## 2 Related Work
### Blockchain  
The blockchain is composed of cryptographic algorithms, consensus mechanisms, distributed data storage, and peer-to-peer communication. It possesses characteristics such as transparency, immutability, anonymity, and high security. Transactions are stored in blocks, and cryptography is used to ensure the security, reliability, and transparency of transactions [14]. These blocks are linked together in a chain. This is illustrated in Figure 3. The core feature of the blockchain is decentralization, which means there is no single central authority or administrator. Instead, it is operated by multiple nodes. Each node maintains a complete copy of the blockchain database and can verify and record transactions. When a transaction is initiated, the node broadcasts it to the entire network for validation. Validated transactions are included in a block, which is then broadcast to the entire network. When a block accumulates a certain number of transactions, it is added to the blockchain and permanently recorded, becoming unchangeable [15]. The blockchain has the following characteristics [16; 17]:  
* Decentralization: The blockchain system operates without a central authority, and all nodes have equal power. Nodes can communicate and transact with each other. This decentralized feature makes the system more democratic and open, reducing the risk of a single point of failure.
* Immutability: Transactions recorded in the blockchain are packaged into blocks and linked together. Each block contains validation information from the previous block, forming an expanding chain. Any modification to the content of a block would affect the entire blockchain and require changing the content of all subsequent blocks. This immutability ensures that data in the blockchain have a high level of trustworthiness and security.
* Openness: On a fully public blockchain, anyone can access and query the records on the chain. Although the data are anonymous, transaction records and balances of users are publicly transparent.
* Non-repudiation: The data structure of the blockchain is permanent and immutable. Once data are recorded on the blockchain, they cannot be deleted or modified; only new additions are possible. When a transaction is confirmed, its record is broadcast to all nodes in the blockchain network, ensuring that all nodes have the same information.  
\begin{table}
\begin{tabular}{l l} \hline \hline
**id** & CredentialID. \\  & authenticatorData: Data related to the authenticator device during the verification process. \\  & clientData: Data provided by the client to the authenticator device for generating the credential. \\  & signature: The signature generated by the private key associated with the credential. \\
**type** & The type of the credential, which is public key. \\ \hline \hline \end{tabular}
\end{table}
Table 5: The parameter list for PublicKeyCredential in FIDO2 login.  
Blockchain technology solves the problems of traditional identity verification, and the thesis [18] proposes a smart contract-based identity management and authentication model with several advantages. It provides higher security as identity information is stored on a decentralized blockchain network, making it difficult to be attacked or tampered with. It also eliminates the need for intermediaries, allowing users to directly perform identity verification, thereby improving efficiency and convenience. This demonstrates the potential and future applications of the blockchain in the field of identity verification. With the continuous development and maturity of blockchain technology, we can anticipate seeing more innovative applications in various identity verification scenarios in the future.