# Blockchain-Based Authentication in Internet of Vehicles: A Survey
## 4 Blockchain-Based Authentication Schemes in Vehicular Networks
### Consortium Blockchain-Based Authentication Protocols
A consortium blockchain is deployed during the dynamic group key updating process to record the identity of the participating vehicles in order to provide traceability of vehicle's historical data when needed. Formal security analysis proves the resiliency of the proposed scheme to chosen message attacks and replay attacks. Low storage, communication, and computation overheads are also recorded through deep performance evaluation. The authors in [139] designed a novel data structure based on the idea of the Unspent Transaction Output (UTXO) adopted in Bitcoin in combination with a group of online operations, namely, issue, transfer, query, and revocation. The system framework consists of two layers: the entity layer which is mainly the vehicles and RSUs that need authentication service and the trust layer represented by the TAs and the consortium blockchain. Each TA is responsible for managing a dedicated group of entities which all together form an organization. When creating a new block, a sufficient number of organizations must sign it to be accepted to the consortium blockchain. However, the authors developed the use of tokens in the UTXO to serve as a one-time guarantee for the authenticity of an entity instead of using incentives as in Bitcoin. Once an entity receives a token from another entity in the public ledger, this not only means an authentication request being issued, but also proves or guarantees the authenticity of the dedicated sender. The UTXO data structure is formed by three key items, namely, basic, in, and out items. The basic item includes the transaction id, the operation name, the timestamp, and the signature of the requester to prove its ownership. The in item represents the information of the sending entity while the out item includes information related to the receiving entity. The authors define several operations that are as follows. The Issue operation is used by trusted authorities to generate new tokens for the entities, which can take place only upon two circumstances: the initial enrollment of a vehicle and periodically generated for well-behaved entities. Similarly, the Query operation can be used to retrieve the UTXO of a transaction on the blockchain through transaction id in order to check the trustworthiness of a sending entity. The Revoke operation is the key operation introduced by the authors for revocation management instead of the conventional certificate revocation list that implies extra storage and computation overheads. However, the main operation used for authentication purposes is the Transfer operation and the procedure is as follows: when an entity \(E_{i}\) sends an authentication request to Entity \(E_{j}\), Entity \(E_{j}\) extracts the unique transaction id from the request message and uses it to query and retrieve the transaction UTXO from the blockchain. Then, the identities of the sending and receiving entities in the retrieved UTXO are compared against the ones received in the authentication request to check their legitimacy. If confirmed, the existence of the UTXO should be verified in the receiving entity's (\(E_{j}\)'s) local database to check for token reuse. If the UTXO does not exist, the authentication is successful and it is recorded immediately in the database for future authentication references, otherwise, the authentication is rejected. In addition to resisting replay attacks (due to the use of timestamps and one-time tokens), the scheme prevents man-in-the-middle attack, identity revealing attack, as well as authority abuse attack. The above-mentioned consortium blockchain-based authentication schemes can be found in Table 6 for the ready reference. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Ref.