## 6 Our New Model: A Robust Trustless and Privacy-Preserving Framework for VANETs
### The DLT Layer of the Architecture  
Figure 2 illustrates an EVM-based Decentralized Ledger Layer in a VANET that ensures secure, transparent, and decentralized data transfers. In this architecture, we employ a multiparty computation (MPC) network, where threshold signatures and threshold homomorphic encryption enable secure and private network data operations [13; 63; 75]. By integrating data collection from the physical layer to a DLT layer, this model establishes a network in which decentralized storage networks such as IPFS and Arweave, along with Layer 2 networks, connect each node to the others. Additionally, the mesh connects MPC nodes, which improves the resilience of the network and facilitates the dissemination of data. Smart contracts that have been pre-established are implemented on the Layer 2 network during the establishment phase, thereby enabling the transparency of network operations. The information obtained from the mesh undergoes processing, including analysis, cleaning, and packaging, prior to being transmitted to the DS (decentralized storage) system. For increased security, only the fingerprint of the published data (transaction identifier or content identifier) is transmitted to Layer 2; the original data remains within the DS system. By capitalizing on the benefits of decentralized storage and blockchain technology, this architecture guarantees the confidentiality and integrity of data, thus offering an all-encompassing resolution to the privacy and security obstacles encountered in VANETs. Multiple signers validate transactions through multiparty threshold signature schemes, and at least \(k\) out of \(n\) signatories must agree and sign the transactions to create valid transactions. This approach reduces potential fraud and minimizes the single point of failure by distributing transaction authorization power across multiple entities. Furthermore, the underlying threshold homomorphic encryption scheme uses key pairs to allow at least \(k\) people to decrypt a ciphertext in a \((\ell,m)\) threshold manner. Before presenting the DLT protocols, a setup protocol needs to be executed to create the necessary cryptographic keys for data sharing and analysis. **Procedure 2:** Key generation  
* **Step 1:*
* Execute threshold multisignature protocol between MPC nodes. * At the end of this protocol, each node will receive a private key share for later signing the transactions in a threshold manner. * The public key will be embedded into the smart contract. * **Step 2:*
* Execute threshold encryption protocol between MPC nodes. * At the end of this protocol, each node will receive a private key share for later decrypting and analyzing data in a threshold manner. * The public encryption key will be shared with the P2P layer, including RSUs and OBUs. Procedure 3 outlines the steps for creating and controlling a DLT protocol in a VANET (see Figure 2). In our framework, we utilize Ethereum as an example to securely distribute keys, verify transactions, and allow for direct computation on encrypted data. This ensures the reliability and accessibility of the blockchain ledger. **Procedure 3:** DLT Protocol  
* **Step 1:** Deploy smart contracts to an Ethereum-based Layer 2 ledger for the VANET architecture (e.g., Arbitrum, Optimism, zkSync, Scroll). * **Step 2:** Import public keys of MPC networks. * **Step 3:** Generate and distribute encrypted data to OBUs. Note that the data generated by OBUs are already anonymized and the correctness can be proven through ZKSNARKs. * **Step 4:** Sync and share encrypted data within OBUs, Roadside Units (RSUs), and Servers. * **Step 5:*
* Synced data are sent to the MPC network. * **Step 5.1:*
* The generated data will be analyzed. For example, some MPC applications allow to be analyzed before the decryption process. * **Step 5.2:*
* If required for further analysis, it may first be decrypted in a threshold manner. * **Step 5.3:*
* The final data will be cleaned and packed.