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Low-cost standard signatures in wireless sensor networks: a case for reviving pre-computation techniques?

Effective pre-computation techniques have been proposed almost 15 years ago for trimming the cost of modular exponentiations at the basis of several standard signature and key management schemes, such as the (Elliptic Curve) Digital Signature Algorithm or Diffie-Hellman key exchange. Despite their promises, the actual application of such techniques in the wireless sensor security arena has been apparently overlooked, and most of the research effort has rather focused on the identification of alternative lightweight constructions. However, modern sensor are equipped with relatively large flash memories which make memory consumption a less critical requirement, and emerging energy harvesting technologies provide occasional energy peaks which could be exploited for anticipating otherwise costly computational tasks. These trends push for a reconsideration of pre-computation techniques, which are explored in this paper as follows: (1) we further optimize prior pre-computation techniques by exploiting more recent results on Cayley graph expanders, (2) we implement an ECDSA scheme relying on pre-computations over two different wireless sensor node platforms (TelosB and MICA2), and (3) we experimentally assess the relevant performance and energy costs. In the traditional scenario of wireless sensor networks without energy harvesting, our prototype ECDSA implementation, despite still not fully optimized, outperforms prior work by almost 50%, and achieves an efficiency superior to NTRU signatures, natural candidates for low-power devices. Finally, (4) we quantitatively discuss ways to exploit harvested energy peaks to further improve efficiency

AGREE: exploiting energy harvesting to support data-centric access control in WSNs

This work is motivated by a general question: can energy harvesting capabilities embedded in modern sensor nodes be exploited so as to support security mechanisms which otherwise would be too demanding and hardly viable? More specifically, in this work we focus on the support of extremely powerful, but complex, fine-grained data-centric access control mechanisms based on multi-authority Ciphertext Policy Attribute Based Encryption (CP-ABE). By integrating access control policies into the (encrypted) data, such mechanisms do not require any server-based access control infrastructure and are thus highly desirable in many wireless sensor network scenarios. However, as concretely shown by a proof-of-concept implementation first carried out in this paper on TelosB and MicaZ motes, computational complexity and energy toll of state-of-the-art multi-authority CP-ABE schemes is still critical. We thus show how to mitigate the relatively large energy consumption of the CP-ABE cryptographic operations by proposing AGREE (Access control for GREEn wireless sensor networks), a framework that exploits energy harvesting opportunities to pre-compute and cache suitably chosen CP-ABE-encrypted keys, so as to minimize the need to perform CP-ABE encryptions when no energy from harvesting is available. We assess the performance of AGREE by means of simulation and actual implementation, validating its operation with real-world energy-harvesting traces collected indoors by TelosB motes equipped with photovoltaic cells, as well as public available traces of radiant light energy. Our results show that complex security mechanisms may become significantly less demanding when implemented so as to take advantage of energy harvesting opportunities. © 2013 Elsevier B.V. All rights reserved