## 3 Proposed Approach
Accordingly, the level whose distance is closer to the local coordinator requires the least communication cost for routing the health data. Let us consider that \(L_{0},\ L_{1},\ L_{2},\ \ldots\ L_{n}\) is the set of levels that belongs to the graph \(G(N,\epsilon)\). In each level, there is some set of nodes \(N_{i}\) that lies in the specific transmission range. Based on the constructed node table, each node transmits the route request (RREQ) to neighbors, and upon receiving the response, the virtual links are formed for the process of initial routing with the local coordinator. Afterward, the local coordinator initiates the process of key generation and nodes at level \(L_{0}\) with level \(L_{1}\) negotiate with each  
Figure 2: Procedural diagram of the proposed approach. other for securing data transmission. The local coordinator utilizes Station-to-Station (STS) protocol that uses a key agreement scheme [41]. It is based on the classic Diffie-Hellman algorithm to offer an authentication process for mutual key distribution and confirmation. The local coordinator generates a random number \(x\) and transmits the exponential \(g^{x}\) to the sensor node \(i\). Upon receiving, \(i\) generates a random number \(y\) and exploits exponential \(g^{y}\) to compute the exchanged key \(k=g^{xy}\). Moreover, \(i\) responds with the exponential \(g^{y}\) and an encrypted token that comprises its signature \(DS\), i.e., \(Ek(DS(g^{x},~{}g^{y})\). Afterward, the local coordinator computes a key \(k\), decrypts the token and confirms the \(DS\) using \(i\) public key \(R\). Similarly, the local coordinator transmits encrypted digital signature on the exponentials such as \(Ek(DS^{\prime}(g^{x},~{}g^{y})\). At the end, \(i\) confirms the encrypted signature of the local coordinator using \(k\) and the public key \(R\) of the local coordinator. The RNM-SC approach makes use of the Blum-Goldwasser cryptosystem, which is a semantically secure and asymmetric encryption system [42] for the generation of private-public keys. It chooses two large and independent prime numbers \(p\) and \(q\), and computes \(n\) as given in Equation (1). \[n=p\cdot q \tag{1}\]  
where \(n\) is Blum integer as public-key \(R\) and pair of \((p,q)\)\(\epsilon\) private key \(P\). Its security is based on the difficulty of factoring in the Blum integers. It is known as the most efficient probabilistic encryption algorithm comparable to the RSA encryption scheme for the measurement of speed and data increases [43]. In the next component, the RNM-SC approach utilizes the bidirectional search algorithm to determine the finest and next phased shortest path. Unlike most of the other solutions, it determines the optimal route in two stages simultaneously using the bidirectional method. One stage executes from the source node to the local coordinator, and the other stage from the local coordinator to the source node. The computation of the path from both directions depends on the heuristic function \(X(n)\). It is based on three factors, i.e., distance, transmission loss, and nodes' trust. To compute the distance, we use the Euclidean method from a source node to its neighbors \(D_{i,n}\). The transmission risk \(T_{r}\) is a product of transmitted packets over time \(t\) with a packet reception ratio (\(PRR\)). Let us consider if \(\sigma\) denotes the transmission rate and computed as given in Equation (2). \[\sigma=T_{plts}/t \tag{2}\]  
where \(T_{plts}\) denotes total transmitted packet from source to neighbor. Then, \(T_{r}\) is computed as given in Equation (3). \[T_{r}=\sigma\cdot(1/PRR) \tag{3}\]  
In Equation (3), if the value of PRR is increasing, then the transmission risk is lower. Accordingly, such a link is given high weightage for data transfer. In the end, node trust \(N_{tr}\) denotes its frequency, whose value is fetched from a local table to indicate how many times a particular node is selected for data forwarder. Accordingly, the higher frequency signifies the most reliable node for performing data routing.