175,281 research outputs found
Perfect Secure Computation in Two Rounds
We show that any multi-party functionality can be evaluated using a two-round protocol with perfect correctness and perfect semi-honest security, provided that the majority of parties are honest. This settles the round complexity of information-theoretic semi-honest MPC, resolving a longstanding open question (cf. Ishai and Kushilevitz, FOCS 2000). The protocol is efficient for functionalities. Furthermore, given black-box access to a one-way function, the protocol can be made efficient for any polynomial functionality, at the cost of only guaranteeing computational security.
Our results are based on a new notion of \emph{multi-party randomized encoding} which extends and relaxes the standard notion of randomized encoding of functions (Ishai and Kushilevitz, FOCS 2000). The property of a multi-party randomized encoding (MPRE) is that if the functionality is an encoding of the functionality , then for any (permitted) coalition of players, their respective outputs and inputs in allow them to simulate their respective inputs and outputs in , without learning anything else, including the other outputs of . We further introduce a new notion of effective algebraic degree, and show that the round complexity of a functionality is characterized by the degree of its MPRE. We construct degree-2 MPREs for general functionalities in several settings under different assumptions, and use these constructions to obtain two-round protocols. Our constructions also give rise to new protocols in the client-server model with optimal round complexity
Violation of Bell's inequality: criterion for quantum communication complexity advantage
We prove that for every Bell's inequality and for a broad class of protocols,
there always exists a multi-party communication complexity problem, for which
the protocol assisted by states which violate the inequality is more efficient
than any classical protocol. Moreover, for that advantage Bell's inequality
violation is a necessary and sufficient criterion. Thus, violation of Bell's
inequalities has a significance beyond that of a non-optimal-witness of
non-separability.Comment: 4 pages, 1 figur
Non-adaptive Measurement-based Quantum Computation and Multi-party Bell Inequalities
Quantum correlations exhibit behaviour that cannot be resolved with a local
hidden variable picture of the world. In quantum information, they are also
used as resources for information processing tasks, such as Measurement-based
Quantum Computation (MQC). In MQC, universal quantum computation can be
achieved via adaptive measurements on a suitable entangled resource state. In
this paper, we look at a version of MQC in which we remove the adaptivity of
measurements and aim to understand what computational abilities still remain in
the resource. We show that there are explicit connections between this model of
computation and the question of non-classicality in quantum correlations. We
demonstrate this by focussing on deterministic computation of Boolean
functions, in which natural generalisations of the Greenberger-Horne-Zeilinger
(GHZ) paradox emerge; we then explore probabilistic computation, via which
multipartite Bell Inequalities can be defined. We use this correspondence to
define families of multi-party Bell inequalities, which we show to have a
number of interesting contrasting properties.Comment: 13 pages, 4 figures, final version accepted for publicatio
On Communication Protocols that Compute Almost Privately
A traditionally desired goal when designing auction mechanisms is incentive
compatibility, i.e., ensuring that bidders fare best by truthfully reporting
their preferences. A complementary goal, which has, thus far, received
significantly less attention, is to preserve privacy, i.e., to ensure that
bidders reveal no more information than necessary. We further investigate and
generalize the approximate privacy model for two-party communication recently
introduced by Feigenbaum et al.[8]. We explore the privacy properties of a
natural class of communication protocols that we refer to as "dissection
protocols". Dissection protocols include, among others, the bisection auction
in [9,10] and the bisection protocol for the millionaires problem in [8].
Informally, in a dissection protocol the communicating parties are restricted
to answering simple questions of the form "Is your input between the values
\alpha and \beta (under a predefined order over the possible inputs)?".
We prove that for a large class of functions, called tiling functions, which
include the 2nd-price Vickrey auction, there always exists a dissection
protocol that provides a constant average-case privacy approximation ratio for
uniform or "almost uniform" probability distributions over inputs. To establish
this result we present an interesting connection between the approximate
privacy framework and basic concepts in computational geometry. We show that
such a good privacy approximation ratio for tiling functions does not, in
general, exist in the worst case. We also discuss extensions of the basic setup
to more than two parties and to non-tiling functions, and provide calculations
of privacy approximation ratios for two functions of interest.Comment: to appear in Theoretical Computer Science (series A
Non-classicality of temporal correlations
The results of space-like separated measurements are independent of distant
measurement settings, a property one might call two-way no-signalling. In
contrast, time-like separated measurements are only one-way no-signalling since
the past is independent of the future but not vice-versa. For this reason
temporal correlations that are formally identical to non-classical spatial
correlations can still be modelled classically. We define non-classical
temporal correlations as the ones which cannot be simulated by propagating in
time a classical information content of a quantum system. We first show that
temporal correlations between results of any projective quantum measurements on
a qubit can be simulated classically. Then we present a sequence of POVM
measurements on a single -level quantum system that cannot be explained by
propagating in time -level classical system and using classical computers
with unlimited memory.Comment: 6 pages, 1 figur
Resolving Multi-party Privacy Conflicts in Social Media
Items shared through Social Media may affect more than one user's privacy ---
e.g., photos that depict multiple users, comments that mention multiple users,
events in which multiple users are invited, etc. The lack of multi-party
privacy management support in current mainstream Social Media infrastructures
makes users unable to appropriately control to whom these items are actually
shared or not. Computational mechanisms that are able to merge the privacy
preferences of multiple users into a single policy for an item can help solve
this problem. However, merging multiple users' privacy preferences is not an
easy task, because privacy preferences may conflict, so methods to resolve
conflicts are needed. Moreover, these methods need to consider how users' would
actually reach an agreement about a solution to the conflict in order to
propose solutions that can be acceptable by all of the users affected by the
item to be shared. Current approaches are either too demanding or only consider
fixed ways of aggregating privacy preferences. In this paper, we propose the
first computational mechanism to resolve conflicts for multi-party privacy
management in Social Media that is able to adapt to different situations by
modelling the concessions that users make to reach a solution to the conflicts.
We also present results of a user study in which our proposed mechanism
outperformed other existing approaches in terms of how many times each approach
matched users' behaviour.Comment: Authors' version of the paper accepted for publication at IEEE
Transactions on Knowledge and Data Engineering, IEEE Transactions on
Knowledge and Data Engineering, 201
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