9 research outputs found
A device-independent protocol for XOR oblivious transfer
Oblivious transfer is a cryptographic primitive where Alice has two bits and
Bob wishes to learn some function of them. Ideally, Alice should not learn
Bob's desired function choice and Bob should not learn any more than what is
logically implied by the function value. While decent quantum protocols for
this task are known, many become completely insecure if an adversary were to
control the quantum devices used in the implementation of the protocol. In this
work we give a fully device-independent quantum protocol for XOR oblivious
transfer.Comment: Accepted for publication in Quantum. Protocol modified to remove the
need for parties to send boxes to each other; new discussion section adde
Analytic quantum weak coin flipping protocols with arbitrarily small bias
Weak coin flipping (WCF) is a fundamental cryptographic primitive for
two-party secure computation, where two distrustful parties need to remotely
establish a shared random bit whilst having opposite preferred outcomes. It is
the strongest known primitive with arbitrarily close to perfect security
quantumly while classically, its security is completely compromised (unless one
makes further assumptions, such as computational hardness). A WCF protocol is
said to have bias if neither party can force their preferred outcome
with probability greater than . Classical WCF protocols are shown
to have bias , i.e., a cheating party can always force their preferred
outcome. On the other hand, there exist quantum WCF protocols with arbitrarily
small bias, as Mochon showed in his seminal work in 2007 [arXiv:0711.4114]. In
particular, he proved the existence of a family of WCF protocols approaching
bias for arbitrarily large and proposed a protocol
with bias . Last year, Arora, Roland and Weis presented a protocol with
bias and to go below this bias, they designed an algorithm that
numerically constructs unitary matrices corresponding to WCF protocols with
arbitrarily small bias [STOC'19, p.205-216]. In this work, we present new
techniques which yield a fully analytical construction of WCF protocols with
bias arbitrarily close to zero, thus achieving a solution that has been missing
for more than a decade. Furthermore, our new techniques lead to a simplified
proof of existence of WCF protocols by circumventing the non-constructive part
of Mochon's proof. As an example, we illustrate the construction of a WCF
protocol with bias .Comment: 13 + 14 pages, 3 figures; In v2, we give a new, simpler and shorter
solution. For further details and updates see
https://atulsingharora.github.io/WCF
Semi-device-independent quantum key distribution based on a coherence equality
We introduce the first example of a semi-device-independent quantum key
distribution (SDI-QKD) protocol with a classical Alice and Bob. The protocol is
based on the Coherence Equality (CE) game recently introduced by del Santo and
Daki\'c, which verifies a coherent quantum superposition of communication
trajectories in a de-localized way. We show the protocol to be
semi-device-independent since the only trusted operations occur in the users'
labs, and establish security against an adversary with bounded quantum memory.
Finally, we recast the setup of the protocol as a counterfactual test of
nonlocality, and provide additional insight into the CE game.Comment: 18 pages, 6 figure
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
Composably secure device-independent encryption with certified deletion
We study the task of encryption with certified deletion (ECD) introduced by
Broadbent and Islam (2019), but in a device-independent setting: we show that
it is possible to achieve this task even when the honest parties do not trust
their quantum devices. Moreover, we define security for the ECD task in a
composable manner and show that our ECD protocol satisfies conditions that lead
to composable security. Our protocol is based on device-independent quantum key
distribution (DIQKD), and in particular the parallel DIQKD protocol based on
the magic square non-local game, given by Jain, Miller and Shi (2020). To
achieve certified deletion, we use a property of the magic square game observed
by Fu and Miller (2017), namely that a two-round variant of the game can be
used to certify deletion of a single random bit. In order to achieve certified
deletion security for arbitrarily long messages from this property, we prove a
parallel repetition theorem for two-round non-local games, which may be of
independent interest.Comment: 46 pages, 2 figure
Device-independent uncloneable encryption
Uncloneable encryption, first introduced by Broadbent and Lord (TQC 2020) is
a quantum encryption scheme in which a quantum ciphertext cannot be distributed
between two non-communicating parties such that, given access to the decryption
key, both parties cannot learn the underlying plaintext. In this work, we
introduce a variant of uncloneable encryption in which several possible
decryption keys can decrypt a particular encryption, and the security
requirement is that two parties who receive independently generated decryption
keys cannot both learn the underlying ciphertext. We show that this variant of
uncloneable encryption can be achieved device-independently, i.e., without
trusting the quantum states and measurements used in the scheme, and that this
variant works just as well as the original definition in constructing quantum
money. Moreover, we show that a simple modification of our scheme yields a
single-decryptor encryption scheme, which was a related notion introduced by
Georgiou and Zhandry. In particular, the resulting single-decryptor encryption
scheme achieves device-independent security with respect to a standard
definition of security against random plaintexts. Finally, we derive an
"extractor" result for a two-adversary scenario, which in particular yields a
single-decryptor encryption scheme for single bit-messages that achieves
perfect anti-piracy security without needing the quantum random oracle model.Comment: Issue found in application of the extractor technique to uncloneable
encryption; corresponding claims have been removed. Added generalization of
our results to single-decryptor encryption, in which the extractor technique
can indeed be applie
Weak Coin Flipping in a Device-Independent Setting
A protocol is said to be device-independent when the level of its performance can be inferred without making any assumptions regarding the inner workings of the apparatus used to implement it. In this paper we introduce a device-independent weak coin flipping protocol based on a single GHZ test. Interestingly, the protocol calls for the exchange of (quantum) systems between participants; a feature which is not trivial to incorporate in a device-independent setting where a system's behavior may depend on the time, location, and its history. Alice's and Bob's maximal cheating probabilities are given by ≈ 0.974 and cos2 (π/ 8) ≈ 0.854. © 2014 Springer-Verlag Berlin Heidelberg.info:eu-repo/semantics/publishe