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Abstract-Bluetooth has found widespread adoption in phones, wireless headsets, stethoscopes, glucose monitors, and oximeters for communication of, at times, very critical information. However, the link keys and encryption keys in Bluetooth are ultimately generated from a short 4 digit PIN, which can be cracked off-line. We develop an alternative for secure communication between Bluetooth devices using the symmetric wireless channel characteristics. Existing approaches to secret key extraction primarily use measurements from a fixed, single channel (e.g., a 20 MHz WiFi channel); however in the presence of heavy WiFi traffic, the packet exchange rate in such approaches can reduce as much as 200×. We build and evaluate a new method, which is robust to heavy WiFi traffic, using a very wide bandwidth (B 20 MHz) in conjunction with random frequency hopping. We implement our secret key extraction on two Google Nexus One smartphones and conduct numerous experiments in indoor-hallway and outdoor settings. Using extensive real-world measurements, we show that outdoor settings are best suited for secret key extraction using Bluetooth. We also show that even in the absence of heavy WiFi traffic, the performance of secret key generation using Bluetooth is comparable to that of WiFi while using much lower transmit power.

Abstract-Internet of Things (IoT) represents an emerging era of networking that connects a variety of common appliances to one another, as well as with the rest of the Internet, to vastly improve our lives. Despite being significantly resourceconstrained, IoT nodes are expected to participate in numerous computationally-intensive security protocols to overcome threats from the public Internet. Given that IoT nodes (e.g., smart meters) typically exchange tactical data that requires data protection for a short time span of up to a few days, we examine the use of smaller cryptographic key sizes to provide IoT security. We show that small key sizes quite drastically reduce the cryptographic computational processing requirements for IoT nodes. We estimate the cost of breaking public key crypto systems when the adversary is limited by the available resources (i.e., dollar cost) and time (i.e., number of days). We consider Moore's law, as well as More than Moore, and Less than Moore technology growth rates, in conjunction with the capabilities of a real-world key-breaker to calculate the cost estimates. Finally, we also present the trade-off between the processing load for an IoT node versus the desired time span of privacy protection.

Secret key establishment is a fundamental requirement for private communication between two entities. In this article, we propose and evaluate a new approach for secret key extraction where multiple sensors collaborate in exchanging probe packets and collecting channel measurements. Essentially, measurements from multiple channels have a substantially higher differential entropy compared to the measurements from a single channel, thereby resulting in more randomness in the information source for key extraction, and this in turn produces stronger secret keys. We also explore the fundamental trade-off between the quadratic increase in the number of measurements of the channels due to multiple nodes per group versus a linear reduction in the sampling rate and a linear increase in the time gap between bidirectional measurements. To experimentally evaluate collaborative secret key extraction in wireless sensor networks, we first build a simple yet flexible testbed with multiple TelosB sensor nodes. Next, we perform large-scale experiments with different configurations of collaboration. Our experiments show that in comparison to the 1 × 1 configuration, collaboration among sensor nodes significantly increases the secret bit extraction per second, per probe, as well as per millijoule of transmission energy. In addition, we show that the collaborating nodes can improve the performance further when they exploit both space and frequency diversities.