Joachim Wilke

Realistic simulation of energy consumption in wireless sensor networks

In this paper we analyze whether energy consumption in a wireless sensor network (WSN) can be evaluated realistically and accurately using the Avrora simulation tool. For this purpose, results from a reference experiment using SANDbed, a WSN testbed with focus on energy measurements, and Avrora, a wireless sensor network simulation tool, are compared. In this experiment, we found a difference in total energy consumption up to 20% between simulation and reality. The analysis revealed several issues that influenced the accuracy of Avrora simulations. We thus adapted Avrora for dealing with the identified issues. A concluding evaluation shows that the improved Avrora+ reduces the difference between simulation and testbed to <5%.

Energy evaluations in wireless sensor networks: a reality check

The development of energy-efficient applications and protocols is one of the most important issues in Wireless Sensor Networks (WSN). However, most publications up to now avoid time consuming realistic energy evaluations and oversimplify their evaluation with regard to energy-efficiency. This work aims at lowering the barrier for realistic energy evaluations. We focus on a generic application that simply transmits one packet using TinyOS Low Power Listening (LPL), which we evaluate using the WSN testbed SANDbed. Our results disprove some intuitive expectations. For example, we show that transmitting packets with a large payload can be cheaper in terms of energy consumption than a small payload. As packet transmission is part of almost any WSN application, the results shown are important to many WSN protocol evaluations. As an addition, we contribute our lessons learned by discussing the most important challenges and pitfalls we faced during our evaluation.

A security-energy trade-off for authentic aggregation in sensor networks

To reduce energy consumption, aggregation takes place in a wireless sensor network. All measured data is collected and preprocessed multiple times on its way towards a data sink, e.g., a base station. However, aggregation implies new challenges to security: as the sink Anally receives aggregated data, it is difficult to verify not only the aggregates correctness, but also the origin of the data the aggregate was computed from. In the presence of an attacker in the network, data transmissions and aggregation could have maliciously been modified. Yet, it turns out that in-network aggregation and data authenticity are contradictory communication properties. This research examines the possibility of finding a trade-off between security (authenticity) and energy-savings (aggregation). If the user is willing to accept datas authenticity with ples100% probability, he can still save large amounts of energy compared to authentic communication without aggregation.

Evaluating the energy-efficiency of key exchange protocols in wirelesssensor networks

The evaluation of the energy-efficiency of applications and protocols is one of the most important issues in Wireless Sensor Networks (WSN). However, this is a time consuming and challenging task. Therefore, a realistic energy-efficiency evaluation is often neglected or oversimplified by using simple theoretical models or unsuited simulation tools. In this work, we evaluate the energy-efficiency of two specific key exchange protocols, an Elliptic Curve Diffie-Hellman with authentication (ECDH-ECDSA) and a Kerberos based approach, while using different duty-cycling MAC layer protocols. In our evaluation, we compare the results from a theoretical model with simulation results using the AVRORA+ simulation tool and real-world measurements in our WSN testbed SANDbed. Using three MAC layer protocols, TinyOS built in Low-Power-Listening as well as S-MAC and standard 802.15.4, we show that there are several important cross-layer effects that should be considered when performing an energy-efficiency evaluation. Furthermore, we argue, that there are several evaluation metrics like the absolute energy consumption per key exchange or one key exchange per measured time interval.

ESAWN-NR: Authentic aggregation and non-repudiation in wireless sensor networks

This demonstration shows ESAWN-NR in action, a protocol for authentic, yet efficient data aggregation in presence of malicious, compromised sensor nodes. ESAWN-NR does not only achieve authenticity of data aggregates, but also allows to prove forged aggregates coming from specific nodes. This allows easy exclusion of such nodes from the network.

Evaluating energy-efficiency of hardware-based security mechanisms

Security in Wireless Sensor Networks (WSNs) is an omnipresent topic. In many application scenarios, like the surveillance of critical areas or infrastructures, security mechanisms have to be used to build reliable and secure applications. Up to now, most of the used cryptographic algorithms have been implemented in software despite the resource constraints in terms of processing power, memory and energy. In the past few years, the usage of special hardware accelerated security modules has been proposed as a viable alternative to software implementations. However, the energy-efficiency has not yet been evaluated in-depth. In this paper, we analyze the VaultIC420 security module and present an evaluation of its energy-efficiency. We compare the performance and energy-efficiency of the hardware module to common software implementations like TinyECC. For the energy measurements, we use IRIS sensor nodes in the SANDbed testbed at the Karlsruhe Institute of Technology. Our evaluation shows, that the VaultIC420 can save up to 76% of energy using different MAC layer protocols. It also shows, that the current draw of the VaultIC420 requires a duty-cycling mechanisms to achieve any savings compared to the software implementation.

Authentic query dissemination and data aggregation in WSN

In a public wireless sensor network (WSN), the presence of adversaries that can completely take over some sensor nodes must be taken into account. The adversary may try to use the compromised nodes to inject his own queries or to influence results of legitimate queries, when they are propagated to the networks sink during data concast. Because of the commonly used paradigm of in-network processing, a compromised node can manipulate all passing data easily. Hence, the authenticity of both, query and result, must be verified. However, providing authenticity needs additional effort, which increases energy-consumption. We present AQF+ESAWN, the (to our knowledge) first attempt to provide an integrated solution for authentic query processing and data concast in WSNs in an energy-efficient, configurable way. Before describing the benefits of this demonstration, we shortly sketch the two protocols AQF and ESAWN and the energy-authenticity trade-off provided.

Energy-efficiency of concast communication in Wireless Sensor Networks

In monitoring scenarios, Wireless Sensor Networks commonly transmit measurements from a large number of sensor nodes to a central data sink. This communication pattern is known as concast. Different approaches have been proposed to improve the energy-efficiency of concast and thus the lifetime of the WSN. However, energy-efficiency evaluations that are close to reality are missing. This paper systematically analyzes the influence of aggregation strategies, tree topologies, and different MAC protocols on the energy-efficiency of concast communication. We implement a sample concast application and analyze it using the AVRORA + simulator to gain realistic evaluation results. Our results disproof some common assumptions. We show that aggregation improves energy-efficiency only in a few cases and can even degrade it. Instead, MAC protocol and parametrization have a higher impact on energy-efficiency.

A Framework for Probabilistic, Authentic Aggregation in Wireless Sensor Networks

ABSTRACT Wireless sensor networks suffer from limited resources, in particular finite energy supply. A common way to save energy is reducing radio transmissions by using in-network data aggregation, which is very sensitive to non-cooperative nodes, e.g., nodes that have been compromised by an attacker. Usually, security to such attacks can only be achieved by spending considerably more energy. In this paper, we present the ESAWN framework, a highly customizable protocol for secure in-network data aggregation. The main contribution of ESAWN is providing gracefully degrading security guarantees, in particular dataauthenticity. Instead of providing ‘full’ authenticity, we only assure an aggregate to be authentic with a given probability. This is done by propagating aggregates on redundant paths, allowing other nodes to check correctness. Hence, a user can trade-off security against energy in a very fine-grained manner. We present both analytical and MICA2-based simulation results, showing the practicality of our approach. For example, with 10% compromised nodes, ESAWN saves, up to 70% energy while degrading authenticity by 5%.

Evaluating the energy-efficiency of the Rich Uncle key exchange protocol in WSNs

This paper evaluates the energy consumption of three key exchange protocols Rich Uncle, (EC)DH-(EC)DSA and Kerberos. It aims at determining which protocol can exchange keys between two sensor nodes in the most energy-efficient way. To realistically compare the energy consumption, the protocols are implemented in TinyOS on the MICAz platform and simulated using the Avrora+ simulator. The key exchange protocols are evaluated in combination with four common duty-cycling MAC protocols. We show, that the Kerberos protocol is the key exchange protocol with the least overall energy consumption per key exchange, mostly due to the extremely cheap cryptographic operations. When compared with the ECDH-ECDSA key exchange protocol, this outweighs the additional message overhead needed for communication with the trusted third party in Kerberos. Rich Uncle fails to beat ECDH-ECDSA, even after off-loading the more expensive cryptographic operations to the Rich Uncle super nodes. Furthermore, we show that there are cross-layer effects caused by the MAC protocols that highly influence the overall energy consumption of the key exchange protocols.