2 research outputs found
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
Quantum key distribution based on orthogonal states allows secure quantum bit commitment
For more than a decade, it was believed that unconditionally secure quantum
bit commitment (QBC) is impossible. But basing on a previously proposed quantum
key distribution scheme using orthogonal states, here we build a QBC protocol
in which the density matrices of the quantum states encoding the commitment do
not satisfy a crucial condition on which the no-go proofs of QBC are based.
Thus the no-go proofs could be evaded. Our protocol is fault-tolerant and very
feasible with currently available technology. It reopens the venue for other
"post-cold-war" multi-party cryptographic protocols, e.g., quantum bit string
commitment and quantum strong coin tossing with an arbitrarily small bias. This
result also has a strong influence on the Clifton-Bub-Halvorson theorem which
suggests that quantum theory could be characterized in terms of
information-theoretic constraints.Comment: Published version plus an appendix showing how to defeat the
counterfactual attack, more references [76,77,90,118-120] cited, and other
minor change