# Lightweight and Security-Enhanced Key Agreement Protocol Using PUF for IoD Environments
## 8 Performance Analysis
### Communication Cost Analysis  
This work compares and analyzes the communication costs of the proposed and relevant protocols incurred during key agreement and authentication. To evaluate the communication cost, this work assumes that the bit lengths of the ECC point, hash function, hyperelliptic curve, identity, random nonce, symmetric encryption/decryption, PUF challenge, and timestamp are 320, 256, 160, 160, 160, 128, 32, and 32 respectively. In [PERSON] et al. 's protocol [25], an operator transmitted \(\{B_{3},C_{2},S_{K_{1}}\}\); thus, the communication cost of the operator is 608 bits. The registration authority transmitted \(\{D_{1},D_{2}\}\) and \(\{C_{3},D_{4},S_{K_{2}},R_{5}\}\); hence, the communication cost of the registration authority is 1280 bits. The UAV transmitted \(\{R_{5},D_{3}\}\); thus, we computed the communication cost of the UAV as 416 bits. The total cost of the operator, registration authority, and drone is 2304 bits. In [PERSON] et al. 's protocol [26], the user transmitted \(\{U_{1},U_{2},U_{3},PK_{U},Tw_{1}\}\); thus, we computed the communication cost of the user as 960 bits. The ground-station server transmitted \(\{G_{1},G_{2},G_{3},Tw_{2}\}\); therefore, we computed the communication cost of the ground-station server as 800 bits. The drone transmitted \(\{D_{1},Auth,Tw_{3}\}\); hence, the communication cost of the drone is 544 bits. The total cost of the user, ground-station server, and drone is 2304 bits. In [PERSON] et al. 's protocol [27], the user transmitted \(\{PID_{i},PS_{j},F_{i}(t),C_{1},C_{2},C_{3},T_{1}\}\); thus, we computed the communication cost of the user as 1376 bits. The drone gateway transmitted \(\{PID_{i},C_{4},C_{5},C_{6},T_{2}\}\) and \(\{F_{i}^{new}(t),C_{11},C_{12},C_{13}\}\). Therefore, we computed the communication cost of the drone gateway as 2016 bits. The processor transmitted \(\{C_{7},C_{8},C_{9},C_{10},T_{3}\}\); hence, the communication cost of the processor is 1056 bits. The total cost of the user, drone gateway, and processor is 4448 bits. In [PERSON] et al. 's protocol [28], the user transmitted \(\{EU_{1},EU_{2},EU_{3},Pub_{Key},TS_{1}\}\); thus, the communication cost of the user is 960 bits. The GCS transmitted \(\{B_{1},B_{2},B_{3},TS_{2}\}\); hence, the communication cost of the GCS is 800 bits. The UAV transmitted \(\{U_{1},AUT_{N},TS_{3}\}\); therefore, we computed the communication cost of the UAV as 544 bits. The total cost of the user, GCS, and drone is 2304 bits. In [PERSON]'s protocol [13], the user transmitted \(\{A_{D},C_{M},G_{M},PK_{M},T_{1}\}\); hence, we calculated the communication cost of the user as 1120 bits. The GCS transmitted \(\{I_{M},PK_{M},A_{D},C_{M},H_{DM},T_{3}\}\) and \(\{Auth_{GCS},PK_{D}^{*},T_{7}\}\); thus, the communication cost of the GCS is 1984 bits. The drone transmitted \(\{Auth_{D},PK_{D}^{*},T_{5}\}\); therefore, the communication cost of the drone is 608 bits. The total cost of the user, GCS, and drone is 3712 bits. In the proposed protocol, the user transmitted \(\{HID_{M},V_{M},R_{1},T_{1}\}\); thus, we computed the communication cost of the user as 800 bits. The GCS transmitted \(\{C_{j},V_{G},R_{2},R_{3},T_{2}\}\) and \(\{R_{5},R_{6},Auth_{GCS},T_{3},T_{4}\}\); hence, the communication cost of the GCS is 1664 bits. The drone transmitted \(\{R_{4},Auth_{D},T_{3}\}\); therefore, the communication cost of the drone is 544 bits. The total cost of the user, GCS, and drone is 3008 bits. Table 7 and Figure 6 illustrate the comparative analysis of the communication cost for the proposed and relevant protocols. Although the communication cost of the proposed protocol is higher than that of [25; 26; 28], the proposed protocol offers more efficient computational costs and superior security features compared with these protocols. \begin{table}
\begin{tabular}{l l} \hline \hline
**Protocol** & **Communication Cost** \\ \hline
[25] & 2304 bits \\
[26] & 2304 bits \\
[27] & 4448 bits \\
[28] & 2304 bits \\
[13] & 3712 bits \\
**Proposed** & 3008 bits \\ \hline \hline \end{tabular}
\end{table}