3,012 research outputs found
Quantum Position Verification in the Random Oracle Model
Juhul kui kasutaja õigsuse kontrollimiseks on võimalik kasutada ainult tema asukohta, nimetatakse seda positsiooni verifitseerimiseks. Lihtsaim viis positsiooni verifitseerimisest on kasutaja kauguse mõõtmine keskpunktist (distance bounding). Verifitseerija paikneb kontrollitava ala keskel, saadab informatsiooni tõestajale ning kontrollib vastuse aega. Kuna selline ülesehitus ei ole alati soovitud, on võimalik kasutada ka teistsugust verifitseerijate asetust. Verifitseerijaid saab seada ümber tõestatava piirkonna, teatud liiki triangulatsioonis. Antud lõputöö muudab artiklis [Dominique Unruh, Quantum position verification in the random oracle model, CRYPTO 2014] esitatud positsiooni verifitseerimise protokolli, esitades uue versiooni protokollist, mis on turvaline väiksemal tõestataval piirkonnal. Algse protokolli\n\rturvalisuse tõestus kasutab kahe mängijaga põimunud kvantsüsteemide monogaamsuse mängu teoreemi. Lisades juurde ühe verifitseerija, defineerime uue kolme mängijaga põimunud kvantsüsteemide monogaamsuse mängu.\n\rTõestame et muudetud protokolli turvalisus sõltub uue kolme mängijaga mängu võidu tõenäosusest. Selgitame probleeme ja edusamme antud\n\rmonogaamsuse mängu tõestamisel. Võrdleme erinevaid kolme mängijaga monogaamsuse mänge ning tõestame mõned võidu tõenäosuste tulemused.Consider a situation where we wish to verify an entity solely by its location. This is called position verification. The simplest form of position verification is distance bounding where the verifier is located in the middle of the provers region, he sends information to the prover and checks how long it takes for the prover to respond. Since this is not always desirable one can place verifiers around the provers region forming a kind of triangulation. This thesis improves on the precision of the quantum position verification protocol form [Dominique Unruh, Quantum position verification in the random oracle model, CRYPTO 2014] i.e. presents a modification of the protocol that is sound for a smaller region. This is done by adding an additional receiving verifier. The previous result uses a two-player monogamy game. We define the three player monogamy game needed for the proof of the new protocol and explain our progress on the proof of this monogamy game. We also compare different three-player monogamy games and prove some results on their winning probabilities
Practically secure quantum position verification
We discuss quantum position verification (QPV) protocols in which the
verifiers create and send single-qubit states to the prover. QPV protocols
using single-qubit states are known to be insecure against adversaries that
share a small number of entangled qubits. We introduce QPV protocols that are
practically secure: they only require single-qubit states from each of the
verifiers, yet their security is broken if the adversaries share an
impractically large number of shared entangled qubits. These protocols are a
modification of known QPV protocols in which we include a classical random
oracle without altering the amount of quantum resources needed by the
verifiers. We present a cheating strategy that requires a number of entangled
qubits shared among the adversaries that grows exponentially with the size of
the classical input of the random oracle.Comment: v2: corrected errors, more detailed discussio
Quantum Cryptography Beyond Quantum Key Distribution
Quantum cryptography is the art and science of exploiting quantum mechanical
effects in order to perform cryptographic tasks. While the most well-known
example of this discipline is quantum key distribution (QKD), there exist many
other applications such as quantum money, randomness generation, secure two-
and multi-party computation and delegated quantum computation. Quantum
cryptography also studies the limitations and challenges resulting from quantum
adversaries---including the impossibility of quantum bit commitment, the
difficulty of quantum rewinding and the definition of quantum security models
for classical primitives. In this review article, aimed primarily at
cryptographers unfamiliar with the quantum world, we survey the area of
theoretical quantum cryptography, with an emphasis on the constructions and
limitations beyond the realm of QKD.Comment: 45 pages, over 245 reference
Making Existential-Unforgeable Signatures Strongly Unforgeable in the Quantum Random-Oracle Model
Strongly unforgeable signature schemes provide a more stringent security
guarantee than the standard existential unforgeability. It requires that not
only forging a signature on a new message is hard, it is infeasible as well to
produce a new signature on a message for which the adversary has seen valid
signatures before. Strongly unforgeable signatures are useful both in practice
and as a building block in many cryptographic constructions.
This work investigates a generic transformation that compiles any
existential-unforgeable scheme into a strongly unforgeable one, which was
proposed by Teranishi et al. and was proven in the classical random-oracle
model. Our main contribution is showing that the transformation also works
against quantum adversaries in the quantum random-oracle model. We develop
proof techniques such as adaptively programming a quantum random-oracle in a
new setting, which could be of independent interest. Applying the
transformation to an existential-unforgeable signature scheme due to Cash et
al., which can be shown to be quantum-secure assuming certain lattice problems
are hard for quantum computers, we get an efficient quantum-secure strongly
unforgeable signature scheme in the quantum random-oracle model.Comment: 15 pages, to appear in Proceedings TQC 201
The Quantum Query Complexity of Algebraic Properties
We present quantum query complexity bounds for testing algebraic properties.
For a set S and a binary operation on S, we consider the decision problem
whether is a semigroup or has an identity element. If S is a monoid, we
want to decide whether S is a group.
We present quantum algorithms for these problems that improve the best known
classical complexity bounds. In particular, we give the first application of
the new quantum random walk technique by Magniez, Nayak, Roland, and Santha
that improves the previous bounds by Ambainis and Szegedy. We also present
several lower bounds for testing algebraic properties.Comment: 13 pages, 0 figure
Quantum Lightning Never Strikes the Same State Twice
Public key quantum money can be seen as a version of the quantum no-cloning
theorem that holds even when the quantum states can be verified by the
adversary. In this work, investigate quantum lightning, a formalization of
"collision-free quantum money" defined by Lutomirski et al. [ICS'10], where
no-cloning holds even when the adversary herself generates the quantum state to
be cloned. We then study quantum money and quantum lightning, showing the
following results:
- We demonstrate the usefulness of quantum lightning by showing several
potential applications, such as generating random strings with a proof of
entropy, to completely decentralized cryptocurrency without a block-chain,
where transactions is instant and local.
- We give win-win results for quantum money/lightning, showing that either
signatures/hash functions/commitment schemes meet very strong recently proposed
notions of security, or they yield quantum money or lightning.
- We construct quantum lightning under the assumed multi-collision resistance
of random degree-2 systems of polynomials.
- We show that instantiating the quantum money scheme of Aaronson and
Christiano [STOC'12] with indistinguishability obfuscation that is secure
against quantum computers yields a secure quantum money schem
Quantum-secure message authentication via blind-unforgeability
Formulating and designing unforgeable authentication of classical messages in
the presence of quantum adversaries has been a challenge, as the familiar
classical notions of unforgeability do not directly translate into meaningful
notions in the quantum setting. A particular difficulty is how to fairly
capture the notion of "predicting an unqueried value" when the adversary can
query in quantum superposition. In this work, we uncover serious shortcomings
in existing approaches, and propose a new definition. We then support its
viability by a number of constructions and characterizations. Specifically, we
demonstrate a function which is secure according to the existing definition by
Boneh and Zhandry, but is clearly vulnerable to a quantum forgery attack,
whereby a query supported only on inputs that start with 0 divulges the value
of the function on an input that starts with 1. We then propose a new
definition, which we call "blind-unforgeability" (or BU.) This notion matches
"intuitive unpredictability" in all examples studied thus far. It defines a
function to be predictable if there exists an adversary which can use
"partially blinded" oracle access to predict values in the blinded region. Our
definition (BU) coincides with standard unpredictability (EUF-CMA) in the
classical-query setting. We show that quantum-secure pseudorandom functions are
BU-secure MACs. In addition, we show that BU satisfies a composition property
(Hash-and-MAC) using "Bernoulli-preserving" hash functions, a new notion which
may be of independent interest. Finally, we show that BU is amenable to
security reductions by giving a precise bound on the extent to which quantum
algorithms can deviate from their usual behavior due to the blinding in the BU
security experiment.Comment: 23+9 pages, v3: published version, with one theorem statement in the
summary of results correcte
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