雲端儲存的應用日漸重要，上面存放著許多我們重要的資料。但當今沒有一個很有效率的檢驗機制，檢驗儲存中的檔案是否受到雲端儲存系統任意更動。並且當這些情況發生時，提供一個快速的流程來釐清責任，將這些情況公平的呈交並證明給公正方，像是法院，讓損失者可以得到應有的賠償。為了解決這樣的問題，我們提出「敏捷證明違約機制」。他是一個低負擔且高效率的系統，對客戶端和雲端都平等的設計。客戶端不再需要儲存任何檔案的雜湊值或其他資訊，而是藉由同步伺服器與其他主機分享兩個簡短的數值就能維護自身權益。雲端除了保存客戶端的檔案之外，也只需要維護我們所提出的資料結構 FBHTree，就能保證檔案的狀態。搭配了寫入與讀取的傳輸協定，當爭議發生時，讓彼此都無法對驗證結果有所推辭。效能方面，在相對於單純的檔案傳輸時間下，該系統客戶端從雲端讀取一個檔案，可以擁有幾乎同樣的速度，卻還能保證檔案的新鮮性。而客戶端向雲端寫入一個檔案，會從兩倍到同樣不等。小檔案 10Kb~10Mb 會有兩倍傳輸時間，而大於 10Mb 的檔案則有一樣的傳輸時間。

Cloud storage are getting popular and important now. We use them to conserve the files that are significant to us. But there still does not exist an efficient solution to detect and prove the consistency on those files, such as integrity, write in serial and read freshness. We do not want to read the files that out of latest version or got lost. It needs a procedure to clarify the responsibility between us and cloud storage when the disputes happen to us. And no one can repudiate the result. To fix the issue, we propose Real-time POV, which is light duty and fast way designed for client devices and cloud storage. Client devices have no need to cache any hash values of files or other information, but only two short values shared by synchronization server. Cloud storage also only need a small size of data structure, FBHTree, to maintain the attestation besides the files. With combining the protocol proposed in this paper, the system makes client devices have almost the same transaction time comparing to pure file transaction on reading a file from cloud storage for all the size on them. And 2 times higher when
writing small files, for example 100 Kb. But also having the same transaction time on bigger files, such as higher than 10Mb.

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