scholarly journals Randomness in nonlocal games between mistrustful players

2017 ◽  
Vol 17 (7&8) ◽  
pp. 595-610
Author(s):  
Carl A. Miller ◽  
Yaoyun Shi
Keyword(s):  
Quantum Cryptography ◽  
Cryptographic Protocols ◽  
Related Question ◽  
The Other ◽  
Signaling Game ◽  
Local Randomness ◽  
Quantum Strategies

If two quantum players at a nonlocal game G achieve a superclassical score, then their measurement outcomes must be at least partially random from the perspective of any third player. This is the basis for device-independent quantum cryptography. In this paper we address a related question: does a superclassical score at G guarantee that one player has created randomness from the perspective of the other player? We show that for complete-support games, the answer is yes: even if the second player is given the first player’s input at the conclusion of the game, he cannot perfectly recover her output. Thus some amount of local randomness (i.e., randomness possessed by only one player) is always obtained when randomness is certified from nonlocal games with quantum strategies. This is in contrast to non-signaling game strategies, which may produce global randomness without any local randomness. We discuss potential implications for cryptographic protocols between mistrustful parties.

Bell inequality for quNits with binary measurements

2003 ◽  
Vol 3 (2) ◽  
pp. 157-164
Author(s):  
H. Bechmann-Pasquinucci ◽  
N. Gisin
Keyword(s):  
Quantum Cryptography ◽  
Bell Inequality ◽  
The Other ◽  
Entangled State ◽  
Maximally Entangled State ◽  
Von Neumann ◽  
Chsh Inequality ◽  
Intermediate States ◽  
Von Neumann Measurements

We present a generalized Bell inequality for two entangled quNits. On one quNit the choice is between two standard von Neumann measurements, whereas for the other quNit there are N^2 different binary measurements. These binary measurements are related to the intermediate states known from eavesdropping in quantum cryptography. The maximum violation by \sqrt{N} is reached for the maximally entangled state. Moreover, for N=2 it coincides with the familiar CHSH-inequality.

scholarly journals Card-Based Cryptographic Logical Computations Using Private Operations

2020 ◽  
Author(s):  
Hibiki Ono ◽  
Yoshifumi Manabe
Keyword(s):  
Cryptographic Protocols ◽  
The Other ◽  
General Logic ◽  
Private Values ◽  
Minimum Number ◽  
Logic Functions ◽  
Logical Functions

Abstract This paper proposes new card-based cryptographic protocols to calculate logic functions with the minimum number of cards using private operations under the semi-honest model. Though various card-based cryptographic protocols were shown, the minimum number of cards used in the protocol has not been achieved yet for many problems. Operations executed by a player where the other players cannot see are called private operations. Private operations have been introduced in some protocols to solve a particular problem or to input private values. However, the effectiveness of introducing private operations to the calculation of general logic functions has not been considered. This paper introduces three new private operations: private random bisection cuts, private reverse cuts, and private reveals. With these three new operations, we show that all of AND, XOR, and copy protocols are achieved with the minimum number of cards by simple three-round protocols. This paper then shows a protocol to calculate any logical functions using these private operations. Next, we consider protocols with malicious players.

Increasing data security by data compression

2005 ◽  
Vol 42 (4) ◽  
pp. 343-353
Author(s):  
Tibor Nemetz ◽  
Pál Papp
Keyword(s):  
Data Compression ◽  
Data Security ◽  
Cryptographic Protocols ◽  
Point Of View ◽  
The Other ◽  
Negative Effects ◽  
Practical Point

We analyze the effect of data-compression on security of encryption both from theoretical and practical point of view. It is demonstrated that data-compression essentially improves the security of encryption, helps to overcome technical difficulties. On the other side, it makes crypt-analysis more difficult and causes extra problems. At present data-compression applied rarely and frequently defectively. We propose a method which eliminates the negative effects. Our aim is initiate data compression as an aid for data security. To this end we provide an overview of the most frequently used cryptographic protocols. A comparison with encryption software reveals that even the most frequently used protocols do not support encryption and compression.

Unbounded entanglement in nonlocal games

2015 ◽  
Vol 15 (15&16) ◽  
pp. 1317-1332
Author(s):  
Laura Mančinska ◽  
Thomas Vidick
Keyword(s):  
Quantum Entanglement ◽  
Finite Length ◽  
Success Probability ◽  
The Other ◽  
Entangled States ◽  
Entangled State ◽  
Local Dimension ◽  
Hardy's Paradox ◽  
First Time ◽  
Quantum Strategies

Quantum entanglement is known to provide a strong advantage in many two-party distributed tasks. We investigate the question of how much entanglement is needed to reach optimal performance. For the first time we show that there exists a purely classical scenario for which no finite amount of entanglement suffices. To this end we introduce a simple two-party nonlocal game H, inspired by Lucien Hardy’s paradox. In our game each player has only two possible questions and can provide bit strings of any finite length as answer. We exhibit a sequence of strategies which use entangled states in increasing dimension d and succeed with probability 1 − O(d−c ) for some c ≥ 0.13. On the other hand, we show that any strategy using an entangled state of local dimension d has success probability at most 1 − Ω(d−2 ). In addition, we show that any strategy restricted to producing answers in a set of cardinality at most d has success probability at most 1 − Ω(d−2 ). Finally, we generalize our construction to derive similar results starting from any game G with two questions per player and finite answers sets in which quantum strategies have an advantage.

Quantum Computer and Post-Quantum Cryptography

2021 ◽  
Vol 12 (4) ◽  
pp. 171-178
Author(s):  
S. А. Bukashkin ◽  
◽  
М. А. Cherepniov ◽  
Keyword(s):  
Quantum Cryptography ◽  
Quantum Computer ◽  
Quantum Algorithms ◽  
Cryptographic Protocols ◽  
Theory And Practice ◽  
Current State ◽  
Electronic Computers ◽  
Post Quantum Cryptography

An overview of the current state of the problem of building a quantum computer and its hypothetical use for breaking cryptographic protocols is presented. The necessary parameters are considered. An overview of existing quantum algorithms and post-quantum cryptographic protocols that are strong with respect to them is presented. The problem of constructing a quantum computer is considered in comparison with the development of the theory and practice of conventional mechanical and electronic computers. The results of contests on the topic of post-quantum cryptography are presented.

Illegal Contracts and Unjustified Enrichment

2000 ◽  
Vol 4 (1) ◽  
pp. 19-45
Author(s):  
Laura J Macgregor
Keyword(s):  
Related Question ◽  
The Other ◽  
Breach Of Contract ◽  
Unjustified Enrichment ◽  
Vexed Question

If a contract is treated as an illegal contract, the contracting parties are denied the contractual remedies which would normally be available to them on breach of contract. The contract may, however, have been partially performed. For example, one contracting party may have delivered goods and received no payment from the other contracting party. The availability of unjustified enrichment remedies in this type of situation has been a vexed question, not only in Scots law, but in many other jurisdictions. This article looks at the Scottish approach to the availability of enrichment remedies and also at the related question of whether it is possible for title to goods to pass under an illegal contract. The focus thereafter lies on options for reform, and, in particular, the use of legislative discretion.

Upward directedness of the Rudin-Keisler ordering of p-points

1990 ◽  
Vol 55 (2) ◽  
pp. 449-456
Author(s):  
Claude Laflamme
Keyword(s):  
Lower Bound ◽  
Upper Bound ◽  
Related Question ◽  
The Other ◽  
Other Hand ◽  
New Construction

It has been proven by Blass [1973] that any two P-points which have a P-point as a common upper bound in the Rudin-Keisler (RK) ordering necessarily have a common lower bound (necessarily a P-point). Hence two nonisomorphic Ramsey ultrafilters have neither a common lower nor a common upper bound which is a P-point. So in a model of CH for example (or MA, P(c),…), the RK ordering restricted to P-points is neither upward nor downward directed, since it is well known that nonisomorphic Ramsey ultrafilters exist in such models. On the other hand, we will see that in the model for “near coherence of filters” (NCF) produced by Blass and Shelah [1985], the RK ordering of P-points is upward, hence downward directed. This shows that the question of directedness of the RK ordering of P-points, upward or downward, cannot be decided in ZFC.There is a related question, asked by Blass in [1973], whether two P-points which have a common lower bound necessarily have a common upper bound which is a P-point. Our main result establishes the independence of this statement relative to ZFC. Its consistency will follow as soon as we show that the RK ordering of P-points is upward directed in the NCF model mentioned above, which we do in §2. But its independence will require a new construction, and will be given in §3.

scholarly journals Learning Theory and Heterogeneous Play in a Signaling-Game Experiment

2019 ◽  
Vol 11 (4) ◽  
pp. 186-215 ◽  
Author(s):  
Drew Fudenberg ◽  
Emanuel Vespa
Keyword(s):  
Learning Theory ◽  
The Other ◽  
Signaling Game ◽  
Learning In Games ◽  
Fixed Type

We study the effect of how types are assigned to participants in a signaling-game experiment. The sender has two actions, In and Out, and two types. In one treatment, types are i.i.d. in every period, and senders gather experience with both types. In the other, types are assigned once-and-for-all, and feedback is type specific. The theory of learning in games predicts that the non-Nash but self-confirming equilibrium where some fraction of types play Out can persist in the fixed-type treatment but not when types are i.i.d. Our results confirm that more senders do play Out in the fixed-type treatment. (JEL C92, D82, D83)

scholarly journals Intercept/resend and translucent attacks on the quantum key distribution protocol based on the pre- and post-selection effect

2021 ◽  
pp. 2150010
Author(s):  
Hiroo Azuma ◽  
Masashi Ban
Keyword(s):  
Quantum Cryptography ◽  
Quantum Channel ◽  
Quantum Key Distribution ◽  
Degrees Of Freedom ◽  
Selection Effect ◽  
Key Distribution ◽  
The Other ◽  
Current Paper ◽  
Secret Key ◽  
Quantum Key Distribution Protocol

We investigate the security against the intercept/resend and translucent attacks on the quantum key distribution protocol based on the pre- and post-selection effect. In 2001, Bub proposed the quantum cryptography scheme, which was an application of the so-called mean king’s problem. We evaluate a probability that legitimate users cannot detect eavesdropper’s malicious acts for Bub’s protocol. We also estimate a probability that the eavesdropper guesses right at the random secret key one of the legitimate users tries to share with the other one. From rigorous mathematical and numerical analyses, we conclude that Bub’s protocol is weaker than the Bennett–Brassard protocol of 1984 (BB84) against both the intercept/resend and translucent attacks. Because Bub’s protocol uses a two-way quantum channel, the analyses of its security are tough to accomplish. We refer to their technical points accurately in the current paper. For example, we impose some constraints upon the eavesdropper’s strategies in order to let their degrees of freedom be small.

scholarly journals Minimum Round Card-Based Cryptographic Protocols Using Private Operations

Cryptography ◽  
2021 ◽  
Vol 5 (3) ◽  
pp. 17
Author(s):  
Hibiki Ono ◽  
Yoshifumi Manabe
Keyword(s):  
Boolean Functions ◽  
Cryptographic Protocols ◽  
Secure Multiparty Computation ◽  
The Other ◽  
Multiparty Computation ◽  
Minimum Number

This paper shows new card-based cryptographic protocols with the minimum number of rounds, using private operations under the semi-honest model. Physical cards are used in card-based cryptographic protocols instead of computers to achieve secure multiparty computation. Operations that a player executes in a place where the other players cannot see are called private operations. Using three private operations—private random bisection cuts, private reverse cuts, and private reveals—the calculations of two variable Boolean functions and copy operations were realized with the minimum number of cards. Though the number of cards has been discussed, the efficiency of these protocols has not been discussed. This paper defines the number of rounds to evaluate the efficiency of the protocols, using private operations. Most of the meaningful calculations using private operations need at least two rounds. This paper presents a new two-round committed-input, committed-output logical XOR protocol, using four cards. Then, we show new two-round committed-input, committed-output logical AND and copy protocols, using six cards. Even if private reveal operations are not used, logical XOR, logical AND, and copy operations can be executed with the minimum number of rounds. Protocols for general n-variable Boolean functions and protocols that preserve an input are also shown. Lastly, protocols with asymmetric cards are shown.

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