Karine Altisen

SR3: Secure Resilient Reputation-based Routing

We propose SR3, a secure and resilient algorithm for convergecast routing in WSNs. SR3 uses lightweight cryptographic primitives to achieve data confidentiality and data packet unforgeability. SR3 has a security proven by formal tool. We made simulations to show the resiliency of SR3 against various scenarios, where we mixed selective forwarding, blackhole, wormhole, and Sybil attacks. We compared our solution to several routing algorithms of the literature. Our results show that the resiliency accomplished by SR3 is drastically better than the one achieved by those protocols, especially when the network is sparse. Moreover, unlike previous solutions, SR3 self-adapts after compromised nodes suddenly change their behavior.

Analysis of random walks using tabu lists

A tabu random walk on a graph is a partially self-avoiding random walk which uses a bounded memory to avoid cycles. This memory is called a tabu list and contains vertices already visited by the walker. The size of the tabu list being bounded, the way vertices are inserted and removed from the list, called here an update rule, has an important impact on the performance of the walk, namely the mean hitting time between two given vertices. n nWe define a large class of tabu random walks, characterized by their update rules. We enunciate a necessary and sufficient condition on these update rules that ensures the finiteness of the mean hitting time of their associated walk on every finite and connected graph. According to the memory allocated to the tabu list, we characterize the update rules which yield smallest mean hitting times on a large class of graphs. Finally, we compare the performances of three collections of classical update rules according to the size of their associated tabu list.

SR3: secure resilient reputation-based routing

AbstractIn this paper, we propose SR3 (which means secure resilient reputation-based routing), a secure and resilient algorithm for convergecast routing in wireless sensor networks. SR3 uses lightweight cryptographic primitives to achieve data confidentiality and unforgeability. Security of SR3 has been proven formally using two verification tools: CryptoVerif and Scyther. We made simulations to show the resiliency of SR3 against various scenarios, where we mixed selective forwarding, blackhole, wormhole, and Sybil attacks. We compared our solution to several routing algorithms of the literature. Our results show that the resiliency accomplished by SR3 is drastically better than the one achieved by those protocols, especially when the network is sparse. Moreover, unlike previous solutions, SR3 self-adapts after compromised nodes suddenly change their behavior.n

Self-stabilizing Leader Election in Polynomial Steps

We propose a silent self-stabilizing leader election algorithm for bidirectional connected identified networks of arbitrary topology. This algorithm is written in the locally shared memory model. It assumes the distributed unfair daemon, the most general scheduling hypothesis of the model. Our algorithm requires no global knowledge on the network (such as an upper bound on the diameter or the number of processes, for example). We show that its stabilization time is in Θ(n^3) steps in the worst case, where n is the number of processes. Its memory requirement is asymptotically optimal, i.e., Θ(log n) bits per processes. Its round complexity is of the same order of magnitude — i.e., Θ(n) rounds — as the best existing algorithm (Datta et al, 2011) designed with similar settings. To the best of our knowledge, this is the first self-stabilizing leader election algorithm for arbitrary identified networks thatis proven to achieve a stabilization time polynomial in steps. By contrast, we show that the previous best existing algorithm designed with similar settings (Datta et al, 2011) stabilizes in a non polynomial number of steps in the worst case.

On Probabilistic Snap-Stabilization

In this paper, we introduce probabilistic snap-stabilization. We relax the definition of deterministic snap-stabilization without compromising its safety guarantees. In an unsafe environment, a probabilistically snap-stabilizing algorithm satisfies its safety property immediately after the last fault; whereas its liveness property is only ensured with probability 1. n nWe show that probabilistic snap-stabilization is more expressive than its deterministic counterpart. Indeed, we propose two probabilistic snap-stabilizing algorithms for a problem having no deterministic snap- or self-stabilizing solution: guaranteed service leader election in arbitrary anonymous networks. This problem consists in computing a correct answer to each process that initiates the question Am I the leader of the network?, i.e., 1 processes always computed the same answer to that question and 2 exactly one process computes the answer true. n nOur solutions being probabilistically snap-stabilizing, the answers are only delivered within an almost surely finite time; however any delivered answer is correct, regardless the arbitrary initial configuration and provided the question has been properly started.

Comparison of mean hitting times for a degree-biased random walk

Consider the random walk on graphs such that, at each step, the next visited vertex is a neighbor of the current vertex, chosen with probability proportional to the inverse of the square root of its degree. On one hand, for every graph with n vertices, the maximal mean hitting time for this degree-biased random walk is asymptotically dominated by n^2. On the other hand, the maximal mean hitting time for the simple random walk is asymptotically dominated by n^3. Yet, in this article, we exhibit for each positive integer n: *A graph of size n with maximal mean hitting time strictly smaller for the simple random walk than for the degree-biased one. *A graph of size n with mean hitting time of a so called root vertex strictly smaller for the simple random walk than for the degree-biased one.

Collision prevention in distributed 6TiSCH networks

The IEEE802.15.4e standard for Iow power wireless sensor networks defines a new mode called Time Slotted Channel Hopping (TSCH) as Medium Access Control (MAC). TSCH allows highly efficient deterministic time-frequency schedules that are built and maintained by the 6TiSCH operation sublayer (6top). In this paper, we propose a solution to limit the allocation of identical cells to co-located pair of nodes by distributed TSCH scheduling algorithms. It consists of making nodes able to overhear past cell negotiations exchanged in shared cells by their neighbors and prevent the nodes from reusing already assigned cells in future allocations. Our mechanism has been tested through simulations that show a significant improvement with respect to random scheduling algorithms.

Leader Election in Asymmetric Labeled Unidirectional Rings

We study (deterministic) leader election in unidirectional rings of homonym processes that have no a priori knowledge on the number of processes. In this context, we show that there is no algorithm that solves process-terminating leader election for the class of asymmetric labeled rings. In particular, there is no process-terminating leader election algorithm in rings in which at least one label is unique. However, we show that process-terminating leader election is possible for the subclass of asymmetric rings, where multiplicity is bounded. We confirm this positive results by proposing two algorithms, which achieve the classical trade-off between time and space.

Concurrency in snap-stabilizing local resource allocation

In distributed systems, resource allocation consists in managing fair access of a large number of processes to a typically small number of reusable resources. As soon as the number of available resources is greater than one, the efficiency in concurrent accesses becomes an important issue, as a crucial goal is to maximize the utilization rate of resources. In this paper, we tackle the concurrency issue in resource allocation problems. We first characterize the maximal level of concurrency we can obtain in such problems by proposing the notion of maximal concurrency. Then, we focus on Local Resource Allocation problems (LRA). Our results are both negative and positive. On the negative side, we show that there is a wide class of instances of LRA for which it is impossible to obtain maximal concurrency without compromising the fairness. On the positive side, we propose a snap-stabilizing LRA algorithm which achieves a high (but not maximal) level of concurrency, called here strong concurrency. We define several notions of concurrency, including maximal concurrency which is the maximal level of concurrency achievable in a resource allocation problem.We show that maximal concurrency cannot always be achieved in Local Resource Allocation (LRA) problems.We propose a snap-stabilizing LRA algorithm achieving a high (but not maximal) level of concurrency.

Leader Election in Rings with Bounded Multiplicity (Short Paper)

We study leader election in unidirectional rings of homonym processes that have no a priori knowledge on the number of processes. We show that message-terminating leader election is impossible for any class of rings (mathcal K_k) with bounded multiplicity (k ge 2). However, we show that process-terminating leader election is possible in the sub-class (mathcal U^* cap mathcal K_k), where (mathcal U^*) is the class of rings which contain a process with a unique label.