Cooperative jam Technique to Increase Physical-layer Security in CWSN Alvaro Araujo, Javier Blesa, Elena Romero, Octavio Nieto-Taladriz E.T.S.I. Telecomunicacion Electronic Engineering Department Universidad Politecnica de Madrid Madrid, Spain {araujo,jblesa,elena,nieto}@die.upm.es Abstract— This paper considers the problem of secure communication in Wireless Sensor Networks in the presence of non-colluding passive eavesdroppers. Cognitive networks capabilities such as spectrum sensing, share information and collaboration to optimize the communications can be used to avoid attacks. A collaborative jamming technique is proposed to increase Cognitive Wireless Sensor Networks security and a counter measurement against eavesdropped attacks. Three types of scenarios are defined: attacker location known, attacker location unknown, and attacker and relay co-location. Each new scenario adds a difficulty to the countermeasure to the previous one. Simulations show as Secrecy Outage Probability decreases until 10% with a standard number of relay nodes in the network. As a result, cooperative jamming strategies are seen to be highly effective for increasing the secrecy in Wireless Sensors Networks. Keywords-WSN; cognitive; jamming; collaborative; security I. INTRODUCTION Wireless Sensor Networks (WSN) is one of the fastest growing sectors in recent years. The unlicensed Industrial, Scientific and Medical (ISM) spectrum bands, used by these networks, are becoming overcrowded. The cognitive paradigm has appeared to solve spectrum scarcity, interference and reliable connections problems. Cognitive Wireless Sensor Networks (CWSN) are based on the cycle sensing spectrum monitoring, analyzing for environment characterization, reasoning to chose the best communication strategy, and sending to provide adaptation and collaboration. Cooperation between devices regarding information sharing and taking decisions allows better spectrum use, lower energy consumption and better data reliability. CWSN are used in systems with critical data (telecare monitoring, military scenarios) and critical applications (safety home system, infrastructure protection, etc.). Hence, security is a fundamental challenge to face. Cognitive nature of the system introduces an entire new suite of threats and attacks that are not easily mitigate. The broadcast characteristic of the wireless medium makes difficult to shield transmitted signals form unintended recipients. Security in wireless data transmission has traditionally been developed using cryptographic techniques at the network layer. The main drawback of this approach when deployed to WSN consists in limited resources, which cannot support the execution of complicated encryption algorithms, resulting in shorter keys that are easier to discover. WSN nodes can also be captured and attackers use reverse-engineered and become an instrument for mounting counterattacks. Physical-layer security becomes a very interesting approach in the past few years [1]. The main idea behind physical-layer security is to limit the amount of information that can be extracted at the ‘bit’ level by unauthorized receivers with the exploitation of all available Channel State Information (CSI). The fundamental problem in WSN is the difficulty to obtain a full CSI. Cognitive paradigm allows the spectrum monitoring and provides this information to the network. In this paper, a selective jam technique to increase physical- layer security in CWSN using cognitive capabilities is presented. This technique can operate independently of the higher layers to complement security requirements. The organization of this paper is as follows. In Section II, works in physical-layer security for WSN are reviewed. In Section III, we formulate the technique description. Section IV provides its evaluation. Finally, the collusions are drawn in Section V. II. PHYSICAL-LAYER SECURITY APPROACHES In this section, we introduce schemes that could be used to achieve physical layer security against different attacks in WSN. In recent years, the main issues of secure channel capacity have drawn much attention in the information theory community. Most of the works are focused in schemes to obtain the secrecy capacity with different CSI approaches. Barros and Rodrigues in [2] developed a secure communication protocol to ensure wireless information-theoretic security based on: common randomness via opportunistic transmission, message reconciliation, common key generation via privacy amplification and, finally, message protection with a secret key. It was shown that the protocol is effective in secure key renewal even the presence of imperfect CSI. Other methods have been proposed to avoid attacks based on exploitation of channel characteristics. The Radio Frequency (RF) fingerprinting system implemented by [3] consists of multiple sensor system that captures and extracts RF 11 Copyright (c) IARIA, 2012. ISBN: 978-1-61208-197-7 COCORA 2012 : The Second International Conference on Advances in Cognitive Radio