隨著網路蓬勃的發展，許多網路的應用服務接應而生，基於P2P架構的即時影音串流(live streaming)便是近年來非常熱門的應用之一，而在P2P live streaming system中，由於使用者的數量龐大，加密金鑰的更新不適合用對Server重新要求的方式，這種集中式的方法將會造成Server的負擔太重，成為系統中的嚴重負擔，取而代之的便是利用分散式的方式來更新加密金鑰，Server只需將加密金鑰的更新訊息散佈給系統中的少數節點，之後便能利用P2P的特性，來更新整個系統的加密金鑰。於是，我們希望提出一個比較完整的金鑰管理機制，確保更新訊息以及系統的安全性，只讓合法的使用者才能正確的更新加密金鑰。
在目前的研究當中，有許多關於Group Key Management的方法，但卻少有針對P2P live streaming system所設計的金鑰管理，我們即是針對這部份來提出一個適合應用在P2P live streaming system的金鑰管理方法，並且給予完善的安全性分析，希望藉此提供一個安全的即時影音串流環境。

With rapid development of the Internet, many applications of network services have been developed for better livings. In recent years, live media streaming based on P2P network structure is a popular application. With numerous users in P2P live streaming system, it is not an affordable way to request from server for the key updating information since the server becomes the bottleneck of the system. Therefore, we propose a novel distributed key management scheme. The server only needs to transmit the key updating information to a limited number of users. Hence, we exploit the characteristic of P2P network structure to distribute the key updating information hop by hop. In this way, it can reduce the task of the server. Furthermore, with the high churn rate of user joining and leaving, we design an efficient key management method that authenticates the security of information updating. In our proposed scheme, only legal users in the P2P live streaming system can update the key correctly. Security analysis shows that our proposed scheme can provide the security measure for the P2P live streaming system even in a high churn rate of users.

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