INTEGRITY & AUTHENTICITY IN SENSOR NETWORKS Nikos Komninos, Ioannis Kolokouris, and Nikos Zarokostas Athens Information Technology GR-190 02, Peania (Attiki), Greece ABSTRACT Sensor networks consist of cheap, smart devices, with multiple onboard sensors, networked through wireless links and deployed in large numbers. In critical applications it is essential to secure the vulnerable wireless communication in order to avoid intrusions. In this paper, an efficient authentication and integrity mechanism for sensor networks is proposed. The limited resources of motes and the peculiarities of the wireless communication channel have driven us to the proposal of a low weight hash function, which is used in combination with a key to produce MACs. This key, which is shared among motes and base station, is frequently changed. The key is exchanged once, during the deployment of the sensor network, and specific steps need to be followed to secure the communication among motes and base station. INTRODUCTION Sensor networks provide us with solutions for monitoring and tracking events within large areas. Thousands of tiny motes are spread over to cover an area with their sensing capabilities. Every single mote can be programmed to perform simple tasks of sensing and processing, but their great usefulness comes from their ability to communicate and cooperate towards a common purpose. So, a vital task of motes is the message exchange, firstly among the motes and secondly between mote and base station so as to gather valuable data for further processing and interpretation. In sensor networks, the communication channel is wireless and the environment where motes are deployed may sometimes be hostile (e.g. military applications). Therefore, mechanisms that ensure integrity, authenticity, and confidentiality of data should be applied. These security issues are well studied and solved for wired and wireless computer networks. Plenty of algorithms have been proposed and tested over the years to address integrity, authenticity, and confidentiality challenges. However, because of the limited power and processing capabilities of sensor motes, these algorithms have to be re-designed or new ones have to be proposed to cope with the restricted resources. In this paper we propose a mechanism that provides mote authentication and data integrity for the communication among motes and base station. Our mechanism uses a low weight hash function that we have designed for a specific communication model. Following this introduction, the paper is organized as follows. Section II presents work related to the issue of secure communication in sensor networks. Section III describes the proposed mechanism and section IV provides a security analysis of our proposal, in order to evaluate its effectiveness. Finally, section V analyses the experimental results and in section VI we reach to our conclusion. RELATED WORK Sensor networks constitute a novel technology that has recently started evolving. So far, integrity and authenticity in sensor network is achieved by TinySec, SNEP and TinyHash mechanisms. TinySec [1] is a carefully designed and tested link layer security architecture proposed and implemented by Karlof, Sastry and Wagner at Berkeley University, US. It utilizes the Skipjack [2] (or Rivest Code version 5 – RC5 [3]) block cipher in Cipher Block Chaining (CBC) mode for encryption and CBC-MAC to achieve message integrity and authentication, utilizing the already implemented block cipher. TinySec always authenticates messages, but encryption is optional. Message confidentiality is only necessary when there is something to keep secret. Moreover, protection against replay attack is not provided as it is considered more suitable to be placed in the application layer. TinySec comes with TinyOS, an operating system for sensor motes created also at Berkeley. SNEP [4] is an early first step on this field, specifically targeting sensor networks. It is based around a single block cipher that is used for authentication, confidentiality and random number generation. However, SNEP was neither fully implemented nor fully specified. TinyHash [5] is using HMAC [6] with Secure Hash Algorithm (SHA-1) for message integrity and authentication. Its design is highly influenced by TinySec, except it uses a hash function instead of the block cipher technique. However, the necessity of the design of a light weight hash algorithm is stated in the conclusions. PROPOSED INTEGRITY & AUTHENTICITY MECHANISM IN SENSOR NETWORKS Sensor network is a heterogeneous system combining motes of different types. It consists of hundreds or thousands of low- cost wireless motes, deployed to monitor the environment and report events of interest. Some of the applications that are expected to be early adopters of wireless sensor networks are asset and warehouse management, automotive, building monitoring and control, environmental monitoring, health care, military and surveillance. However, due to the wireless medium, sensor networks are susceptible to various types of security threats such as eavesdropping, message replay, and fabrication of messages. These threats can be avoided by