**Abstract**

Key management is one of the most important tasks in wireless mesh network. This service is responsible for key generation, distribution, and key exchange in a cryptography-based system. Due to the shared nature of WMNs and absence of globally trusted central authority, key management becomes more challenging. This chapter introduces several key management methods that can address these challenges. The fundamental approach is the secret sharing scheme created by A. Shamir, which effectively distributes keys to all participants' network. Based on Shamir's scheme, many authors proposed other algorithms to secure the communication channel in such a way that adversary cannot steal any information about the secret. In addition, in this chapter, a new secret sharing method using real-time synchronization among transceiver devices is presented. In this method, each node generates its key depending on its physical information and the real-time clock. Therefore, public and private keys can be managed efficiently for data encryption and prevent several external attacks to WMNs. A specific protocol is proposed to secure keys while transferring between devices to prevent internal attacks.

**Keywords:** wireless mesh network, key management, wireless encryption, secret sharing, cryptography

### **1. Introduction**

WMNs are increasingly becoming a prominent architecture that are used in various applications such as home networking, transportation, enterprise networking, etc. [1]. WMNs are very vulnerable to be attacked by opponents. There are three types of attack: active attacks, passive attacks, and message distortion [2]. In order to guarantee the security of data in such networks, cryptography is one of the most popular choices. Therefore, key management services are in demand.

Key management refers to process of cryptographic key generation, distribution, and storage [3]. In addition, the responsibility of key management is establishment of trusted and secure communication between nodes. Due to the unique nature of WMNs, there are three challenges that many existing key management schemes are facing [4]. Firstly, it is difficult to share, transport, and update keys because of the lack of infrastructure in WMNs. Secondly, a distributed certificate authority (CA) model is needed to tackle the absence of fixed central infrastructure in WMNs which is not suitable for public key infrastructure (PKI). Finally, the concern of scalability is undeniable to take advantage of being expandable of WMNs (nodes can join or leave the network).

Many researchers have proposed numerous approaches for group key management. One of the most common group key management methods is secret sharing introduced by Shamir [5]. The schemes allow a master key (secret) to be shared to all authenticated users, but it can just be reconstructed when a node has enough number of shares. Combining with Shamir's method, Li and Xin used the self-certified public key system for proposal of a distributed key management approach [6]. All keys are generated and managed in a self-organizing way within the network, while there is no need of prebuilt trusted relationship between nodes. Lan Yun et al. introduced secret sharing-based management (SSKM) based on Shamir's scheme [7]. The proposed method dynamically generates a different key based on different polynomials from the base station in different periods which can protect the network from the compromised nodes and reduce the high probability of the common key. Filippo Gandino et al. [8] proposed a new key negotiation routine to deal with the case when a node is compromised by adversary. The goal of this algorithm is to reduce the time for the initialization phase as well as reduce the probability of compromised master secret. Singh et al. [9] combined Shamir's scheme and encryption method together by using only hash and XOR function to reduce the overhead for realistic WMNs which have limited resource. All attempts of researchers are to enhance security reliability for key management.

The remaining sections of this chapter are organized as follows. The detail approaches of other authors are introduced in section II, III, and IV. In section V, we proposed a new key management method using real-time synchronization among transceiver devices. In addition, we present our experiments and the result analysis. Finally, the conclusion is drawn in Section VI.
