3,132 research outputs found
Simple, near-optimal quantum protocols for die-rolling
Die-rolling is the cryptographic task where two mistrustful, remote parties
wish to generate a random -sided die-roll over a communication channel.
Optimal quantum protocols for this task have been given by Aharon and Silman
(New Journal of Physics, 2010) but are based on optimal weak coin-flipping
protocols which are currently very complicated and not very well understood. In
this paper, we first present very simple classical protocols for die-rolling
which have decent (and sometimes optimal) security which is in stark contrast
to coin-flipping, bit-commitment, oblivious transfer, and many other two-party
cryptographic primitives. We also present quantum protocols based on
integer-commitment, a generalization of bit-commitment, where one wishes to
commit to an integer. We analyze these protocols using semidefinite programming
and finally give protocols which are very close to Kitaev's lower bound for any
. Lastly, we briefly discuss an application of this work to the
quantum state discrimination problem.Comment: v2. Updated titl
Variable Bias Coin Tossing
Alice is a charismatic quantum cryptographer who believes her parties are
unmissable; Bob is a (relatively) glamorous string theorist who believes he is
an indispensable guest. To prevent possibly traumatic collisions of
self-perception and reality, their social code requires that decisions about
invitation or acceptance be made via a cryptographically secure variable bias
coin toss (VBCT). This generates a shared random bit by the toss of a coin
whose bias is secretly chosen, within a stipulated range, by one of the
parties; the other party learns only the random bit. Thus one party can
secretly influence the outcome, while both can save face by blaming any
negative decisions on bad luck.
We describe here some cryptographic VBCT protocols whose security is
guaranteed by quantum theory and the impossibility of superluminal signalling,
setting our results in the context of a general discussion of secure two-party
computation. We also briefly discuss other cryptographic applications of VBCT.Comment: 14 pages, minor correction
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Unconditionally secure relativistic multi-party biased coin flipping and die rolling.
We introduce relativistic multi-party biased die-rolling protocols, generalizing coin flipping to M ≥ 2 parties and to N ≥ 2 outcomes for any chosen outcome biases and show them unconditionally secure. Our results prove that the most general random secure multi-party computation, where all parties receive the output and there is no secret input by any party, can be implemented with unconditional security. Our protocols extend Kent's (Kent A. 1999 Phys. Rev. Lett. 83, 5382) two-party unbiased coin-flipping protocol, do not require any quantum communication, are practical to implement with current technology and to our knowledge are the first multi-party relativistic cryptographic protocols
Breaking barriers in two-party quantum cryptography via stochastic semidefinite programming
In the last two decades, there has been much effort in finding secure
protocols for two-party cryptographic tasks. It has since been discovered that
even with quantum mechanics, many such protocols are limited in their security
promises. In this work, we use stochastic selection, an idea from stochastic
programming, to circumvent such limitations. For example, we find a way to
switch between bit commitment, weak coin flipping, and oblivious transfer
protocols to improve their security. We also use stochastic selection to turn
trash into treasure yielding the first quantum protocol for Rabin oblivious
transfer.Comment: 42 pages, 2 figure
Impossibility of adversarial self-testing and secure sampling
Self-testing is the task where spatially separated Alice and Bob cooperate to
deduce the inner workings of untrusted quantum devices by interacting with them
in a classical manner. We examine the task above where Alice and Bob do not
trust each other which we call adversarial self-testing. We show that
adversarial self-testing implies secure sampling -- a task that we introduce
where mistrustful Alice and Bob wish to sample from a joint probability
distribution with the guarantee that an honest party's marginal is not biased.
By extending impossibility results in two-party quantum cryptography, we give a
simple proof that both of these tasks are impossible in all but trivial
settings.Comment: 6 pages, 3 Figure
Fidelity of Quantum Strategies with Applications to Cryptography
We introduce a definition of the fidelity function for multi-round quantum strategies, which we call the strategy fidelity, that is a generalization of the fidelity function for quantum states. We provide many interesting properties of the strategy fidelity including a Fuchs-van de Graaf relationship with the strategy norm. We illustrate an operational interpretation of the strategy fidelity in the spirit of Uhlmann\u27s Theorem and discuss its application to the security analysis of quantum protocols for interactive cryptographic tasks such as bit-commitment and oblivious string transfer. Our analysis is very general in the sense that the actions of the protocol need not be fully specified, which is in stark contrast to most other security proofs. Lastly, we provide a semidefinite programming formulation of the strategy fidelity
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