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vanced Ecryption Standard (AES) and the arcfour pseudorandom func-
tion. It uses up to 256-bit pseudorandom salt values and supports 48-byte passwords.
At a very high level, our basic ABE scheme is reminiscent of Yao\'s garbled circuits, with 4 gadgets per gate of the circuit, but where the decrypter in our scheme puts together the appropriate subset of gate gadgets like puzzle pieces by using a cryptographic multilinear map to multiply the pieces together. We use a novel twist of Waters\' dual encryption methodology to prove the full security of our scheme. Most importantly, we show how to preserve the delicate information-theoretic argument at the heart of Waters\' dual system by enfolding it in an information-theoretic argument similar to that used in Yao\'s garbled circuits.
The common interpretation of these negative results is that traditional privacy is impossible even with \"very structured\" imperfect sources. Somewhat surprisingly, Dodis et al. [DLMV12] put a slight dent in this belief, by showing that non-trivial *differential* privacy is possible with SV sources. This suggested a qualitative gap between traditional and differential privacy, and left open the question if differential privacy is possible with more realistic (i.e., less structured) sources than the SV sources. Motivated by solving this question, we abstract and generalize prior techniques for showing impossibility results for achieving privacy with various imperfect sources of randomness. In particular, we introduce the concepts of separability and expressivity of a given imperfect source as a measure of its \"imperfectness\", and show the
(1) Separability implies expressivity;
(2) Low levels of expressivity (and, thus, separability) generically imply strong impossibility results for both traditional and *differential* privacy;
(3) Existing (and quantitatively improved!) impossibility results for traditional privacy with respect to known imperfect sources easily follow as corollaries of our unified framework; New results follow equally easily.
(4) Although, unsurprisingly, our new impossibility results for differential privacy (barely) miss the highly structured SV sources, they come back *extremely quickly* once the source becomes slightly more realistic. E.g., if a small number of bits r_i can be fully determined by the previous bits;
(5) Any imperfect source allowing (either traditional or differential) privacy admits a certain type of deterministic bit extraction. (This result is incomparable to the result of [BD07].)
Overall, our results unify and strengthen the belief that, for the most part, privacy with imperfect randomness is impossible, unless the source is (almost) deterministically extractable.
This paper introduces a constant-round CB-PWS protocol which remains computationally efficient, compared to known CB-PWS systems. Our construction is comparable to similar solutions regarding users\' privacy.
and showed, as a negative result, that the existence of a computational ``secure sketch\'\'
implies the existence of an information-theoretically secure sketch with slightly weaker parameters.
In this work, we show a similar negative result such that, under some computational assumption,
the existence of a computational fuzzy extractor also implies the existence of
an information-theoretic fuzzy extractor with slightly weaker parameters.
The assumption is that the generation procedure of the fuzzy extractor can be efficiently invertible.
This result implies that to circumvent the limitations of information-theoretic fuzzy extractors,
we need to employ computational fuzzy extractors in which the generation procedure cannot be efficiently invertible.
about the correct, security and performance are also described. The experiment emulation and compare analysis suggest the feasibility and advantage.
In this paper we show how pairing-based group signature schemes (PB-GSSs) based on the sign-and-encrypt-and-prove (SEP) paradigm can be generically transformed in order to support one particular enhanced anonymity management mechanism, i.e., we propose a transformation that turns every such PB-GSS into a PB-GSS with controllable linkability. Basically, this transformation replaces the public key encryption scheme used for identity escrow within a group signature scheme with a modified all-or-nothing public key encryption with equality tests scheme (denoted AoN-PKEET$^*$) instantiated from the respective public key encryption scheme. Thereby, the respective trapdoor is given to the linking authority as a linking key. The appealing benefit of this approach in contrast to other anonymity management mechanisms (such as those provided by traceable signatures) is that controllable linkability can be added to PB-GSSs based on the SEP paradigm for free, i.e., it neither influences the signature size nor the computational costs for signers and verifiers in comparison to the scheme without this feature.