## 2 WSN Routing and Attack Mechanism  
The LPP for WSNs first appeared in [1]. With the development of IIoTs and extensive applicability of WSNs, the topic of LPP has received widespread attention in the recent decade. Well-known routing ideas available in the LPP literature are categorized as:  
**Random Walk Routing:** In this routing, packets are sent from source node to sink node over random walks or paths [4; 5]. This is one of the simplest forms of routing, where the sensor nodes do not calculate or store much information. However, this routing often leads to high overall energy consumption due to longer source-to-sink path length [6]. Typically, random walk routing is deployed with additional protocols. For example, see [7; 8; 9], which involves random walk routing with other routing methods. **Phantom Routing:** In this routing, packets are sent from source node to sink node in two phases [1; 10]. In the first phase, the packets are sent from source node to phantom node (a node in the network that is typically neither a source nor a sink). In the second phase, the packets are sent from the phantom node to sink node. Typically, in the first phase, random walk routing is used, and in the second phase, shortest path routing is used. The usage of multiple phantom nodes is proposed in [11]. The key difficulty of phantom routing is the selection of phantom nodes. A technique based on sector domain to increase positional diversity of phantom nodes is proposed in [12]. **Fake Packets Routing:** In this routing, along with the real packets, the network is induced with fake packets. The idea is to camouflage real packets among the fake packets. The key difficulty in this routing is the right number of fake packets to be induced into the network. Furthermore, fake packets consume network resources, including energy and time. Applications of fake packets can be seen in [13; 14]. **Ring Routing:** The idea in this routing (see [15]) is to induce disjoint rings (cycles) while transmitting the packets from source nodes to sink node(s). Every disjoint ring contains a master node (bus node) that is responsible for forwarding the packets from source node to sink node (actual route). Simultaneously, the bus nodes on the actual route send additional packets to a ring of nodes. This additional set of packets sent on the disjoint rings confuses the adversaries. The further applications of ring routing can be seen in [16], and energy efficient ring routing can be seen in [17]. **Multi-Path Routing:** In multi-path routing, data between source and sink nodes are sent via multiple disjoint paths. In order to avoid tracing back of the paths by the adversary, some deviation mechanisms are proposed. For example, a random stride routing is proposed in [18], and a constrained random routing is proposed in [19]. The constrained routing limits the energy usage in the network. Typically, multi-path routing without careful deployment suffers from high energy consumption during the transmission. Thus, several flavors of this category focusing on reduced energy consumption in multi-path routing are proposed in [20; 21; 22]. **Network Encoded Routing:** In this routing, packets are re-encoded, split into multiple small packets, or integrated into one big packet during the transmission. **Directional Routing:** Directional routing consists of directional antennas and/or transceivers. The underlying assumption is that the directional routing makes eavesdropping expensive. In [23], the usage of directional antennas along with transmitting power control and information compression is depicted. More usage of directional transceivers is presented in [24]. **Data Rule Routing:** Data rules are nothing but mobile agents. The routing mechanism is as follows: a source node sends packet to a randomly selected intermediate node. The intermediate node forwards the packet to a data mule. The data mule randomly moves around the network and forwards the packet to another intermediate node. Finally, the intermediate node forwards the packet to the sink node.