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Security has become one of the key concerns for WSNs (Roy, Conti, Setia, & Jajodia, 2012; Du & Chen, 2008). This is because of the envisioned growth in utilizing sensor networks in a wide variety of environment, which are not benign. Most of the usage areas of WSNs are sensitive, and thus prone to different kinds of attacks (Karapistoli & Economides, 2012). A secured key management scheme is the pre-requisite for secured WSNs.
In the process of key management cryptographic keys are generated, stored, protected, transferred, loaded, used, and destroyed. The aim is to establish and maintain secure channels among communicating parties (Shanyue & Liqing, 2012). Typically, key management schemes use administrative keys for the secure and efficient (re-)distribution and, at times, generation of the secure channel communication keys to the communicating parties. Communication keys may be pair-wise keys used to secure a communication channel between two nodes that are in direct or indirect communications (Gagneja, 2012; Kang, Choi, & Park, 2012; Yin, Qiao-Yan, Zheng-Ping, & Meng, 2012) or they may be group keys shared by multiple nodes (Subash & Divya, 2011; Liu, Wang, Du, & Zhang; 2010; Yu, 2010). Network keys (both administrative and communication keys) may need to be changed (re-keyed) to maintain secrecy and resilience to attacks, failures, or network topology changes.
The design of a suitable key management scheme for a WSN is not trivial. Recently, the key management problem has been extensively studied in the context of WSNs. A good number of results have been attained (Shanyue & Liqing, 2012; Gagneja, 2012; Kang, Choi, & Park, 2012; Yin, Qiao-Yan, Zheng-Ping, & Meng, 2012; Subash & Divya, 2011; Liu, Wang, Du, & Zhang; 2010; Yu, 2010; Du, Guizani, Xiao, & Chen, 2009; Zhang, Liu, Lou, & Fang, 2006). Some of these schemes depend upon public-key algorithms (Du, Guizani, Xiao, & Chen, 2009; Zhang, Liu, Lou, & Fang, 2006). However, the low memory and energy physical constraints of sensor nodes limit the practice of this key management scheme in the real world. The key pre-distribution is another class of solution using symmetric encryption techniques to this problem. The design should be lightweight but compromise-tolerant.
Another major drawback in the existing scheme is generating a single key for communication between two sensor nodes. If the single key is captured by an adversary the communication between the node pair is permanently destroyed and thus the resilience of the network is less. To overcome this drawback partial keys are generated and used for communication between the node pairs. Each member node of a pair uses its partial keys in different order. Thus two separate links are established between the nodes. Because of partial keys and different order lists, if one of the nodes is captured by an adversary, there is no risk involved because using a partial key a message can be neither encrypted nor decrypted. Thereby the resilience of the network gets increased.
The aforementioned discussion dictates a need of a key management protocol for WSN that is simple yet robust. In this paper, we propose a key management protocol for cluster-based topology using partial keys pre-distribution to establish pair-wise keys. In WSN, sensor nodes are more power-constrained in terms of communication than computation. The amount of energy spent for a single communication can be used for hundreds of computations. This fact appeals to save a number of message transfers with the cost of few more computations. Thus, in the proposed key management protocol, the number of message transfer for establishing secret keys is remained the minimum.
Security and complexity analysis indicates that our scheme possesses the following properties: