# A Communication-Efficient Secure Routing Protocol for IoT Networks +
###### Abstract  
This paper proposes a secure routing protocol based on an ad hoc on-demand distance vector to simultaneously achieve communication efficiency and security. Many studies have discussed secure protocols. However, conventional protocols tend to exhibit low communication efficiencies owing to the long packets required by digital signatures, specifically in large-scale networks. Hence, our proposed method aims to allow the intermediate node to initiate a route reply (RREP), which is prohibited in conventional protocols because of digital signature restrictions. Based on an ID-based signature, the proposed protocol allows each intermediate node to hold a packet received from a specific node in the past. Each node then appends it to the route request of another node and generates its own signed RREP. This procedure guarantees that a third party holds the route to the destination. Theoretical evaluations demonstrate that the proposed method outperforms the communication efficiency of conventional secure protocols. We measured the time required for routing (i.e., the sum of communication and cryptographic calculation times) using a Raspberry Pi with C language. We show that the proposed protocol can improve the average routing time by more than 3\(\times\) compared with conventional methods when 30 relay nodes are randomly distributed in a 300-square meter area. A 2022  
been recently discussed. The AoI is an information-theoretic criterion expressing the freshness of the information of interest [7]. Communication design based on AoI enables IoT networks to collect massive amounts of sensing information with low latency. As previously discussed, recent trends in IoT show the requirements for low-latency communications in large-scale networks. In MANETs, nodes must construct a route from the source to the destination nodes in advance. However, typical routing protocols (e.g., ad hoc on-demand distance vector (AODV) and dynamic source routing (DSR)) allow any node to freely join the network. Thus, these protocols are vulnerable to cyber-attacks from malicious nodes such as communication interceptions, route falsifications, and black hole attacks [8]. Several of the above-mentioned applications of MANETs manage privacy and safety information; therefore, in addition to the communication issue, the security of MANETs is a key topic in the future IoT systems. Various studies have proposed secure routing protocols to improve security issues in MANETs [9; 10; 11; 12; 13; 14; 15; 16; 17; 18]. The different types of secure routing protocols can be roughly divided into (a) cryptography-based approaches and (b) trust-based approaches. In general, cryptography-based routing protocols require nodes to append a digital signature to the routing packet in order to guarantee the validity of the packet and prevent forgery and falsification [9; 10; 11]. A digital signature can deal with attacks. However, it degrades communication efficiency because cryptographic information is added to the relayed packet hop-by-hop. This feature leads to an increase in communication overhead and a low packet delivery rate (PDR). Furthermore, due to the limitations of packet authentication, related methods must perform end-to-end communication whenever necessary to ensure the integrity of routing packets. This feature tends to increase the number of hops as the network size increases, as intermediate nodes are prohibited from initiating the route reply. Most wireless devices in MANETs have limited computational capabilities and communicate using finite wireless resources. Therefore, a secure routing protocol should work with a limited increase in the routing packet size. In contrast, trust-based protocols [16; 17; 18] can prevent malicious nodes from joining networks while preserving both computational and communication efficiencies by introducing a trust value based on the past behavior of the target node.