Abstract: We investigate new strong security notions for on-line symmetric encryption schemes. We define the strongest achievable notion of privacy which takes into account both chosen-ciphertext attacks and the recently introduced blockwise-adaptive attacks. We show that all the schemes previously shown to be secure against blockwise-adaptive chosen-plaintext attacks are subject to blockwise-adaptive chosen-ciphertext attacks. We present an on-line encryption scheme that is provably secure under our notion. It uses any strong on-line cipher, the primitive we introduced Bellare, Boldyreva, Knudsen and Namprempre. Finally, we discuss the notion of authenticated on-line schemes and provide a secure construction.
Ref: A preliminary version of this paper is to appear in Proceedings of CT-RSA 2004 Conference, Lecture Notes in Computer Science, Springer-Verlag, 2004. Full paper available below.
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