16 research outputs found
Can relativistic bit commitment lead to secure quantum oblivious transfer?
While unconditionally secure bit commitment (BC) is considered impossible
within the quantum framework, it can be obtained under relativistic or
experimental constraints. Here we study whether such BC can lead to secure
quantum oblivious transfer (QOT). The answer is not completely negative. On one
hand, we provide a detailed cheating strategy, showing that the
"honest-but-curious adversaries" in some of the existing no-go proofs on QOT
still apply even if secure BC is used, enabling the receiver to increase the
average reliability of the decoded value of the transferred bit. On the other
hand, it is also found that some other no-go proofs claiming that a dishonest
receiver can always decode all transferred bits simultaneously with reliability
100% become invalid in this scenario, because their models of cryptographic
protocols are too ideal to cover such a BC-based QOT.Comment: Published version. This paper generalized some results in Sec. V of
arXiv:1101.4587, and pointed out the limitation of the proof in
arXiv:quant-ph/961103
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
Quantum protocols for the millionaire problem with a third party are trivial
Recently there were many quantum protocols devoted to solve the millionaire
problem and private comparison problem by adding a semi-honest third party.
They all require complicated quantum methods, while still leak a non-trivial
amount of information to at least one of the parties. But it will be shown here
that once the third party is introduced, there are very simple protocols which
require quantum key distribution as the only quantum resource, and the amount
of information leaked can be made arbitrarily small. Furthermore, even a
dishonest third party cannot spoil the protocols. Thus our solutions surpass
all existing protocols on both feasibility and security.Comment: The protocol is further improved so that it remains secure even if
the third party is distrustfu
Contextual advantage for state discrimination
Finding quantitative aspects of quantum phenomena which cannot be explained
by any classical model has foundational importance for understanding the
boundary between classical and quantum theory. It also has practical
significance for identifying information processing tasks for which those
phenomena provide a quantum advantage. Using the framework of generalized
noncontextuality as our notion of classicality, we find one such nonclassical
feature within the phenomenology of quantum minimum error state discrimination.
Namely, we identify quantitative limits on the success probability for minimum
error state discrimination in any experiment described by a noncontextual
ontological model. These constraints constitute noncontextuality inequalities
that are violated by quantum theory, and this violation implies a quantum
advantage for state discrimination relative to noncontextual models.
Furthermore, our noncontextuality inequalities are robust to noise and are
operationally formulated, so that any experimental violation of the
inequalities is a witness of contextuality, independently of the validity of
quantum theory. Along the way, we introduce new methods for analyzing
noncontextuality scenarios, and demonstrate a tight connection between our
minimum error state discrimination scenario and a Bell scenario.Comment: 18 pages, 9 figure
Quantifying the Leakage of Quantum Protocols for Classical Two-Party Cryptography
We study quantum protocols among two distrustful parties. By adopting a
rather strict definition of correctness - guaranteeing that honest players
obtain their correct outcomes only - we can show that every strictly correct
quantum protocol implementing a non-trivial classical primitive necessarily
leaks information to a dishonest player. This extends known impossibility
results to all non-trivial primitives. We provide a framework for quantifying
this leakage and argue that leakage is a good measure for the privacy provided
to the players by a given protocol. Our framework also covers the case where
the two players are helped by a trusted third party. We show that despite the
help of a trusted third party, the players cannot amplify the cryptographic
power of any primitive. All our results hold even against quantum
honest-but-curious adversaries who honestly follow the protocol but purify
their actions and apply a different measurement at the end of the protocol. As
concrete examples, we establish lower bounds on the leakage of standard
universal two-party primitives such as oblivious transfer.Comment: 38 pages, completely supersedes arXiv:0902.403