A Hybrid Secure Scheme for Wireless Sensor Networks against Timing Attacks Using Continuous-Time Markov Chain and Queueing Model  
[PERSON]  
1 Department of Mathematics and Computer Science, Freie Universitat Berlin, Berlin 14195, Germany;  
[EMAIL_ADDRESS]
2 Shenzhen Institute of Radio Testing & Tech., Shenzhen 518000, China;  
3 Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen 518055, China;  
[EMAIL_ADDRESS]  
[PERSON]  
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eavesdropping, denial of service, etc. Unfortunately, traditional security mechanisms with high overhead are not feasible for the resource-constrained sensor nodes [6]. An important issue of WSNs is how to preserve sensitive measurements taken from everyday life where data privacy is an essential aspect. In many scenarios, the confidentiality of propagated data can be considered critical. For instance, in a healthcare system, data from sensors might measure patients' health information, such as heartbeat and blood pressure details. Data privacy can be simply defined as a process in which private data can be overheard and decrypted by adversaries or other trusted participating sensor nodes [7], but it can still provide a mechanism that prevents them from recovering sensitive information, i.e., control disclosure of any information about the data.  
Securing cryptographic implementations in WSNs against side-channel attacks is one of the most important challenges [8], which is not covered by traditional notions of cryptographic security [9]. Among side-channel attacks, timing attacks, whose remote feasibility has been proven by [PERSON] and [PERSON] [10; 11], make a practical threat against sensor network systems. Energy is an essential resource of WSNs, so the implementations of cryptographic algorithms in such systems often perform computations in non-constant time due to performance optimization. The timing attack involves algorithms that have non-constant execution time, and this can potentially leak secret information. As represented in [12], the operating system running on the sensor nodes is event-driven and extremely optimized in terms of memory consumption, which suggests that the timing side-channel is practical in WSNs.  
In this paper, we propose a secure scheme to defend WSNs from timing attacks. The rekeying process with an optimal rate is introduced into the WSNs, and random paddings are interposed in the processing time to mitigate the information leakage of the timing side-channel. Our contributions are now summarized as follows:  
* In order to proceed to a quantitative treatment of the performance-security tradeoff of WSNs, we propose a hybrid continuous-time Markov chain (CTMC) and queueing model for the system under the specific threat of timing attacks.
* We have shown the measures' formulation, including both security and performance attributes, and the optimal tradeoff between the two.
* Experimental evaluations demonstrate the effectiveness of the random padding countermeasure against timing attacks and the tradeoff improvement one can obtain from the proposed scheme.  
The remainder of this paper is structured as follows. In Section 2, we overview the current state-of-art related works. Section 3 shows the considered multi-gateway clustered topology and rekeying management method as the system architecture. A hybrid model that employs the hybrid CTMC and queueing model for a WSN under timing attacks is proposed in Section 4. In this section, we describe the state-transition model and the scheduling method. The system metrics on which the evaluation is based are addressed in Section 5. Section 6 gives the theoretical model analysis of the security and performance attributes using quantitative assessment methods. Experimental evaluation of the general WSN system is presented in Section 7. Finally, the paper is concluded in Section 8.