# Utilising Acknowledge for the Trust in Wireless Sensor Networks
## 4 The Proposed Technique
### Description of the Proposed Technique  
As described in the dictionary, the meaning of trust is \"confidence in a person or thing's integrity, strength, ability, surety\" [36]. Therefore, trust must be automatically adjusted, reflecting the dependability changes in others. This concept is applied to create a framework for sensors in WSNs to make correct decisions for path selection. This paper presents a reactive trust-based routing method focusing on packet dropping attacks where misbehaving sensors try to reduce the network throughput. In this case, the malicious sensor transmits data link-layer acknowledgments (ACK\({}_{\text{DLL}}\)) to neighbor sensors, thus delaying the discovery of the attack. This kind of attack is one of the worst attacks where it delays attack detection. The proposed technique consists of four phases: Initialization, Path Search, Data Transmission, and Paths Maintenance phases. 1. Initialization PhaseAt the start of this phase, the sensors exchange the HELLO message with one another. A node receives a HELLO message for the first time, and it causes that node to update the information in its neighboring nodes table with this new information. As a result, at the end of the initialization process, every node will modify its adjacent node database. 2. Path Search Phase  
When a source needs to transmit data packets to a destination and does not have a suitable path, the source starts the path search process to find a valid path. In this phase, the source sends a modified RREQ packet containing a list of ignored nodes that the source sensor wants to isolate from the discovered path temporarily. In addition, the destination sensor may have this list and discard all paths that contain these ignored nodes. Upon REQUEST reception, a relay node (i.e., an intermediate node) compares its current, trustworthy value of the previous node with this value contained in the RREQ packet. The relay node updates it as soon as a current value falls below the RREQ packet's value. When the destination sensor receives the RREQ packet from multiple nodes, it chooses two-node disjoint paths with the greatest trust value, and unicasts RREPs contain the trustworthy path value back to the source, including the selected two routing paths. The source selects the highest trusted path as the main used for data transmission and the second as an alternate path. 3. Data Transmission Phase  
The source transmits its data packets over the main path, waiting to receive and in return from its downstream neighbor and from the destination over both primary and alternate paths, respectively. Each intermediary node stores its received information. If the source gets the \(\text{ACK}_{\text{DLL}}\) from its downstream neighbor as well as the through both the main and alternative routes, it positively updates the nodes' trust value and notifies the path nodes to update their trust value. If no is received through any of the routes, the source concludes that there is a misbehaving sensor in the routing paths and initiates the paths Maintenance Phase to identify and isolate any misbehaving sensors. 4. Paths Maintenance Phase  
The source node sends a high-priority Malicious Exploration Message (MEM) containing information about the lost data packet to the destination node through the main path in the Paths Maintenance phase. Each node that gets the MEM has its data packet information recorded in its IOP table, compared to the MEM information. After finding a match, it will send the MEM to the next node with overhearing to ensure that the neighbor node also forwards the MEM to the appropriate node. The node that found the mismatch will cease transmitting the MEM and will issue a high priority Malicious Discovery Message (MDM). The format of this message, such as MDM (discovering node ID, discovered node ID), with overhearing in the opposite direction, will be sent to the discovered misbehaving sensor toward the source or destination node.