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Issue No. 05 - May (2013 vol. 12)
ISSN: 1536-1233
pp: 917-930
Sriram Nandha Premnath , University of Utah, Salt Lake City
Suman Jana , University of Utah, Salt Lake City
Jessica Croft , University of Utah, Salt Lake City
Prarthana Lakshmane Gowda , University of Utah, Salt Lake City
Mike Clark , Air Force Research Laboratory and Air Force Institute of Technology
Sneha Kumar Kasera , University of Utah, Salt Lake City
Neal Patwari , University of Utah, Salt Lake City
Srikanth V. Krishnamurthy , University of California, Riverside, Riverside
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 1) 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, 2) an adversary can cause predictable key generation in these static environments, and 3) 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.
Privacy, Wireless communication, Entropy, Quantization, Bit rate, Educational institutions, key generation, Wireless networks, multipath fading, physical layer, cryptography

M. Clark et al., "Secret Key Extraction from Wireless Signal Strength in Real Environments," in IEEE Transactions on Mobile Computing, vol. 12, no. , pp. 917-930, 2013.
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