自從比特幣2008年問世以來，區塊鏈就漸漸成為眾人所討論的對象，但因其做為一個金流交易平台，其運行的速度遠遠不及傳統金流平台如PayPal及Visa，使得區塊鏈雖然存在已超過10年，仍然只有極少數人將其視為日常交易的手段。因區塊鏈運行效率低落，促使了在改善區塊鏈交易速度方面的研究，而在此領域中，狀態通道特別受到矚目，因為其將區塊鏈的任務拆份，將對速度的要求轉移到區塊鏈之外，使得區塊鏈本身能夠更加專注於安全性及去中心化特性。
本篇論文利用智能合約建立狀態通道將大部分交易移至區塊鏈外，並在不違反虛擬狀態通道中的安全特性下，利用廣播策略加速虛擬狀態通道的建立，並使用領導人選舉的方式確保節點在執行時能夠與對方保持資料一致，以解決可能的競爭危害以及死結問題。
根據實驗結果，利用廣播策略在不同長度的虛擬狀態通道中平均有一倍以上的效能提升，並且使用非同步執行時，能夠再度增加節點約50%的吞吐量，並在最後的實驗證明了在現今區塊鏈系統中，以虛擬狀態通道取代狀態通道仍有一定的時間優勢。

Since Bitcoin first invented in 2008, blockchains has gradually gain public attention. However, as a global payment infrastructure, Bitcoin is extremely slow comparing to traditional payment service such as PayPal and Visa. Even today, more than 10 years since the existence of Bitcoin, only a minority of people use it as a daily payment method. Because blockchains are inefficient in terms of speed, how to speed up blockchains are a popular research area. Among these solutions, state channels are most promising one. Because state channels move scalability issue out of blockchain, make it possible to execute most of the transactions outside of it. State channels also help blockchains to focus on their security and decentralization characteristic.
In this paper, we propose a broadcast strategy to speed up the construction process of virtual state channel that build upon state channels by using smart contracts. Moreover, we use leader election method to ensure data consistency between two nodes, in order to solve possible deadlock and race condition situation without breaking the security characteristic of virtual state channel.
According to our experiment result, in variety length, broadcast strategy yield more than two times speedup in average, we also achieve 50% speedup in terms of throughput when using asynchronous operation, and prove that it is beneficial to replace state channels with virtual state channels in today’s blockchain system.

Chapter 1. 介紹--------------------------------------1
Chapter 2. 背景知識----------------------------------4
2.1. 提升區塊鏈交易速度----------------4
2.2. 智能合約與多重簽名錢包------------7
2.3. 狀態通道與建立--------------------8
2.4. 爭議的解決辦法-------------------11
2.5. 虛擬狀態通道---------------------12
2.6. 虛擬狀態通道中的簽名-------------15
2.7. 虛擬狀態通道建立步驟-------------16
Chapter 3. 觀察與動機-------------------------------17
3.1. 交換方式不夠有效-----------------17
3.2. 虛擬狀態通道的簽名交換順序-------19
3.3. 狀態通道鎖定時間過長-------------22
Chapter 4. 研究方法---------------------------------23
4.1. 廣播策略-------------------------23
4.2. 異步執行-------------------------25
Chapter 5. 實驗結果---------------------------------30
5.1. 實驗環境-------------------------30
5.2. 實驗結果-------------------------33
5.2.1 廣播策略-------------------------33
5.2.2 非同步執行-----------------------34
5.2.3 狀態通道與虛擬狀態通道時間比較---35
Chapter 6. 結論與未來研究方向-----------------------39
Reference------------------------------------------------40

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