The aim of this work is to examine the relation between the notions of semantic security and indistinguishability against chosen ciphertext attacks. For this purpose, a new security notion called nondividability is introduced independent of attack models, and is shown to be equivalent to each of the previous two notions. This implies the equivalence between semantic security and indistinguishability under any form of attack.
This paper examines classical privacy amplification using a universal family of hash functions. In quantum key distribution, the adversary's measurement can wait until the choice of hash functions is announced, and so the adversary's information may depend on the choice. Therefore the existing result on classical privacy amplification, which assumes the independence of the choice from the other random variables, is not applicable to this case. This paper provides a security proof of privacy amplification which is valid even when the adversary's information may depend on the choice of hash functions. The compression rate of the proposed privacy amplification can be taken to be the same as that of the existing one with an exponentially small loss in secrecy of a final key.
Scattered waves generated by interaction of a vortex ring and a shock wave are studied experimentally and theoretically. Acoustic pressure is detected by microphones. A polar diagram of the acoustic pressure (with respect to time) constructed from the detected signals shows the waves clearly and the angular distribution of the acoustic pressure is captured visually. Mechanism of noise generation is also investigated. Theoretical formulation for sound scattering by vortex ÿeld is applied to describe shock-vortex interaction. Forms of the waves generated by the interaction are calculated by using the velocity ÿeld of a typical incident spherical shock wave and compared with the experimental data. Sound scattering by the density inhomogeneity inside a vortex core is also estimated. Some characteristic features of the scattered waves are described.
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