## 4 Evaluation
### Security Performance
In the case of the verification process based on IOTA's Tangle structure, when 10% of all transactions that occurred were attacked, it took about 3.8 s to determine and deactivate them. These results confirmed that even if the race attack probability was increased from 10% to 50%, there was a similar average deactivation time of about 3.2 s. In comparison, the average deactivation time of the proposed framework at a race attack probability of 10% was about 1.3 s, which can be seen to be much faster than the existing system. Additionally, the proposed framework found that the average deactivation time of about 1.3 s was maintained even by increasing the probability of competing attacks from 10% to 50%. IOTA distributed ledger system uses a special DAG architecture called \"tags\" to group and distinguish transactions. A \"tag\" contains a reference to the two immediately preceding transactions and is used to categorize transactions together with a specific topic or purpose. \"Tags\" are a special feature of IOTA, but the process of forming these \"tags\" increases the time it takes to verify and propagate transactions. Additionally, this accumulation of transaction propagation and verification time delays ultimately increases the average deactivation time. This means that the verification process using the _miner_ and _prover_ of the proposed framework can verify malicious transactions much faster than existing systems. As a result, the proposed framework is more suitable for transaction processing in vehicular networks, where real-time updates are important. Second, Figure 9 measures the transaction throughput of the proposed framework according to changes in the race attack probability. Through previous experiments, it was confirmed that the existing distributed ledger system IOTA has a transaction deactivation time that is approximately twice as long as the proposed system. The reason why the transaction deactivation time is longer than the proposed system is because the IOTA system has slower transaction propagation, verification, and confirmation times. Therefore, in the second experiment, the performance of the proposed system was confirmed through the detailed verification of transaction throughput according to the attack scenario of the proposed system, rather than a comparative experiment with the existing system, IOTA. The results showed that the distribution of the final transaction confirmation time was between approximately 4.5 and 6 s. As can be seen in the experiment above, since it took about 1.3 s to verify a malicious transaction, it can be seen that more time was needed to confirm one transaction. Additionally, we can see that the confirmation rate distribution had almost no difference even as the attack transaction rate increased from 10% to 50%. This means that the proposed distributed ledger framework can support a certain level of transaction processing regardless of the proportion of malicious transactions among newly created transactions. Since the proposed framework guaranteed stable transaction processing against transaction attacks by malicious attack nodes, it can be confirmed that it is a secure system. Figure 8: The security performance evaluation result of the average deactivation time according to the probability of malicious transactions.