41,937 research outputs found
Multi-party Quantum Computation
We investigate definitions of and protocols for multi-party quantum computing
in the scenario where the secret data are quantum systems. We work in the
quantum information-theoretic model, where no assumptions are made on the
computational power of the adversary. For the slightly weaker task of
verifiable quantum secret sharing, we give a protocol which tolerates any t <
n/4 cheating parties (out of n). This is shown to be optimal. We use this new
tool to establish that any multi-party quantum computation can be securely
performed as long as the number of dishonest players is less than n/6.Comment: Masters Thesis. Based on Joint work with Claude Crepeau and Daniel
Gottesman. Full version is in preparatio
On the Communication Complexity of Secure Computation
Information theoretically secure multi-party computation (MPC) is a central
primitive of modern cryptography. However, relatively little is known about the
communication complexity of this primitive.
In this work, we develop powerful information theoretic tools to prove lower
bounds on the communication complexity of MPC. We restrict ourselves to a
3-party setting in order to bring out the power of these tools without
introducing too many complications. Our techniques include the use of a data
processing inequality for residual information - i.e., the gap between mutual
information and G\'acs-K\"orner common information, a new information
inequality for 3-party protocols, and the idea of distribution switching by
which lower bounds computed under certain worst-case scenarios can be shown to
apply for the general case.
Using these techniques we obtain tight bounds on communication complexity by
MPC protocols for various interesting functions. In particular, we show
concrete functions that have "communication-ideal" protocols, which achieve the
minimum communication simultaneously on all links in the network. Also, we
obtain the first explicit example of a function that incurs a higher
communication cost than the input length in the secure computation model of
Feige, Kilian and Naor (1994), who had shown that such functions exist. We also
show that our communication bounds imply tight lower bounds on the amount of
randomness required by MPC protocols for many interesting functions.Comment: 37 page
Quantum Private Comparison: A Review
As an important branch of quantum secure multiparty computation, quantum
private comparison (QPC) has attracted more and more attention recently. In
this paper, according to the quantum implementation mechanism that these
protocols used, we divide these protocols into three categories: The quantum
cryptography QPC, the superdense coding QPC, and the entanglement swapping QPC.
And then, a more in-depth analysis on the research progress, design idea, and
substantive characteristics of corresponding QPC categories is carried out,
respectively. Finally, the applications of QPC and quantum secure multi-party
computation issues are discussed and, in addition, three possible research
mainstream directions are pointed out
Scather: programming with multi-party computation and MapReduce
We present a prototype of a distributed computational infrastructure, an associated high level programming language, and an underlying formal framework that allow multiple parties to leverage their own cloud-based computational resources (capable of supporting MapReduce [27] operations) in concert with multi-party computation (MPC) to execute statistical analysis algorithms that have privacy-preserving properties. Our architecture allows a data analyst unfamiliar with MPC to: (1) author an analysis algorithm that is agnostic with regard to data privacy policies, (2) to use an automated process to derive algorithm implementation variants that have different privacy and performance properties, and (3) to compile those implementation variants so that they can be deployed on an infrastructures that allows computations to take place locally within each participantâs MapReduce cluster as well as across all the participantsâ clusters using an MPC protocol. We describe implementation details of the architecture, discuss and demonstrate how the formal framework enables the exploration of tradeoffs between the efficiency and privacy properties of an analysis algorithm, and present two example applications that illustrate how such an infrastructure can be utilized in practice.This work was supported in part by NSF Grants: #1430145, #1414119, #1347522, and #1012798
Separating Two-Round Secure Computation From Oblivious Transfer
We consider the question of minimizing the round complexity of protocols for secure multiparty computation (MPC) with security against an arbitrary number of semi-honest parties. Very recently, Garg and Srinivasan (Eurocrypt 2018) and Benhamouda and Lin (Eurocrypt 2018) constructed such 2-round MPC protocols from minimal assumptions. This was done by showing a round preserving reduction to the task of secure 2-party computation of the oblivious transfer functionality (OT). These constructions made a novel non-black-box use of the underlying OT protocol. The question remained whether this can be done by only making black-box use of 2-round OT. This is of theoretical and potentially also practical value as black-box use of primitives tends to lead to more efficient constructions.
Our main result proves that such a black-box construction is impossible, namely that non-black-box use of OT is necessary. As a corollary, a similar separation holds when starting with any 2-party functionality other than OT.
As a secondary contribution, we prove several additional results that further clarify the landscape of black-box MPC with minimal interaction. In particular, we complement the separation from 2-party functionalities by presenting a complete 4-party functionality, give evidence for the difficulty of ruling out a complete 3-party functionality and for the difficulty of ruling out black-box constructions of 3-round MPC from 2-round OT, and separate a relaxed "non-compact" variant of 2-party homomorphic secret sharing from 2-round OT
The Crypto-democracy and the Trustworthy
In the current architecture of the Internet, there is a strong asymmetry in
terms of power between the entities that gather and process personal data
(e.g., major Internet companies, telecom operators, cloud providers, ...) and
the individuals from which this personal data is issued. In particular,
individuals have no choice but to blindly trust that these entities will
respect their privacy and protect their personal data. In this position paper,
we address this issue by proposing an utopian crypto-democracy model based on
existing scientific achievements from the field of cryptography. More
precisely, our main objective is to show that cryptographic primitives,
including in particular secure multiparty computation, offer a practical
solution to protect privacy while minimizing the trust assumptions. In the
crypto-democracy envisioned, individuals do not have to trust a single physical
entity with their personal data but rather their data is distributed among
several institutions. Together these institutions form a virtual entity called
the Trustworthy that is responsible for the storage of this data but which can
also compute on it (provided first that all the institutions agree on this).
Finally, we also propose a realistic proof-of-concept of the Trustworthy, in
which the roles of institutions are played by universities. This
proof-of-concept would have an important impact in demonstrating the
possibilities offered by the crypto-democracy paradigm.Comment: DPM 201
From usability to secure computing and back again
Secure multi-party computation (MPC) allows multiple parties
to jointly compute the output of a function while preserving
the privacy of any individual partyâs inputs to that function.
As MPC protocols transition from research prototypes to realworld
applications, the usability of MPC-enabled applications
is increasingly critical to their successful deployment and
widespread adoption. Our Web-MPC platform, designed with
a focus on usability, has been deployed for privacy-preserving
data aggregation initiatives with the City of Boston and the
Greater Boston Chamber of Commerce. After building and
deploying an initial version of the platform, we conducted a
heuristic evaluation to identify usability improvements and
implemented corresponding application enhancements. However,
it is difficult to gauge the effectiveness of these changes
within the context of real-world deployments using traditional
web analytics tools without compromising the security guarantees
of the platform. This work consists of two contributions
that address this challenge: (1) the Web-MPC platform has
been extended with the capability to collect web analytics
using existing MPC protocols, and (2) as a test of this feature
and a way to inform future work, this capability has been
leveraged to conduct a usability study comparing the two versions
ofWeb-MPC. While many efforts have focused on ways
to enhance the usability of privacy-preserving technologies,
this study serves as a model for using a privacy-preserving
data-driven approach to evaluate and enhance the usability of
privacy-preserving websites and applications deployed in realworld
scenarios. Data collected in this study yields insights
into the relationship between usability and security; these can
help inform future implementations of MPC solutions.Published versio
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