## 3 Proposed Key Exchange Protocol
### Practical Application of ECQV and One-Pass SKEM Methodologies  
Wireless sensor networks are subject to constraints, particularly regarding power and energy consumption, which can range from hundreds of milliwatts to the microwatt scale. We aimed to construct a protocol that supports low-power WSNs while providing sufficient security properties. To achieve this goal, the optimal approach is to reduce the computation on the node devices by applying symmetric block ciphers, such as AES, ASCON, and TEA, which offer a lightweight encryption and decryption process. Furthermore, the limitation in computation was also considered in the key generation process, and SKEM is a suitable scheme to generate and transport the key generation material at the least cost. By definition, the SKEM scheme requires asymmetric key pairs to generate symmetric session keys. Instead of applying the classic Diffie-Hellman method to generate and exchange generation materials for key pairs, the ECQV scheme significantly reduces the computing cost of authentication. As a result, a combination of ECQV and SKEM provided an optimal solution to reduce the computing effort at the node side while still applying strong asymmetric cryptography to establish secure communication. The idea of the proposed protocol was to utilize the advantages that SKEM offers:  
* The session key generation with signcryption gives assurance to the sender that the session key is available only to the recipient and assurance to the recipient that the key came from the sender. \begin{table}
\begin{tabular}{l l l} \hline \hline  & **Symbols** & **Corresponding Meaning** \\ \hline \multirow{5}{*}{Parameters} & \(ID\) & The identity \\  & \(G\) & The base point of ECC \\  & \(\mathcal{R}^{t}\) & A prime order of a specific elliptic curve \\  & \((\mathcal{C}^{t},\mathcal{R}^{t})\) & A challenge \(\mathcal{C}^{t}\) and its corresponding response \(\mathcal{R}^{t}\) at time \(t\) \\  & \(t,t_{n},t_{s}\) & Generated random values in \([1,q-1]\) \\  & \(R,R_{n},R_{s}\) & Curve points generated from random values \\  & \(\mathcal{C}ert_{N}\) & Implicit certificate designated for a node with \(ID_{N}\) \\ \hline \multirow{3}{*}{Keys} & \((k_{S},K_{S})\) & A private–public key pair of the server \\  & \((k_{N},K_{N})\) & A private–public key pair of a node with \(ID_{N}\) \\  & \(K\) & A symmetric session key \\ \hline \multirow{5}{*}{Functions} & \(\mathcal{H}_{1}()\) & Hash modulo function \\  & \(\mathcal{H}_{2}()\) & Hash function \\ \cline{1-1}  & \(F_{PUF}()\) & Function of a PUF \\ \cline{1-1}  & \(Enc()\) & Encryption algorithm using the symmetric key \(K\) \\ \cline{1-1}  & \(Dec()\) & Decryption algorithm using the symmetric key \(K\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Symbols and corresponding meanings. * One-pass key establishment provides a very efficient construction of session keys, which reduces the complexity of the handshake and computation at the sensor nodes. * The encrypted sensor data can be transmitted simultaneously with key generation materials, which favors the intermittent operation of the sensor nodes. According to [PERSON] (2018), it is important for one-pass key establishment protocols to have the security goal of key compromise impersonation. This is also true for OPKE based on SKEM, where only the sender contributes ephemeral data to the symmetric key generation. An adversary who can expose the key pair of the sender can permanently impersonate the sender. Therefore, the practical application of the SKEM-based OPKE relies completely on the secrecy of the asymmetric key pair. Moreover, in the deployment domain, the SKEM scheme publicly exposes the sender's identity \(ID\) in the exchange message. Without the existence of a trusted third party (a public key infrastructure) to generate key pairs for the sender and the receiver, any adversary can claim to possess that same \(ID\) and establish a shared key with the recipient.