安全群播金鑰管理之研究

Abstract

隨著網際網路的蓬勃發展，使得許多整合性的安全群組通訊(group communication)應用陸續透過網路來完成。安全群播(secure multicast)透過一有效率的方法將一相同通訊內容分送給所有的群組成員。然而為了達到通訊內容之機密性，一簡單的做法則是利用一對稱式金鑰來對通訊內容做加密。但是這可能會造成在金鑰更新(rekeying)時的負擔，尤其是面對一個龐大且動態的群組。過去一邏輯樹結構(tree-based)金鑰管理機制被廣泛地用來將金鑰更新時所產生的儲存、傳輸及計算成本降低至對數的群組成員人數。但要達到對數的金鑰更新成本的前題是要保持邏輯樹的平衡狀態。另一方面，邏輯樹結構金鑰管理機制可能會導致難以維持之同步性(synchronization)的問題。本論文提出了兩個應用於具延展性群播之金鑰管理機制來解決邏輯樹結構金鑰管理機制的問題並且獲得更佳的效能。首先，我們提出了一植基於機密分享之金鑰管理機制，利用一輕量化之前置式機密分享邏輯樹來解決金鑰邏輯樹所產生的問題。此外，我們消除了成員變動時所需之加解密過程，且金鑰可有效率地定期或是動態的更改。第二，我們提出了一以RSA為概念之群播金鑰管理機制來解決金鑰更新的問題。本研究提出了一星狀結構(star-based)來移除金鑰更新程序並且在群組成員變動時獲得比樹狀結構更好的效能。然而，我們亦將提供一延伸性的安全群播協定，在此我們將公開金鑰密碼系統和私密金鑰密碼系統結合起來達到更佳的執行效能。

The continuously growth of the Internet emerges many applications based on secure group communication. Secure multicast provides efficient delivery which includes an identical data from a source to multiple receivers. A common solution is to apply a symmetric key which is used to encrypt the transmitted data. However, the heavy cost of rekeying process is the main problem in large and dynamic multicast groups. The key tree-based architecture is widely used to reduce the rekeying cost of storage, transmission, and computation in the logarithm with the number of multicast group members. However, it usually requires extra overhead to keep key tree balance which is in order to achieve logarithmic rekeying cost. On the other hand, the key tree-based scheme may result in difficult problem to maintain synchronization due to the interdependencies among rekeying messages. Furthermore, we propose two key management schemes for scalable multicasting to solve the problem in the key tree-based schemes. First, we shall propose a key management scheme based on the secret sharing, in which we apply a new lightweight prepositioned secret sharing tree-based scheme to solve the problem in the key tree-based scheme. Furthermore, we eliminate the encryption/decryption processes during every membership and periodic key changes and can dynamically change the secret key frequently. Second, we shall propose a novel RSA-like multicast key management scheme to solve the rekeying problem. Our protocol applies a star-based architecture to eliminate the rekeying processes and provide the good performance in terms of membership changes in a multicast group. Furthermore, we also provide an extended secure multicast communication protocol, in which we combine public-key and symmetric-key cryptosystems to enhance the performance of multicast encryption.