# AI-Driven Optimization of Blockchain Scalability, Security, and Privacy Protection
## 2 Introduction to Related Technologies
### Blockchain
#### 2.1.2 Consensus Algorithm
```
1:System Parameters:
2:\(N=3f+1\), \(V=\{v_{1},v_{2},...,v_{N}\}\), \(primary=v_{k}\), where \(k=view\mod|V|\)
3:Initialize \(seq\_num=0\)
4:procedureClientRequest(\(c,m\))
5:\(\sigma=\text{Sign}(c,\langle\text{REQUEST},m,t\rangle)\)
6: Send \(\langle\text{REQUEST},m,t,c,\sigma\rangle\) to primary
7:endprocedure
8:procedurePrePrepare(\(m,t,c,\sigma\))
9:ifverify(\(\sigma\)) and \(seq\_num=n\)then
10: Broadcast\(\langle\text{PRE-PREPARE},v,n,d=H(m)\rangle\)
11:endif
12:endprocedure
13:procedurePrepare(\(v_{i}\))
14:ifreceived valid \(\langle\text{PRE-PREPARE},v,n,d\rangle\)then
15: Broadcast\(\langle\text{PREPARE},v_{i},n,d\rangle\)
16:endif
17:endprocedure
18:procedureCommit(\(v_{i}\))
19:ifreceived \(2f\)\(\langle\text{PREPARE},v_{j},n,d\rangle\)then
20: Broadcast\(\langle\text{COMMIT},v_{i},n,d\rangle\)
21:endif
22:endprocedure
23:procedureReply
24:ifreceived \(2f+1\)\(\langle\text{COMMIT},v_{j},n,d\rangle\)then
25: Send \(\langle\text{REPLY},v,t,r\rangle\) to client
26:endif
27:endprocedure
28:procedureViewChange(\(v_{i}\))
29:if timeout or primary fault detected then
30: Broadcast\(\langle\text{VIEW-CHANGE},v_{i},v+1,P,Q\rangle\)
31:endif
32:endprocedure
```  
**Algorithm 2** PBFT Consensus Process  
(5) Kafka  
The Kafka consensus mechanism is based on a reliable message queue and is commonly used in enterprise blockchain architectures, such as the ordering service in Hyperledger Fabric. Kafka offers high throughput, making it ideal for private blockchain applications with demanding performance requirements. Kafka-based systems rely on server-based message queues with minimal computational complexity, resulting in very low energy consumption, often far below 0.0001 TWh annually, particularly in controlled enterprise environments. However, it depends on centralized ordering nodes, introducing a single point of failure risk, which makes it unsuitable for decentralized blockchain networks [47]. (6) Raft  
Raft employs a leader election mechanism for log replication, making it suitable for small-scale distributed systems such as enterprise private blockchains. Its advantages include simple implementation and easy deployment while maintaining a high level of consistency. Raft-based consensus typically operates within private server clusters with modest computational loads, and its overall energy footprint is minimal, making it a low-energy consensus protocol. However, Raft's applicability is limited to small-scale environments, and its performance is influenced by the leader node. If the leader fails, consensus delays may occur. As Algorithm 3 shows, the Raft consensus algorithm is designed to achieve strong consistency across a distributed system in an intuitive and structured manner. It operates through several coordinated phases. First, leader election is initiated when a follower node does not receive a heartbeat signal within a timeout period, transitioning to a candidate and requesting votes from other nodes. A node becomes the leader if it secures a majority vote (at least \(\lceil N/2\rceil\)). Once elected, the leader is responsible for accepting client requests, appending them to its log, and replicating these entries to follower nodes via AppendEntries Remote Procedure Calls. Followers validate and append these entries, responding with acknowledgments. Upon receiving acknowledgments from the majority, the leader commits the entries and informs followers of the commitment. Raft ensures safety through leader exclusivity and log consistency and guarantees system termination under stable network conditions. (7) Paxos  
Paxos achieves consensus through multiple rounds of message passing, emphasizing data consistency. It is widely used in strong consistency databases such as Google Chubby and AWS DynamoDB. Paxos excels in high-fault-tolerance environments, ensuring stable consensus and maintaining data integrity. Despite its theoretical soundness, Paxos is considered energy-efficient in practice due to its use in tightly controlled data center environments.