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Using Trapdoor Permutations in a Complete Subtree Method for Broadcast Encryption
Ryo NOJIMA Yuichi KAJI
Publication
IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences
Vol.E88A
No.2
pp.568574 Publication Date: 2005/02/01 Online ISSN:
DOI: 10.1093/ietfec/e88a.2.568 Print ISSN: 09168508 Type of Manuscript: PAPER Category: Information Security Keyword: key management, broadcast encryption, stateless receivers, trapdoor permutations, clawfree permutations,
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Summary:
The complete subtree (CS) method is widely accepted for the broadcast encryption. A new method for assigning keys in the CS method is proposed in this paper. The essential idea behind the proposed method is to use two trapdoor permutations. Using the trapdoor information, the key management center computes and assigns a key to each terminal so that the terminal can derive all information necessary in the CS method. A terminal has to keep just one key, while log_{2} N + 1 keys were needed in the original CS method where N is the number of all terminals. The permutations to be used need to satisfy a certain property which is similar to but slightly different from the clawfree property. The needed property, named strongly semiclawfree property, is formalized in terms of probabilistic polynomial time algorithm, and its relation to the clawfree property is discussed. It is also shown that if the used permutations fulfill the strongly semiclawfree property, then the proposed method is secure against attacks of malicious users.

