587 research outputs found
Truthful Mechanisms for Agents that Value Privacy
Recent work has constructed economic mechanisms that are both truthful and
differentially private. In these mechanisms, privacy is treated separately from
the truthfulness; it is not incorporated in players' utility functions (and
doing so has been shown to lead to non-truthfulness in some cases). In this
work, we propose a new, general way of modelling privacy in players' utility
functions. Specifically, we only assume that if an outcome has the property
that any report of player would have led to with approximately the same
probability, then has small privacy cost to player . We give three
mechanisms that are truthful with respect to our modelling of privacy: for an
election between two candidates, for a discrete version of the facility
location problem, and for a general social choice problem with discrete
utilities (via a VCG-like mechanism). As the number of players increases,
the social welfare achieved by our mechanisms approaches optimal (as a fraction
of )
Engagement and Likeability of Negative Messages on Facebook during Israel's 2013 Elections
To contribute to the mapping of negative campaigns effects, this study examines the engagement (shares and comments) and likeability (likes) effects of negative campaigning strategies on Facebook during Israel's 2013 elections. The analysis shows that attacks, contrasts, and responses to negative messages are highly shared and commented on, illustrating the engaging nature of negative campaigning in Israel. In terms of likeability, results were mixed, as responses to negative messages were more liked than other messages, but attacks and contrasts were not. The 20 most-liked posts were analyzed and responses of the leader of the religious party Habayit HaYehudi to alleged attacks against modern orthodoxy attracted likes in dramatic numbers, riling followers who objected to the growing tensions between religious and secular Jews in Israel. The study provides the first mapping of the effects of an online negative campaign in Israel and illuminates the relevance of its political and religious context, particularly Israel’s polarized multi-party system and religious, democratic nature.
Combining Asynchronous and Synchronous Byzantine Agreement: The Best of Both Worlds
In the problem of byzantine agreement (BA), a set of n parties wishes to agree
on a value v by jointly running a distributed protocol. The protocol is deemed
secure if it achieves this goal in spite of a malicious adversary that
corrupts a certain fraction of the parties and can make them behave in
arbitrarily malicious ways. Since its first formalization by Lamport et al.
(TOPLAS `82), the problem of BA has been extensively studied in the literature
under many different assumptions. One common way to classify protocols for BA
is by their synchrony and network assumptions. For example, some protocols
offer resilience against up to a one-half fraction of corrupted parties by
assuming a synchronized, but possibly slow network, in which parties share a
global clock and messages are guaranteed to arrive after a given time D. By
comparison, other protocols achieve much higher efficiency and work without
these assumptions, but can tolerate only a one-third fraction of corrupted
parties. A natural question is whether it is possible to combine protocols
from these two regimes to achieve the ``best of both worlds\u27\u27: protocols that
are both efficient and robust. In this work, we answer this question in the
affirmative. Concretely, we make the following contributions:
* We give the first generic compilers that combine BA protocols under
different network and synchrony assumptions and preserve both the efficiency
and robustness of their building blocks. Our constructions are simple and rely
solely on a secure signature scheme.
* We prove that our constructions achieve optimal corruption bounds.
* Finally, we give the first efficient protocol for (binary) asynchronous
byzantine agreement (ABA) which tolerates adaptive corruptions and matches the
communication complexity of the best protocols in the static case
Topology-Hiding Computation Beyond Logarithmic Diameter
A distributed computation in which nodes are connected by a partial communication graph is called \emph{topology-hiding} if it does not reveal information about the graph (beyond what is revealed by the output of the function). Previous results [Moran, Orlov, Richelson; TCC\u2715] have shown
that topology-hiding computation protocols exist for graphs of logarithmic diameter (in the number of nodes), but the feasibility question for
graphs of larger diameter was open even for very simple graphs such as chains, cycles and trees.
In this work, we take a step towards topology-hiding computation protocols for arbitrary graphs by constructing protocols that can be used in a large class of {\em large-diameter networks}, including cycles, trees and graphs with logarithmic \emph{circumference}. Our results use very different methods from [MOR15] and can be based on a standard assumption (such as DDH)
Both “Constitutively-active” and “Inactive” Gαi3 Mutants Interact with GIRK1/2 Heterotetramer
Deterministic History-Independent Strategies for Storing Information on Write-Once Memories
Motivated by the challenging task of designing ``secure\u27\u27 vote storage mechanisms, we study information storage mechanisms that operate in extremely hostile environments. In such environments, the majority of existing techniques for information storage and for security are susceptible to powerful adversarial attacks. We propose a mechanism for storing a set of at most elements from a large universe of size on write-once memories in a manner that does not reveal the insertion order of the elements. We consider a standard model for write-once memories, in which the memory is initialized to the all \u27s state, and the only operation allowed is flipping bits from to . Whereas previously known constructions were either inefficient (required memory), randomized, or employed cryptographic techniques which are unlikely to be available in hostile environments, we eliminate each of these undesirable properties. The total amount of memory used by the mechanism is linear in the number of stored elements and poly-logarithmic in the size of the universe of elements.
We also demonstrate a connection between secure vote storage mechanisms and one of the classical distributed computing problems: conflict resolution in multiple-access channels. By establishing a tight connection with the basic building block of our mechanism, we construct the first deterministic and non-adaptive conflict resolution algorithm whose running time is optimal up to poly-logarithmic factors
Topology-Hiding Computation
Secure Multi-party Computation (MPC) is one of the foundational achievements of modern cryptography,
allowing multiple, distrusting, parties to jointly compute a function of their inputs, while revealing nothing but the
output of the function. Following the seminal works of Yao and Goldreich, Micali and Wigderson and Ben-Or, Goldwasser and Wigderson,
the study of MPC has expanded to consider a wide variety of questions, including variants in the attack model,
underlying assumptions, complexity and composability of the resulting protocols.
One question that appears to have received very little attention, however, is that of MPC over an
underlying communication network whose structure is, in itself, sensitive information. This question, in addition to being
of pure theoretical interest, arises naturally in many contexts: designing privacy-preserving social-networks, private peer-to-peer computations,
vehicle-to-vehicle networks and the ``internet of things\u27\u27 are some of the examples.
In this paper, we initiate the study of ``topology-hiding computation\u27\u27 in the computational setting. We give formal definitions
in both simulation-based and indistinguishability-based flavors. We show that, even for fail-stop adversaries, there are some strong
impossibility results. Despite this, we show that protocols for topology-hiding computation can be constructed in the semi-honest
and fail-stop models, if we somewhat restrict the set of nodes the adversary may corrupt
An Optimally Fair Coin Toss
We address one of the foundational problems in cryptography: the bias of coin-flipping protocols. Coin-flipping protocols allow mutually distrustful parties to generate a common unbiased random bit, guaranteeing that even if one of the parties is malicious, it cannot significantly bias the output of the honest party. A classical result by Cleve [STOC \u2786] showed that for any two-party -round coin-flipping protocol there exists an efficient adversary that can bias the output of the honest party by . However, the best previously known protocol only guarantees bias, and the question of whether Cleve\u27s bound is tight has remained open for more than twenty years.
In this paper we establish the optimal trade-off between the round complexity and the bias of two-party coin-flipping protocols. Under standard assumptions (the existence of oblivious transfer), we show that Cleve\u27s lower bound is tight: we construct an -round protocol with bias
Topology-Hiding Computation on all Graphs
A distributed computation in which nodes are connected by a partial communication graph is called topology-hiding if it does not reveal information about the graph beyond what is revealed by the output of the function. Previous results have shown that topology-hiding computation protocols exist for graphs of constant degree and logarithmic diameter in the number of nodes [Moran-Orlov-Richelson, TCC\u2715; Hirt \etal, Crypto\u2716] as well as for other graph families, such as cycles, trees, and low circumference graphs [Akavia-Moran, Eurocrypt\u2717], but the feasibility question for general graphs was open.
In this work we positively resolve the above open problem: we prove that topology-hiding computation is feasible for all graphs under either the Decisional Diffie-Hellman or Quadratic-Residuosity assumption.
Our techniques employ random-walks to generate paths covering the graph, upon which we apply the Akavia-Moran topology-hiding broadcast for chain-graphs (paths). To prevent topology information revealed by the random-walk, we design multiple random-walks that, together, are locally identical to receiving at each round a message from each neighbors and sending back processed messages in a randomly permuted order
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