# An On-Demand Fault-Tolerant Routing Strategy for Secure Key Distribution Network
## 1 Introduction
In addition, the faulty node may tamper with routing and intervene in other key distribution processes, reducing key distribution security [15]. The fault tolerance of routing protocols can be improved to ensure normal network functions and at the same time alleviate the urgent need to achieve fault tolerance of underlying software and hardware [16]. Since SSL-based SKDN has no dedicated channel restrictions, the node locations deployed by matched devices are highly decentralized and dynamic [9]. A well-designed design of the distributed routing strategy can reduce system operation and maintenance costs. Existing related research primarily focuses on reducing the possibility of faulty nodes passively eavesdropping on key [15]. For example, random routing is used to avoid a certain path where the faulty node is located or multi-path key distribution is used to ensure that at least one path in the multiple paths does not contain a faulty node to ensure that the key is not leaked [10]. The key generation rate of the current point-to-point SSL-based technique, however, is only in the range of megabits per second [5]. This method improves key confidentiality at the expense of consuming a large amount of local keys, which weakens availability. Additionally, there is no mechanism optimization for potential performance issues under broader fault scenarios like the above. Considering the aforementioned issues, this paper proposes a practical routing strategy for SKDN. By considering the path discovery and fault detection mechanisms in the routing strategy design, and the collaborative working methods between them, we ensure that the key distribution system has certain fault tolerance in the scenario of network layer fault. The main contributions of this paper are summarized as follows:* An on-demand path discovery mechanism in SKDN is proposed. Fault-free path discovery is performed when necessary, and appropriate paths are selected based on local key status to reduce control message propagation overhead and improve key resource utilization. * A fault handling method in the communication key distribution stage is proposed. After analyzing the location of the fault through the acknowledgment-based fault detection mechanism, based on the Dempster-Shafer (DS) evidence theory, the mass function of the weighted observation evidence is calculated to identify possible causes. A new round of path discovery can be used to isolate the cause of fault and transfer key status to improve the ability to handle exceptions. * The effectiveness of the proposed solution under different node scales and different proportions of faulty nodes is evaluated through simulation. Simulation results show that the proposed solution has improved in parameters such as packet delivery ratio and corrupted ratio, and the verification strategy has a certain practical value. The rest of this paper is organized as follows. Section 2 summarizes the related research articles. The system and problem model is introduced in Section 3. Section 4 describes the proposed solution. Section 5 presents the simulation result and discussion. The paper is concluded in Section 6.