# AI-Driven Optimization of Blockchain Scalability, Security, and Privacy Protection
## 2 Introduction to Related Technologies
### Blockchain
#### 2.1.2 Consensus Algorithm  
The reliability of the blockchain system is highly dependent on the design of the consensus mechanism [39], a technology that realizes efficient transaction verification by coordinating the protocols among network nodes and is decisive for maintaining data consistency and operational integrity. Currently, blockchain can be categorized into public, private, and consortium chains based on permission scope and access control mechanisms [40]. Each type exhibits distinct characteristics and serves different application scenarios. Public chains, known for their high level of decentralization, transparency, and censorship resistance, allow any participant to join, validate transactions, and contribute to the consensus process. They are widely utilized in areas such as cryptocurrency transactions, decentralized finance, and non-fungible tokens [41]. However, the open nature of public chains often leads to scalability and energy consumption challenges. In contrast, private chains operate under restricted access where only authorized participants can read, write, or audit the blockchain. They prioritize data security, privacy protection, and efficient management, operating with a significantly lower degree of decentralization. This model is particularly suitable for industries such as finance, healthcare, and supply chain management, where regulatory compliance, sensitive data handling, and operational efficiency are critical. Consortium chains, also known as federated blockchains, integrate features from both public and private chains. They are governed by a group of pre-selected nodes or organizations, achieving a balance between multiparty cooperation, transparency, and controlled decentralization [42]. Consortium chains offer enhanced performance, scalability, and trust through partial decentralization while maintaining higher privacy standards compared to public chains. Their strengths in traceability, auditability, and governance mechanisms facilitate transaction tracking, cross-organizational collaboration, and comprehensive historical record management, making them ideal for applications in interbank clearing, supply chain traceability, and cross-border payments. Table 4 presents a detailed comparison of blockchain categories in terms of decentralization level, security, scalability, transparency, and typical application scenarios [43]. Consensus algorithms play a crucial role in distributed systems [44], particularly in blockchain technology, where they ensure that all nodes in the network agree on the validity of transactions [45]. Different consensus mechanisms exhibit various strengths and weaknesses, influencing aspects such as security, energy consumption, throughput, and decentralization. The following Table 5 provide a detailed discussion of several mainstream consensus algorithms. \begin{table}
\begin{tabular}{l c c c} \hline \hline
**Type** & **Public Blockchain** & **Consortium Blockchain** & **Private Blockchain** \\ \hline
**Participants** & Anyone & Consortium members & Internal to an organization \\
**Consensus Mechanism** & PoW / PoS / DPoS & PBFT / Kafka / BFT & Raft / Paxos \\
**Incentive Mechanism** & Required & Optional & Not required \\
**Degree of Decentralization** & Decentralized & Partially decentralized & (Partially) centralized \\
**Data Consistency** & (weak) consistency & (strong) consistency & (strong) consistency \\
**Network Scale** & Large & Relatively large & Small \\
**Typical Applications** & Cryptocurrencies & Payments & Auditing \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Comparison of blockchain categories. PoW achieves consensus through competitive computation of cryptographic hash puzzles, ensuring transaction security and immutability. It is widely used in public blockchains such as Bitcoin. The primary advantage of PoW is its high security, effectively preventing Sybil attacks and maintaining network decentralization. However, PoW requires significant computational resources, leading to high energy consumption.