VOD (Video on Demand) 架構因為目前的影音分享平台愈來愈紅，雖然這是個成熟的平台，大家使用率也很高，但是我們覺得他還是有不足的地方。
Media streaming在傳輸過程中通常使用RTP (Rea-Time Streaming Protocol)協定，但是在目前的系統中傳送的過程並不具備安全加密的機制，所以我們為這個架構加入SRTP (Secure RTP)協定，使得streaming在傳輸過程中具備加密性與完整性。除了不具備安全的傳輸之外，我們還想說是不是可以為一個能力不足或是無法做改變的播放裝置 ，讓這種的裝置也可以做安全的傳輸。
所以我們提出一個位於大樓安全閘道器，命名為Building Security Gateway (BSG)，我們想讓BSG可以幫一些裝置做安全的傳輸，負責家庭或是企業安全傳輸。
實行SRTP之後，我們使用pre-shared key exchange與Diffie-Hellman key exchange兩種key交換作為SRTP master key交換機制。
有了基本的安全改善後，我們再加入media client向BSG註冊的機制。這個機制可以讓media client通知BSG，自己本身可不可以做安全的傳輸。如果media client可以做的話，BSG就會forward封包不處理；如果media client不能做的話，那BSG就會幫忙media client做加解密的動作。

In recent years, the platform of VOD (video on Demand) architecture is becoming more and more popular. It is widely used all over the world, but we make it better for lack of security.
RTP (Real-Time Streaming Protocol) is the protocol defined to sending media streaming. VOD use RTP to send media streaming so it lacks secure transmission. We add SRTP (Secure RTP) protocol in the VOD architecture to provide systems with encryption, message authentication and integrity. Besides that, we are going to create the device that can make it possible to help other devices which are weak processing or can’t do security processing secure.
We create the secure device named BSG (Building Security Gateway) to help other devices have secure transmission in home or enterprise use.
In addition, the key management is required. We use two key exchange mechanism, pre-shared key and Diffie-Hellman key exchange management for SRTP master key exchange.
With the improvement of basic security, we add the function of the media client registers to BSG. The media client will tell BSG whether it can transmit securely or not. BSG will forwards the packet without processing if the media client supports SRTP. However, BSG will help the media client transmit securely if the media client doesn’t support SRTP.

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