17 research outputs found
Towards quantum-based privacy and voting
The privacy of communicating participants is often of paramount importance,
but in some situations it is an essential condition. A typical example is a
fair (secret) voting. We analyze in detail communication privacy based on
quantum resources, and we propose new quantum protocols. Possible
generalizations that would lead to voting schemes are discussed.Comment: 5 pages, improved description of the protoco
Quantum Private Information Retrieval with Sublinear Communication Complexity
This note presents a quantum protocol for private information retrieval, in
the single-server case and with information-theoretical privacy, that has
O(\sqrt{n})-qubit communication complexity, where n denotes the size of the
database. In comparison, it is known that any classical protocol must use
\Omega(n) bits of communication in this setting.Comment: 4 page
Interaction in Quantum Communication
In some scenarios there are ways of conveying information with many fewer,
even exponentially fewer, qubits than possible classically. Moreover, some of
these methods have a very simple structure--they involve only few message
exchanges between the communicating parties. It is therefore natural to ask
whether every classical protocol may be transformed to a ``simpler'' quantum
protocol--one that has similar efficiency, but uses fewer message exchanges.
We show that for any constant k, there is a problem such that its k+1 message
classical communication complexity is exponentially smaller than its k message
quantum communication complexity. This, in particular, proves a round hierarchy
theorem for quantum communication complexity, and implies, via a simple
reduction, an Omega(N^{1/k}) lower bound for k message quantum protocols for
Set Disjointness for constant k.
Enroute, we prove information-theoretic lemmas, and define a related measure
of correlation, the informational distance, that we believe may be of
significance in other contexts as well.Comment: 35 pages. Uses IEEEtran.cls, IEEEbib.bst. Submitted to IEEE
Transactions on Information Theory. Strengthens results in quant-ph/0005106,
quant-ph/0004100 and an earlier version presented in STOC 200
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
On the power of two-party quantum cryptography
We study quantum protocols among two distrustful parties. Under the
sole assumption of correctness - guaranteeing that honest players
obtain their correct outcomes - we show that every protocol
implementing a non-trivial 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