communication between them. We use real world measurements of RSS in a variety of environments and settings. The results from our experiments with 802.11-based laptops show that 1)An adversary can cause predictable key generation in these static environments, and 2)In dynamic scenarios where the two devices are mobile, high entropy bits are obtained . Building on the strengths of existing secret key extraction approaches, we develop an environment adaptive secret key generation scheme that uses an adaptive Cascade-based information reconciliation and privacy amplification. In our scheme, to provide good scalability in terms of the number of nodes, we utilize a combinatorial design of public-private key pairs, which means nodes combine more than one key pair to encrypt and decrypt messages. We also show that it provides controllable resilience when malicious nodes compromise a limited number of nodes before key revocation and renewal.
Shared key generation between two users to exploit the randomness of wireless channels as a source of secret key bits extraction has become an attractive alternative to ensure security in a mobile environment. In this paper, we evaluate the performance of key extraction scheme using measurement results of Received Signal Strength (RSS) on several variations of settings and types of movement. We add the moving average method before the quantization process so our scheme becomes more adaptive to the low variation of RSS, and the use of modified Level Crossing Algorithm to reduce Key Disagreement Rate (KDR) due to half-duplex mode, device limitation, and different types of devices. The results show that our proposed schemes, compared with the existing scheme produce bit stream with the highest entropy, a significant decrease of KDR and passed randomness test from NIST statistical suite.
Securing wireless communication remains challenging in dynamic mobile environments due to the shared nature of wireless medium and lacking of fixed key management infrastructures. Generating secret keys using physical layer information thus has drawn much attention to complement traditional cryptographic-based methods. Although recent work has demonstrated that Received Signal Strength (RSS) based secret key extraction is practical, existing RSS-based key generation techniques are largely limited in the rate they generate secret bits and are mainly applicable to mobile wireless networks. In this paper, we show that exploiting the channel response from multiple Orthogonal Frequency-Division Multiplexing (OFDM) subcarriers can provide fine-grained channel information and achieve higher bit generation rate for both static and mobile cases in real-world scenarios. We further develop a Channel Gain Complement (CGC) assisted secret key extraction scheme to cope with channel non-reciprocity encountered in practice. Our extensive experiments using WiFi networks in both indoor as well as outdoor environments demonstrate that our approach can achieve significantly faster secret bit generation rate at 60 ~ 90bit/packet, and is resilient to malicious attacks identified to be harmful to RSS-based techniques including predictable channel attack and stalking attack.
Generating a secret key between two parties by extracting the shared randomness in the wireless fading channel is an emerging area of research. Previous works focus mainly on single-antenna systems. Multiple-antenna devices have the potential to provide more randomness for key generation than single-antenna ones. However, the performance of key generation using multiple-antenna devices in a real environment remains unknown. Different from the previous theoretical work on multiple-antenna key generation, we propose and implement a shared secret key generation protocol, Multiple-Antenna KEy generator (MAKE) using off-the-shelf 802.11n multiple-antenna devices. We also conduct extensive experiments and analysis in real indoor and outdoor mobile environments. Using the shared randomness extracted from measured Received Signal Strength Indicator (RSSI) to generate keys, our experimental results show that using laptops with three antennas, MAKE can increase the bit generation rate by more than four times over single-antenna systems. Our experiments validate the effectiveness of using multi-level quantization when there is enough mutual information in the channel. Our results also show the trade-off between bit generation rate and bit agreement ratio when using multi-level quantization. We further find that even if an eavesdropper has multiple antennas, she cannot gain much more information about the legitimate channel.