現今人們大量使用網站所提供的網路服務用來與朋友互動以增進感情，透過秀出自己目前動態、觀察別人動態和利用文字訊息做即時交流。大多數網站所提供的網路服務必須在使用前先註冊帳號並填上個人基本資料，這會產生某些不肖業者盜賣用戶基本資料，類似事件層出不窮。另外這些使用者透過網站所提供的訊息交換系統(類似聊天室)，與朋友進行即時通訊，而這些訊息都儲存在社群網站的伺服器當中，此種儲存方式容易被有心人士監聽，甚至被政府所監視。而個人動態、文字訊息儲存在中央伺服器中也具有另一種風險，例如當中央伺服器因某些因素而造成當機，會使得個人動態、文字訊息等資料遺失，更嚴重可能使整個系統無法運作，這會讓使用者對系統失去信心進而產生大量的顧客流失率。
這些個人動態、文字訊息的資料量隨著時間和網站使用人數的增加而遞增，使資訊科技業進入下一個時代”海量資料”。在海量資料的時代裡，一個系統可能具有數億或數十億筆紀錄、數千到數萬個使用者和Petabytes/ Exabyte的資料量。此篇論文提出一套系統，利用RSA加密演算法的方法將個人動態或文字訊息給特定人士以增加個人隱私性和資料安全性。此外我們將此系統建立在P2P網路上以提升系統之可用性，防止單一伺服器失效而造成系統無法使用的情形。另外我們透過賭徒理論計算每筆記錄的備份數量使每項紀錄都可達到使用者所設定之可用性。
關鍵字：網路服務、海量資料、RSA加密演算法、P2P、賭徒理論、可用性

Nowadays, websites supply people with web service to express their own feelings and promote the relationship between themselves and their friends. The web service includes showing people’s current status, observing someone’s status and instant messaging online. Before users use the web service, they need to fill in their personal information for registration and this may cause user’s private information being stolen and sold by some unscrupulous traders. Besides, when users are using message exchange service provided by the website to communicate with their friends, these message records may be spied by a person with some purposes or monitored by government because all the text is stored in center server insecurely. Storing current status of users and message records in center serve will also trigger another problem; for example, center server may be crashed due to some unknown factors which will cause the loss of user’s current status or messages, and if all servers are crashed and the system is out of function, the churn occurs.
The numbers of users’ current status and message data will increase over time and numbers of register; Information Technology has ushered in a new era called “Big Data”. In Big Data, there may be thousands of users which will generate millions of records and copy Petabytes or Exabyte of replicas in big data era. This thesis proposes a system that uses RSA to encrypt users’ current status or messages and send to specific people. This system enhances users’ privacy and security; moreover, we build this system on P2P network in order to improve system availability and to avoid system crush caused by single user offline. Eventually, we use Gambler's Ruin to calculate the number of replica for each record to achieve data availability which is set by users.
Keywords: Web Service, Big Data, RSA, P2P, Gambler’s Ruin, Data Availability

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