## 6 Security and Efficiency Analysis
### Efficiency Analysis  
In order to confirm the accuracy of the proposed protocol and to perform efficiency analysis, the WiSeN sensor node [64] that we developed earlier was used. A WiSeN node (Figure 6) has a battery connection and multiple plugs. In addition, a WiSeN node is pluggable to SIM900 GSM/GPRS nodes for sending data to distinct places. In the WiSeN sensor node, MSP430G2553 and IEEE 802.15.4 [65,66] CC2530 ZigBee modules are used. Also, WiSeN has a SHT11 temperature-humidity sensor on board. \begin{table}
\begin{tabular}{p{56.9 pt} p{113.8 pt} p{113.8 pt}} \hline
**Threat** & **Description** & **Analysis** \\ \hline \multirow{4}{*}{Non-Repudiation} & After the data transfer from the source to the target, the source cannot deny that the data are sent and the target cannot deny that it has received the data. & In the proposed protocol, there can be no denial as communication is only through known private keys and digital signatures. \\ \hline \multirow{4}{*}{Mutual Authentication} & In an authentication protocol, two parties confirm each other’s identity at the same time. & The proposed protocol provides mutual authentication between SN-CN and CN-BS. Since PBK, PVK, ID, IDcard, smart contract with ECDSA are always used in the communications made by all nodes connected to the blockchain network, both the sender and the receiver are verified bilaterally. In addition, all transactions made are registered in the BCN and can be securely traced. \\ \hline \multirow{4}{*}{Sybil Attack} & It is a security threat that occurs when an attacker tries to take over the network by creating multiple pseudonymous identities. & In the proposed protocol, all nodes (SN, CN) in the network are registered in the BCN. All nodes have their own unique ID, PBK, PVK, IDcard information defined and this information is also registered in the BCN. During communication, nodes are verified with smart contract using this information. At the same time, this process is safer because the private blockchain structure is used, which is permission-based. It is not possible for a node with a false identity to enter the network or impersonate nodes. \\ \hline \multirow{4}{*}{Spoofing Attack} & A situation where an attacker is successfully identified as another identity by falsifying data. & As explained in the data integrity, mutual authentication, and sybil attack parts, the attacker cannot perform the relevant attack because it needs to know the private information of the nodes in the network. \\ \hline \multirow{4}{*}{Message Substitution Attack} & It refers to an attacker replacing a message. & In the proposed protocol, key and signature are used in all sent messages. If the Attack modifies a message, they must sign it with a valid private key. However, since these keys are only in their owners and they are registered in the BCN, message substitution attacks cannot succeed. \\ \hline \multirow{4}{*}{Message Replay Attack} & The repetition of a valid data transmission by the attacker. & In the proposed protocol, an attacker must be authenticated before he can send a message. Only authenticated nodes can send messages on the network. On the BCN side, all blocks have a timestamp and a consensus is required for blocks to be valid. Therefore, the attacker’s message is not accepted by the consensus mechanism. In this way, data freshness is ensured. \\ \hline \multirow{4}{*}{Man in the Middle Attack} & It is a type of attack in which the attacker secretly transmits or changes the communication between two parties communicating directly with each other. & Since the attacker does not know the ID, PBK, PVK, IDcard information of the nodes, it will not be able to get permission from the authentication protocol to access the network or the attack process will not be terminated. \\ \cline{1-1}  & It is a type of attack that aims to temporarily or indefinitely disrupt the services of the network so that a node or network resources cannot be reached by the actual users. \\ \hline \end{tabular}
\end{table}