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Simulations have shown multi-armed bandit (MAB) algorithms to be suitable for optimizing channel hopping in IEEE 802.15.4 networks. Thus far, however, there appears to be no practical implementation of this approach, presumably because typical IEEE 802.15.4 nodes lack both floating-point units (FPUs) and big amounts of randomaccess memory (RAM). In this paper, we propose fixed-point arithmetic and implementation shortcuts to circumvent these constraints. We focus on two specific multi-armed bandit (MAB) algorithms, namely slidingwindow upper confidence bound (SW-UCB) and its predecessor discounted UCB (D-UCB). SW-UCB is particularly promising since it requires only tractable fixed-point arithmetic, while yielding high packet delivery ratios (PDRs) according to prior work. D-UCB, on the other hand, additionally opens up an implementation shortcut that saves RAM. Our implementations of SW-UCB and D-UCB are integrated into Contiki-NG, yet can also be used out-of-tree in a simulation environment. We show our SW-UCB (resp. D-UCB) implementation to attain PDRs of 98.6% (resp. 99.2%) under appropriate parameter settings in the context of intra-body communication. Also, we demonstrate D-UCB to incur a moderate RAM, program memory, and processing overhead on CC2538 SoCs, whereas we find SW-UCB too RAM-consuming for these chips. Finally, using Monte Carlo simulations, we show our SW-UCB and D-UCB implementations to perform equally well as floating-point counterparts. IntroductionEarly efforts on applying channel hopping to IEEE 802.15.4 networks followed various goals. Two initial ones were to increase throughput and to lower latencies through the use of additional channels [8,20,22,33]. Further ones were to evade channels that are subject to external interference, destructive fading effects, or jamming attacks [8,32,37]. Lastly, there was also the goal of extending communication range since particular channels may benefit from constructive fading effects [32]. Meanwhile, channel hopping became an integral part of the IEEE 802.15.4 standard [2]. The 2020 version of IEEE 802.15.4 specifies three medium access control (MAC) protocols that support channel hopping, namely coordinated sampled listening (CSL), time-slotted channel hopping (TSCH), and carrier sense multiple access with collision avoidance (CSMA-CA).

6LoWPAN networks are 802.15.4-based wireless sensor networks that seamlessly integrate with IPv6 networks using specially designed protocols. Unfortunately, 6LoWPAN networks are vulnerable to hidden wormholes. To detect and subsequently avoid hidden wormholes, Jain et al. recently proposed two schemes, which exploit the reciprocity of received signal strength indicators (RSSIs). However, threats and attacks can mislead Jain et al.'s schemes into reaching false positives or false negatives. Moreover, their schemes take calibrated RSSIs for granted, which is impractical. In this paper, we propose "Secure Channel REciprocity-based WormholE Detection (SCREWED)", which avoids both false positives and false negatives to a great extend. For this, SCREWED uses channel hopping, randomized transmission powers, message integrity codes, as well as a special replay protection mechanism. Furthermore, SCREWED obviates the need for calibrating RSSIs by using a different channel reciprocity metric. We integrated SCREWED into the link layer of Contiki's 6LoWPAN stack and demonstrate SCREWED's efficacy using TelosB motes.

6LoWPAN is a protocol stack for seamlessly integrating 802.15.4-based wireless sensor networks with IPv6 networks. The security of 6LoWPAN widely depends on the 802.15.4 security sublayer. This sublayer also supports pairwise keys so as to mitigate node compromises. Currently, the establishment of pairwise keys is however unspecified. Moreover, broadcast keys are shared among multiple nodes, which is not compromise resilient. In this paper, we propose two energy-efficient and DoS-resilient 802.15.4 add-ons to fill these gaps: First, a pairwise key establishment scheme, which is adaptable to different 6LoWPAN networks and threat models. Second, an easy-to-implement and compromise-resilient protocol for authenticating broadcast frames. Together, our add-ons contain the effects of node compromises and provide a basis for detecting compromised nodes autonomously. We implemented both add-ons in Contiki and tested them on TelosB motes.