Cryptology ePrint Archive: Report 2016/064

Unconditionally Secure Revocable Storage: Tight Bounds, Optimal Construction, and Robustness

Yohei Watanabe and Goichiro Hanaoka and Junji Shikata

Abstract: Data stored in cloud storage sometimes requires long-term security due to its sensitivity (e.g., genome data), and therefore, it also requires flexible access control for handling entities who can use the data. Broadcast encryption can partially provide such flexibility by specifying privileged receivers so that only they can decrypt a ciphertext. However, once privileged receivers are specified, they can be no longer dynamically added and/or removed. In this paper, we propose a new type of broadcast encryption which provides long-term security and appropriate access control, which we call unconditionally secure revocable-storage broadcast encryption (RS-BE). In RS-BE, privileged receivers of a ciphertext can be dynamically updated without revealing any information on the underlying plaintext. Specifically, we define a model and security of RS-BE, derive tight lower bounds on sizes of secret keys required for secure RS-BE, and propose a construction of RS-BE which meets all of these bounds. Our lower bounds can be applied to traditional broadcast encryption. Furthermore, to detect an improper update, we consider security against modification attacks to a ciphertext, and present a concrete construction secure against this type of attacks.

Category / Keywords: cryptographic protocols / Broadcast encryption, information-theoretic security, revocable storage, secret-key cryptography, unconditional security

Date: received 24 Jan 2016, last revised 25 Apr 2016

Contact author: watanabe at uec ac jp

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Version: 20160425:141434 (All versions of this report)

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