ELPA: A NEW KEY AGREEMENT SCHEME BASED ON LINEAR PREDICTION OF ECG FEATURES FOR WBAN Emna Kalai Zaghouani *† , Abderrazak Jemai ‡ , Adel Benzina * , Rabah Attia * * Laboratory of Electronic Systems and Communication Network, TUNISIA Polytechnic School † TELNET Innovation Labs, Telnet Holding Tunis, Tunisia ‡ Laboratoire LIP2, Facult´ e des Sciences de Tunis, 1060 Belv´ ed` ere Tunis, Tunisie Emna.kalai@telnet-consulting.com, Abderrazak.Jemai@insat.rnu.tn, Adel.Benzina@isd.rnu.tn,Rabah.attia@enit.rnu.tn ABSTRACT In this paper, we propose a novel key agreement scheme called ECG Linear Prediction key Agreement (ELPA) with the properties of plug-n-play and transparency to secure inter-sensor communication in Wireless Body Area Networks (WBANs). ELPA is a new physiological based key agreement scheme allowing two nodes belonging to the same WBAN to agree on a symmetric key from ECG signal features. The paper introduces the use of Linear Prediction Coding (LPC), which has always been used for a compression purpose, in hiding the cryptographic key. In fact we prove that concealing the symmetric key using this tool ensures high security level while keeping low computational complexity and communi- cation overhead compared with the state of the art. Index Terms— WBAN, communication security, ECG features, LPC, communication overhead 1. INTRODUCTION WBAN, a promising new research area, is defined as a net- work consisting of intelligent, low-power, micro technology sensors and actuators which can be placed on the body, pro- viding timely data [1]. The WBAN nodes are interconnected and connected to a coordinator node via a wireless communi- cation technology like Bluetooth and Zigbee [1]. Considered as a mistrusted channel, and while WBAN deals with sensi- tive medical data, securing the inter-sensor communications remains a major issue. Communication is encrypted with a shared symmetric key thats why a secure management and agreement of this shared symmetric key must be performed. Usual methods to secure inter-sensor communications have been based on symmetric key distribution or predeployment mechanisms. However the former requires secure key distri- bution scheme and the latter requires a set up and rekeying for every node management, whereas nodes in WBAN must be removed, added and tuned in a secure and transparent manner : without the user participation. The recent proposed solution, This work is supported by Telnet Innovation labs and the PASRI program funded by the European Union. to deal with key management problem, is physiological based security. The main idea of physiological based key agreement is to allow nodes belonging to the same WBAN to agree on a symmetric cryptographic key from the common physiological features. The collected features at different parts of the body are enough similar for an authentication purpose but not ex- actly identical to generate the same key sequence. This is due to noise caused by analog to digital converter and muscles contractions. The already used technique to overcome this problem is the fuzzy vault scheme [2]. The major weakness of this method is the size of the vault, a random set constructed to conceal the features, which is closely correlated to commu- nication overhead, primary cause of energy consumption. In this paper we investigate the use of linear prediction coding (LPC) to achieve feature set locking minimizing greatly the communication overhead. ELPA does not require any hiding of the features in a vault set which reduces greatly the mes- sage size. The proposed algorithm uses the already developed feature extraction stage AC/DCT [3]. ELPA is first assessed in the MIT-BIH Normal Sinus Rhythm Database [4] contain- ing recordings of healthy subjects and second in the MIT-BIH Arrhythmia Database [4]containing records affected by heart diseases to evaluate the robustness of the proposed method. The remainder of this paper is organized as follows. Sec- tion 2 presents an overview of the usual methods of secur- ing inter-sensor communication and the existing works in the new promising area: biological key. In section 3 we present the whole proposed scheme and detail each system bloc. Fi- nally we estimate the performance of the proposed system compared with the most known one the PSKA [5] in term of overhead and security. 2. RELATED WORK All the security requirements for communications can be ful- filled if a key is successfully and securely distributed. Usually used, predeployed keying mechanism was always the primary solution to secure communication in a Wireless sensor Net- work. It consists of distributing initial keys to all the partic- ipating sensors in the set-up phase [6]. The trend has then 23rd European Signal Processing Conference (EUSIPCO) 978-0-9928626-3-3/15/$31.00 ©2015 IEEE 81