A Distributed Key Assignment Protocol for Secure Multicast Based on Proxy Cryptography


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A secure multicast framework should only allow authorized members of a group to decrypt received messages; usually one “group key” is shared by all approved members. However, this raises the problem of “one affects all,” whereby the actions of one member affect the whole group. Many researchers solve the problem by dividing a group into several subgroups, but most existing solutions require a centralized trusted controller to coordinate cryptographic keys for subgroups. We believe this is a constraint on network scalability. In this paper, we propose a novel framework to solve key management problems in multicast networks. Our contribution is three-fold: 1) We exploit the ElGamal cryptosystem and propose the idea of key composition; 2) A distributed key assignment protocol is proposed to eliminate the need for a centralized trust controller in a secure multicast network that leverages proxy cryptography; and 3) We adopt a hybrid encryption technique that makes our framework more efficient and practical. Comparison with similar frameworks shows the proposed scheme is efficient in both time and space complexity. In addition, costs of most protocol operations are bounded by constants regardless of a group’s size and the degree of transit nodes.

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A Distributed Key Assignment Protocol for Secure Multicast Based on Proxy Cryptography

  1. 1. A Distribute Key Assignment Protocol for Secure Multicast Based on Proxy Cryptography Chun-Ying Huang, Yun-Peng Chiu, Kuan-Ta Chen, and Chin-Laung Lei Distributed Computing and Network Security Lab Department of Electrical Engineering National Taiwan University March 21, 2006 ASIACCS'06 1
  2. 2. Outline Secure Multicast Problem Statements and Assumptions Our Scheme March 21, 2006 ASIACCS'06 2
  3. 3. Secure Multicast The Goal Share common secrets between group members. Secure Multicast: Classifications and Problems Distributed Centralized Decentralized (Contributory) 1 1 1 8 2 8 2 8 2 A D 7 G 3 7 R 3 7 3 B C 6 4 6 4 6 4 5 5 5 Need a group controller. Scale better, however ... Need to know group Bad scalability. May still need a group members. controller. Bad for a large group. March 21, 2006 ASIACCS'06 3
  4. 4. The Problem Statement and Assumptions For a large communication group … It would be better to adopt “decentralized” mechanisms. However, we don’t like the group controller. Besides, we should only put limited trust on intermediate branch nodes. Our scheme is based on ElGamal proxy encryption It can be easily applied on a source-based multicast tree. It reduces the trust-level on intermediate nodes. Assumptions The sender and the receivers are trusted. Proxies are semi-trusted. March 21, 2006 ASIACCS'06 4
  5. 5. Our Scheme – Adopt Proxy Encryption Proxies are only semi-trusted Transform the cipher-text without revealing the message. March 21, 2006 ASIACCS'06 5
  6. 6. Our Scheme – Remove the Group Controller Basic Ideas The sender and the proxies generate their own secret keys. The receiver obtain the decryption key using the proposed key-composition protocol. March 21, 2006 ASIACCS'06 6
  7. 7. Thank You! Comments or Questions? March 21, 2006 ASIACCS'06 7