## 4 Implementation and Discussion
### The Security Analysis  
The authentication messages are rendered immutable in the blockchain due to cryptographic hashing, whereby each block contains a unique hash derived from the previous block's data, creating an interlinked chain. This proposed system used the Ethereum blockchain that utilizes SHA-3 for its hashing operations. The inherent properties of cryptographic hash functions, such as collision resistance and irreversibility, contribute to the prevention of authentication message tampering or deletion. Furthermore, the Proof-of-Work (PoW) agreements method ensures agreement among the RSUs and the TAS on the validity of transactions before adding the authentication message to the blockchain. This decentralized agreement mechanism fortifies resistance against malicious alterations by requiring a majority consensus, making the authentication system robust and resilient against unauthorized modifications, thus ensuring the integrity and security of authentication for our proposed system. The integration of blockchain with Kerberos authentication in this proposed system introduces a noteworthy enhancement in privacy preservation by the implementation of smart contracts. It creates agreements or conditions between the RSUs and TASs. This condition must be fulfilled by the entities in order to perform the transaction. In our proposed system, the smart contract can automate the entities' registration, uploading the authentication message and requesting it. With the smart contract, we set that only the TAS entity can make an AuthenticationMessageUploading() request. On the other hand, RSU entities are able to make AuthenticationMessageAccessing() requests. This selective access ensures that only authenticated and authorized entities can access specific information, mitigating the risk of data exposure to unauthorized parties. Consequently, the use of smart contracts reinforces the privacy preservation entity by restricting access to sensitive information to only those entities that meet the predefined criteria, enhancing the security and reliability of the authentication framework within the context of vehicular communication. The verification process to add a new block involves all of the network users, including RSUs and TASs, to ensure a collective responsibility for transaction execution, engendering a heightened level of trust among participants. The decentralized nature of blockchain mandates a PoW consensus mechanism, requiring agreement from the majority before transactions are added to the distributed ledger. This distributed validation mechanism contributes to the transparency of the network, as all transaction records are permanently inscribed in the blockchain. This transparency fosters accountability and fortifies the integrity of the authentication system by enabling all users to verify transaction history. Consequently, the usage of blockchain in this proposed system augments trust through  
Figure 12: Memory size required for the block to store various authentication message. shared responsibility and fosters transparency by recording transactions on an immutable and accessible ledger, thereby bolstering the reliability of the authentication processes within vehicular communication. In the VANET system, malicious vehicles enter themselves into communication between two vehicles, impersonating them to gain access to information and inject false data. This type of attack is known as a man-in-the-middle attack, where the attacker eaves-drops on communication, alters messages, and breaches data integrity and privacy goals. The attacker may successfully pass through user authentication but will be blocked at the possession approval step. By inserting false information between genuine nodes or vehicles, the attacker undermines the trustworthiness of the data being exchanged, compromising network security. This attack poses a significant threat to the security standards of vehicle communication systems [48].