3,943 research outputs found
Parallel repetition for entangled k-player games via fast quantum search
We present two parallel repetition theorems for the entangled value of
multi-player, one-round free games (games where the inputs come from a product
distribution). Our first theorem shows that for a -player free game with
entangled value , the -fold repetition of
has entangled value at most , where is the answer length of any
player. In contrast, the best known parallel repetition theorem for the
classical value of two-player free games is , due to Barak, et al. (RANDOM 2009). This
suggests the possibility of a separation between the behavior of entangled and
classical free games under parallel repetition.
Our second theorem handles the broader class of free games where the
players can output (possibly entangled) quantum states. For such games, the
repeated entangled value is upper bounded by . We also show that the dependence of the exponent
on is necessary: we exhibit a -player free game and such
that .
Our analysis exploits the novel connection between communication protocols
and quantum parallel repetition, first explored by Chailloux and Scarpa (ICALP
2014). We demonstrate that better communication protocols yield better parallel
repetition theorems: our first theorem crucially uses a quantum search protocol
by Aaronson and Ambainis, which gives a quadratic speed-up for distributed
search problems. Finally, our results apply to a broader class of games than
were previously considered before; in particular, we obtain the first parallel
repetition theorem for entangled games involving more than two players, and for
games involving quantum outputs.Comment: This paper is a significantly revised version of arXiv:1411.1397,
which erroneously claimed strong parallel repetition for free entangled
games. Fixed author order to alphabetica
MPC for MPC: Secure Computation on a Massively Parallel Computing Architecture
Massively Parallel Computation (MPC) is a model of computation widely believed to best capture realistic parallel computing architectures such as large-scale MapReduce and Hadoop clusters. Motivated by the fact that many data analytics tasks performed on these platforms involve sensitive user data, we initiate the theoretical exploration of how to leverage MPC architectures to enable efficient, privacy-preserving computation over massive data. Clearly if a computation task does not lend itself to an efficient implementation on MPC even without security, then we cannot hope to compute it efficiently on MPC with security. We show, on the other hand, that any task that can be efficiently computed on MPC can also be securely computed with comparable efficiency. Specifically, we show the following results:
- any MPC algorithm can be compiled to a communication-oblivious counterpart while asymptotically preserving its round and space complexity, where communication-obliviousness ensures that any network intermediary observing the communication patterns learn no information about the secret inputs;
- assuming the existence of Fully Homomorphic Encryption with a suitable notion of compactness and other standard cryptographic assumptions, any MPC algorithm can be compiled to a secure counterpart that defends against an adversary who controls not only intermediate network routers but additionally up to 1/3 - ? fraction of machines (for an arbitrarily small constant ?) - moreover, this compilation preserves the round complexity tightly, and preserves the space complexity upto a multiplicative security parameter related blowup.
As an initial exploration of this important direction, our work suggests new definitions and proposes novel protocols that blend algorithmic and cryptographic techniques
Physical Randomness Extractors: Generating Random Numbers with Minimal Assumptions
How to generate provably true randomness with minimal assumptions? This
question is important not only for the efficiency and the security of
information processing, but also for understanding how extremely unpredictable
events are possible in Nature. All current solutions require special structures
in the initial source of randomness, or a certain independence relation among
two or more sources. Both types of assumptions are impossible to test and
difficult to guarantee in practice. Here we show how this fundamental limit can
be circumvented by extractors that base security on the validity of physical
laws and extract randomness from untrusted quantum devices. In conjunction with
the recent work of Miller and Shi (arXiv:1402:0489), our physical randomness
extractor uses just a single and general weak source, produces an arbitrarily
long and near-uniform output, with a close-to-optimal error, secure against
all-powerful quantum adversaries, and tolerating a constant level of
implementation imprecision. The source necessarily needs to be unpredictable to
the devices, but otherwise can even be known to the adversary.
Our central technical contribution, the Equivalence Lemma, provides a general
principle for proving composition security of untrusted-device protocols. It
implies that unbounded randomness expansion can be achieved simply by
cross-feeding any two expansion protocols. In particular, such an unbounded
expansion can be made robust, which is known for the first time. Another
significant implication is, it enables the secure randomness generation and key
distribution using public randomness, such as that broadcast by NIST's
Randomness Beacon. Our protocol also provides a method for refuting local
hidden variable theories under a weak assumption on the available randomness
for choosing the measurement settings.Comment: A substantial re-writing of V2, especially on model definitions. An
abstract model of robustness is added and the robustness claim in V2 is made
rigorous. Focuses on quantum-security. A future update is planned to address
non-signaling securit
Local Cyber-physical Attack with Leveraging Detection in Smart Grid
A well-designed attack in the power system can cause an initial failure and
then results in large-scale cascade failure. Several works have discussed power
system attack through false data injection, line-maintaining attack, and
line-removing attack. However, the existing methods need to continuously attack
the system for a long time, and, unfortunately, the performance cannot be
guaranteed if the system states vary. To overcome this issue, we consider a new
type of attack strategy called combinational attack which masks a line-outage
at one position but misleads the control center on line outage at another
position. Therefore, the topology information in the control center is
interfered by our attack. We also offer a procedure of selecting the vulnerable
lines of its kind. The proposed method can effectively and continuously deceive
the control center in identifying the actual position of line-outage. The
system under attack will be exposed to increasing risks as the attack
continuously. Simulation results validate the efficiency of the proposed attack
strategy.Comment: Accepted by IEEE SmartGridComm 201
王文興小說研究 : 從寫實、現代到後現代
王文興的小說自出版以來經常備受爭議,其中以《家變》最厲害,批評者的褒貶很極端,這種情況就好像西方現代主義文學作品在二十世紀初面世時所受的批評相似。筆者不想參與輕率褒貶的行列,而欲借用西方文學理論,加上台灣的社會文化背景來分析王文興的小說特色和發展,並且嘗試以新的角度細讀及賞析他的小說。本論文把王文興的《十五篇小說》、《家變》、《背海的人》上、下兩部順序分成三個階段,頭兩部小說各代表一個階段,《背海的人》上、下兩部代表最後一個階段。每章寫到一個階段的開始會個別分析每部小說的特色,然後分析每剖小說在王文興的小說創作中扮演的角色,從而尋找王文興小說的發展軌跡。由於王文興常被批評者視為現代主義者,閃此本論文將會分析他的小說與現代主義的關係,並且以此作為論文的主要內容。最後,本論文會總結以上四本小說的共同特徵,然後借用詹明信(Fredric Jameson)的理論來看它們的發展模式,並且提出現代主義以外的看法
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