# Symmetric-Key-Based Security for Multicast Communication in Wireless Sensor Networks +
###### Abstract  
This paper presents a new key management protocol for group-based communications in non-hierarchical wireless sensor networks (WSNs), applied on a recently proposed IP-based multicast protocol. Confidentiality, integrity, and authentication are established, using solely symmetric-key-based operations. The protocol features a cloud-based network multicast manager (NMM), which can create, control, and authenticate groups in the WSN, but is not able to derive the actual constructed group key. Three main phases are distinguished in the protocol. First, in the registration phase, the motes register to the group by sending a request to the NMM. Second, the members of the group calculate the shared group key in the key construction phase. For this phase, two different methods are tested. In the unicast approach, the key material is sent to each member individually using unicast messages, and in the multicast approach, a combination of Lagrange interpolation and a multicast packet are used. Finally, in the multicast communication phase, these keys are used to send confidential and authenticated messages. To investigate the impact of the proposed mechanisms on the WSN, the protocol was implemented in ContikiOS and simulated using COOJA, considering different group sizes and multi-hop communication. These simulations show that the multicast approach compared to the unicast approach results in significant smaller delays, is a bit more energy efficient, and requires more or less the same amount of memory for the code.  
have been made [1; 2; 3]. However, these standardizations often do not include mechanisms for key management, in particular not for group-based communication. Nevertheless, key management is essential in this whole procedure to send secure and authenticated messages.  
Often it is considered that the key is pre-established before deployment. For instance, we also considered such assumption in [4], where we studied the impact of including secure and authenticated communication for a 6 LoWPAN-based WSN, connected via an edge router to the central server. For this purpose, we implemented the AES-GCM mode in the different entities. We concluded that the impact of the security mechanisms into the global system is acceptable and its relative impact even decreases when the number of hops increases and/or the number of messages decreases. Also, the memory footprint of the global system is quite small and limited to 6% of the total.  
Minimal security features to be established are confidentiality, integrity, and authentication. Efficient mechanisms are required, due to the limited bandwidth, processing power, storage capacities, and available power. Efficiency implies scalability and adjustability [5]. Scalability in the sense that the key management protocol is able to include additional nodes in a secure manner during the network's lifetime. Adjustability implies a proper mechanism to deal with network condition changes.  
We will use the architecture established in [6]. In this framework, group-based communication is organized through the integration of a network multicast manager (NMM), which allows for a reduced bandwidth usage with a minimal memory footprint, by integrating multicast groups in the publish/subscribe paradigm.  
The remainder of the paper is organized as follows. Section 2 provides an overview about the related work. Section 3 explains the network architecture with some key definitions and assumptions used. In Section 4, we summarize the different phases of our scheme in normal mode. Sections 5 and 6 respectively describe the implementation details and the corresponding efficiency. Finally, Section 7 concludes the paper.