近年來，區塊鏈技術因其能在分散式的網路環境下取得全域共識而備受矚目，並進一步應用於支付系統中。而區塊鏈技術根據其特性可分成兩類，可用性優先與一致性優先演算法。前者的代表是證明取向的協定如比特幣，具備隨時可用的特性但其確認時間過長且容易遭受雙花攻擊；後者則為拜占庭容錯取向的協議如瑞波幣，其確認時間較短且保證共識結果的正確性，但不適用於大範圍的開放網路環境。作為支付系統的關鍵技術，上述兩種區塊鏈技術都明顯還有改善的空間。
為此，一個拜占庭容錯取向協議的改良版：聯邦拜占庭協議，便進一步被提出，而恆星共識協定因採用聯邦拜占庭協議將可在大範圍開放式網路環境下保證共識的一致性。儘管如此，恆星共識協定仍面臨著單點失效導致系統停滯進而造成可用性喪失的問題，而系統壟斷的問題也將嚴重影響其在支付系統上的實用性。為此，本論文基於聯邦拜占庭協議提出了可持續聯邦拜占庭協定來解決上述問題。首先，本協定優化了聯邦拜占庭協議中信任切片的選擇演算法，藉此顯著降低發生單點失效的可能性。再者，本協定採用了多數見證人概念來保證全域共識的一致性；而週期性更換信任切片與隨機見證人方法的採用更可進一步防止恆星共識協定所遭遇的系統壟斷；最後，本協定的信任切片重組演算法讓系統停滯發生時能自動進行修復，為系統提供了更好的可用性。
經過系統分析與模擬實驗證實，本論文提出的協定不僅能透過多數見證人概念保證共識的一致性，在信任切片的選擇上也明顯較恆星共識協定有著更高的可容錯性，不易發生系統停滯；另外，與恆星共識協定相比，本協定中參與共識機制的成員更加多元，讓系統不容易被少數節點所把持；最後，在模擬大量節點發生故障的情況下，恆星共識協定易因故障節點過多而造成系統服務中斷，而本協定則會在系統停滯時自動偵測並協助系統恢復運行，因此具有較優秀的可用性。因此，本論文提出之可持續聯邦拜占庭協定將是最適用於開放網路環境交易系統的區塊鏈技術。

Recently, blockchain emerges as a promising technology because it can reach a global consensus in distributed networks. Therefore, more payment applications try to introduce blockchain into their systems. Generally, blockchain technology can be divided into two types, liveness-guaranteed-first and safety-guaranteed-first algorithm. The former, such as proof-based protocols like Bitcoin, can easily reach a probabilistic consensus but has long confirmation time and tends to suffer from double-spending attacks. The latter, such as BFT-based protocols (Byzantine Fault Tolerance) like Ripple, has short confirmation time and ensures the consistency of consensus but is unpractical in large-scale networks. As a result, none of these blockchain technologies is capable for payment applications.
Hence, a variation of BFT-based protocols, Federated Byzantine Agreement (FBA), is proposed, and a FBA-based consensus protocol, Stellar, is developed to reach a consistent consensus in large-scale networks. However, Stellar might be stuck by single point of failure leading to the loss of system liveness. Moreover, the system dominance problem also makes Stellar unpractical to be exploited in a payment system. Thus, this thesis proposes a Sustainable Federated Byzantine Agreement (SFBA) to deal with these problems. First, SFBA proposes an effective slice selection algorithm to significantly reduce the possibility of single point of failure. Then, SFBA utilizes the concept of majority of witness to achieve the consistency of global consensus and ensure system safety. The slice replacement and random witness selection successfully avoid the system dominance problem. Finally, the proposed slice rearrangement algorithm can automatically recover system from stuck and obtain stronger system liveness.
Based on the system analyses and simulation results, SFBA successfully guarantees the consistency of global consensus. Compared to Stellar, the participants of consensus procedure are highly diverse which prevents system from being dominated by few members. Finally, when lots of members malfunction, services of Stellar are apt to be interrupted. On the contrary, SFBA automatically discovers system stuck and then recovers it bringing stronger system liveness. Consequently, the proposed SFBA will be the most practical blockchain technology applied in payment systems for large-scale networks.

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