Title Page
Contents
Abstract 12
요약 14
Chapter 1. Introduction 15
1.1. Decentralized System 15
1.2. Overview and Contribution 19
Chapter 2. Preliminary Topics 23
2.1. Technological Overview of Blockchain 23
2.1.1. Blockchain Technology 23
2.1.2. Smart Contract 24
2.1.3. State Channel 25
2.1.4. Blockchain-based Security Deposit 31
2.2. Cryptographic Building Blocks 33
2.2.1. Decentralized Attribute-based Encryption 33
2.2.2. Attribute-Based Proxy Re-Encryption 37
Chapter 3. Multi-Authority Attribute-Based Encryption Secure against Collusion Attack 39
3.1. Introduction 39
3.2. Problem Statement 42
3.2.1. Related Work 42
3.2.2. Security Model and Goals 46
3.3. Proposed System 48
3.3.1. System Architecture 49
3.3.2. Phase 1. Deposit Setup 52
3.3.3. Phase 2. Get Ciphertext 54
3.3.4. Phase 3. State Transition 56
3.4. Security Analysis 59
3.4.1. Collusion Resistance 59
3.4.2. User Revocation 63
3.4.3. Decentralization 65
3.5. Performance Evaluation 66
3.6. Summary 70
Chapter 4. A Secure Data Sharing on the Decentralized Data Marketplace 71
4.1. Introduction 71
4.2. Problem Statement 74
4.2.1. Blockchain Scalability 74
4.2.2. Security Model and Goals 75
4.3. Proposed System 80
4.3.1. System Architecture 80
4.3.2. Phase 1. Setup 82
4.3.3. Phase 2. Channel Management 83
4.3.4. Phase 3. Close Channel 87
4.4. Security Analysis 89
4.4.1. State Privacy 89
4.4.2. Scalability 91
4.4.3. Revocation 92
4.4.4. Comparison 93
4.5. Summary 95
Chapter 5. Transparent and Accountable AI System 96
5.1. Introduction 96
5.2. Problem Statement 100
5.2.1. Related Work 100
5.2.2. Security Model and Goals 103
5.3. Proposed System 107
5.3.1. System Architecture 108
5.3.2. Phase 1. Initializing Project 110
5.3.3. Phase 2. Splitting Dataset 111
5.3.4. Phase 3. Distributing Dataset 114
5.4. Security Analysis 117
5.4.1. Unpredictable Dataset Splitting 117
5.4.2. Confidentiality of Test Dataset 119
5.4.3. Comparison 121
5.5. Performance Evaluation 123
5.5.1. Cost Efficiency 123
5.5.2. On-chain Overheads 125
5.6. Summary 128
Chapter 6. Conclusion 130
Bibliography 133
TABLE 3.1. Notations and descriptions. 52
TABLE 3.2. Computational cost notation 67
TABLE 3.3. Computational cost 68
TABLE 3.4. Costs required to execute the proposed contract SC and TSC 69
TABLE 4.1. Comparison from a performance perspective 94
TABLE 5.1. Comparison result 124
TABLE 5.2. Costs required to execute DDC implemented as an array 127
FIGURE 1.1. System Structures 17
FIGURE 1.2. Diagram depicts the overview of the thesis structure 22
FIGURE 2.1. State channel overview 27
FIGURE 2.2. Hashed Timelock Contract 32
FIGURE 2.3. Key generation phase in the Hur and Kang model 35
FIGURE 3.1. Overview of proposed dystem 50
FIGURE 3.2. Contract design for SC and TSC 51
FIGURE 3.3. Key generation phase in the proposed system 54
FIGURE 3.4. Data transaction overview 56
FIGURE 3.5. A state transition diagram of the proposed system 57
FIGURE 4.1. Proposed system architecture 77
FIGURE 4.2. Setup phase transaction structure 84
FIGURE 4.3. StateValidate Algorithm 86
FIGURE 4.4. Channel management transaction structure(grant access) 87
FIGURE 4.5. Channel management transaction structure (modify permissions) 88
FIGURE 4.6. State transition of off-chain channel 88
FIGURE 5.1. Proposed system overview 110
FIGURE 5.2. An overview of the dataset split 115
FIGURE 5.3. Comparison of on-chain overheads 128