Krzysztof Piotrowski

How public key cryptography influences wireless sensor node lifetime

In this paper we try to estimate the real influence of public key cryptography (PKC) to the lifetime of a sensor node in wireless sensor networks. We investigate four types of nodes; MICA2DOT, MICA2, MICAz and TelosB. For all these nodes we estimate the power consumption for most common RSA and ECC operations, i.e., signature generation and verification as well as key exchange mechanisms. We also estimate the power consumed by the transmission of their results. Our results show that the application of strong cryptography is feasible. Even for the most constrained node performing the ECC-160 signature once every 10 minutes increases the duty cycle only by about 0.5 per cent, i.e., the influence to the lifetime is not significant. Nevertheless, the public key cryptography shall be used with care.

tinyDSM: A highly reliable cooperative data storage for Wireless Sensor Networks

The advantage of a Wireless Sensor Network (WSN) compared to a centric approach is the distribution of sensing suites. However, in order for such a system of distributed resources to work in a reliable and effective way a smart cooperation between nodes is needed. In this paper we propose a middleware approach for a highly reliable data storage that helps to assure data availability despite the well known WSN resource problems and disappearing or inactive nodes by providing a reasonable data redundancy in the system. Such a solution helps to ease the design and optimization of the data exchange between nodes as well. Our solution is configurable in order to satisfy the needs of the application on top regarding performance/requirements trade-off. The options specify the quantity and quality of the data replication. Additional features like event mechanism that monitors the data and the possibility to issue database like queries increase the applicability of our middleware. In this paper we focus on the evaluation of its capabilities regarding reliability, the consistency of replicates and the costs of the data management. The simulation results for a reasonable set-up show that the CPU load caused by the data replication is low (below 3 percent) and the average inconsistency time is as small as about 0,06 seconds for a single hop and about 0,15 seconds for a two hops replication area. There is still room for improvements, but a clear definition of problems helps to find ways to cope with them in order to achieve the chosen goals.

Public key cryptography empowered smart dust is affordable

Public Key Cryptography (PKC), although very beneficial for key distribution, authentication and other related issues, was for a long time considered as too expensive for small, battery-powered and resource-constrained devices. In the recent years, first research groups started to cope with the challenges applying PKC in such environments. One of the results is that Elliptic Curve Cryptography (ECC) fits here perfectly, providing the level of security RSA does, but with much shorter keys. In this paper, we evaluate the power consumption induced by various PKC approaches including calculation and transmission costs. Our results clearly show that hardware accelerators significantly reduce the energy consumption and prolong lifetime of sensor nodes. Our solution for 163 bit ECC needs only 1.02 mm² cell area in a 0.25 µm technology and only 12.8 µWs per point multiplication. Due to its small size it can be manufactured for about 0.05 USD in mass production.

On Concealed Data Aggregation for WSNs

In this paper we discuss algorithms that allow the concealed data aggregation (CDA) in wireless sensor networks. We describe and evaluate three algorithms that were reported to suit to the WSN scenario. As result of the evaluation, where we emphasize the awareness to potential attack scenarios, we present a brief overview of strengths and weaknesses of the algorithms. Since no algorithm provides all desirable goals, we propose two approaches to cope with the problems. The first is the successive combination of two algorithms. It increases security, while the additional efforts can be minimized by carefully selected parameters. For the second approach we face specific weaknesses and engineer mechanisms that solve the particular issues. With the considered homomorphic message authentication code and a discussion of the id-issue we exemplary evaluate the two biggest issues of the very promising CMT algorithm. I. MOTIVATION

Body area network for first responders: a case study

In this paper we present a case study for a design of a reliable body area network (BAN) for monitoring fire fighter rescue teams according to the requirements defined by the Berlin fire brigades. This case study considers all layers of the system, starting from the hardware, going through the operating system and data handling middleware, ending at the application layer. The main parts of the proposed solution are the tinyDSM middleware and a new prototyping hardware platform for wireless sensor nodes--IHPNode. The resulting BAN shall be a part of a larger system, where the BANs are connected via an additional multi-hop network to the control centre. Even if this connection fails, the BAN is able to take autonomous decisions. This system is developed within the FeuerWhere project.

A cross-layer approach for data replication and gathering in decentralized long-living wireless sensor networks

Realizing highly reliable wireless sensor networks with a long lifetime is a challenging task. A long lifetime is normally achieved by low duty cycles and rare activity. High reliability requires the replication of data to cope with dying nodes, network fragmentation, etc. These problems become even harder to tackle in networks with no wired sink (decentralized networks), which can synchronize the nodes and store data. We thoroughly investigated the challenges and present a reasonable approach, which adopts cross-layer rendezvous and data dissemination schemes. Our protocol can achieve very good results for lifetime, efficient replication handling and data gathering in decentralized sensor networks. Off-the-shelf sensor nodes based on our approach offer a lifetime of two years. However, our simulation results reveal that very long sleep phases may lead to increased power consumption, which is not expected.

In-network-aggregation as case study for a support tool reducing the complexity of designing secure wireless sensor networks

This paper shows how complex security-related design decisions in wireless sensor networks can be made less difficult with a proposed supporting tool. As case study in this paper we focus on in-network-aggregation which is a promising option to reduce network effort. We introduce several algorithms for concealed data aggregation, each with its own benefits and drawbacks concerning security issues but also with respect to code size, processing overhead etc. Selecting the optimal combination requires in-depth knowledge of programming resource constrained devices, protocols for those devices, and last but not least significant background in security. Our proposed configuration tool - named configKIT - has been designed to cope with such complexity. This paper presents how configKIT works, how it will be set up, and how it can be applied in practice. The pre-compiler assessment process considers memory, energy and security parameters and provides reliable application-dependent configurations to the developer before a single line of code is written. The approach can reduce development time significantly and enables even complex and sophisticated security algorithms to a broader public.

Distributed Shared Memory as an Approach for Integrating WSNs and Cloud Computing

In this paper we discuss the idea of combining wireless sensor networks and cloud computing starting with a state of the art analysis of existing approaches in this field. As result of the analysis we propose to reflect a real wireless sensor network by virtual sensors in the cloud. The main idea is to replicate data stored on the real sensor nodes also in the virtual sensors, without explicit triggering such updates from the application. We provide a short overview of the resulting architecture before explaining mechanisms to realize it. The means to ensure a certain level of consistency between the real WSN and the virtual sensors in the cloud is distributed shared memory. In order to realize DSM in WSNs we have developed a middleware named tinyDSM which is shortly introduced here and which provides means for replicating sensor data and ensuring the consistency of the replicates. Even though tinyDSM is a pretty good vehicle to realize our idea there are some open issues that need to be addressed when realizing such an architecture. We discuss these challenges in an abstract way to ensure clear separation between the idea and its specific realization.

Flexible hardware reduction for elliptic curve cryptography in GF(2 m )

This paper discuss two ways to provide flexible hardware support for the reduction step in elliptic curve cryptography in binary fields (GF(2m)). In the first approach the authors are using several dedicated reduction units within a single multiplier. The measurement results show that this simple approach leads to an additional area consumption of less than 10% compared to a dedicated design without performance penalties. In the second approach any elliptic curve cryptography up to a predefined maximal length can be supported. Here the authors take advantage of the features of commonly used reduction polynomials. The results show a significant area penalty compared to dedicated designs. However, the authors achieve flexibility and the performance is still significantly better than those of known ECC hardware accelerator approaches with similar flexibility or even software implementations

Symbiosis of a Lightweight ECC Security and Distributed Shared Memory Middleware in Wireless Sensor Networks

In this paper we present our work on a combination of two approaches for wireless sensor networks (WSNs), to provide a self contained, reliable and secure shared memory middleware with security management. The shortECC is a lightweight and short key cryptosystem that requires management layer for its parameters and tinyDSM is a middleware that provides a shared memory abstraction. The combination of these two approaches is a kind of symbiosis, where the tinyDSM is used by the shortECC for the management and distribution of its parameters within a trusted group while using the security means provided by the latter. This symbiosis ensures secured tinyDSM data exchange and reliable management of the shortECC parameters at almost no additional cost and is competitive when compared to AES or standard elliptic curves cryptography.