由於現代網路的普及下，通訊軟體已是現代人使用率最高的軟體，但是在眾多琳琅滿目的通訊軟體中，我們要如何作出選擇呢？
本研究認為在使用者的隱私權的考量下，首先篩選掉使用Server-Client架構的通訊軟體，並以目前較為常見的點對點(P2P)通訊軟體並列出了幾項評比條件。像是否支援P2P加密、分散式儲存、開放程式碼、身份驗證、離線傳訊…等，經過分析後發現這些P2P通訊軟體尚有許多不足之處，這些不足處除了皆無法支援離線傳訊外，甚至可能訊息內容容易被外界審查。
因此本論文提出了幾個目標，主要是改善這些不足之處。在訊息傳送中使用了Diffie-Hellman加密技術，主要原因是Diffie-Hellman可以讓雙方在不安全的網路下建立一個安全的對稱金鑰，使用對稱金鑰加密後可以確保訊息在傳送過程中或分散式儲存在各個節點時，僅只有雙方才可以解密。儲存技術上則選擇了星際檔案系統(IPFS)架構，不僅是IPFS提供了P2P網路技術以及分散儲存技術外，同時為了推廣IPFS也提供了API方便使用者開發應用。
本論文實作出FreeChat通訊軟體來實現論文的研究目的，經過數個實驗驗證後，也證實了FreeChat可藉由IPFS架構達到離線/即時傳訊的功能。

Due to the popularity of the Internet, communication software has become the most commonly used software for people. However, among the numerous communication software, how do we choose?
This thesis believes that in the case of considering user privacy, server-client communication software is excluded. Some evaluation conditions are considered, e.g., whether it supports P2P encryption, distributed storage, open source, identity authentication, off-line messaging, and so on. After thorough investigation, it is found that the existing common P2P communication software would not support offline messages, and even the content of the messages is easily censored.
This thesis puts forward several goals, mainly to improve these shortcomings. The Diffie-Hellman encryption technology is used in message transmission. The main reason is that Diffie-Hellman allows both parties to establish a secure symmetric key under an insecure network. After using symmetric key encryption, the message can be ensured during transmission. Furthermore, when it is stored in various nodes in a distributed manner, only the communicating parties can decrypt it. In terms of storage technology, the IPFS(InterPlanetary File System) architecture was chosen. IPFS not only provides P2P network technology and distributed storage technology, but also provides API to facilitate users to develop applications.
In order to achieve the research purpose of the thesis, the FreeChat communication software was developed. After various experimental designs and verifications, Freechat can implement off-line/real-time messaging transmission functions through the IPFS architecture.

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