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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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March 21, 2006 ASIACCS'06 1
A Distribute Key Assignment Protocol for Secure MulticastBased on Proxy Cryptography
Chun-Ying Huang, Yun-Peng Chiu, Kuan-Ta Chen, and Chin-Laung Lei
Distributed Computing and Network Security LabDepartment of Electrical EngineeringNational Taiwan University
March 21, 2006 ASIACCS'06 2
Outline
Secure MulticastProblem Statements and AssumptionsOur Scheme
March 21, 2006 ASIACCS'06 3
Secure Multicast
The GoalShare common secrets between group members.
Secure Multicast: Classifications and Problems
G7
5
1
3
6 4
8 2
R
8
6
2
4
7
5
1
3
A
D
C
B7
5
1
3
6 4
8 2
Centralized Decentralized Distributed(Contributory)
Need a group controller.Bad scalability.
Scale better, however ...May still need a group controller.
Need to know group members.Bad for a large group.
March 21, 2006 ASIACCS'06 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 encryptionIt can be easily applied on a source-based multicast tree.It reduces the trust-level on intermediate nodes.
AssumptionsThe sender and the receivers are trusted.Proxies are semi-trusted.
March 21, 2006 ASIACCS'06 5
Our Scheme –Adopt Proxy Encryption
Proxies are only semi-trustedTransform the cipher-text without revealing the message.
March 21, 2006 ASIACCS'06 6
Our Scheme –Remove the Group Controller
Basic IdeasThe sender and the proxies generate their own secret keys.The receiver obtain the decryption key using theproposed key-composition protocol.
March 21, 2006 ASIACCS'06 7
Thank You!
Comments or Questions?
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