28,953 research outputs found
Optimal Probabilistic Ring Exploration by Asynchronous Oblivious Robots
We consider a team of identical, oblivious, asynchronous mobile robots
that are able to sense (\emph{i.e.}, view) their environment, yet are unable to
communicate, and evolve on a constrained path. Previous results in this weak
scenario show that initial symmetry yields high lower bounds when problems are
to be solved by \emph{deterministic} robots. In this paper, we initiate
research on probabilistic bounds and solutions in this context, and focus on
the \emph{exploration} problem of anonymous unoriented rings of any size. It is
known that robots are necessary and sufficient to solve the
problem with deterministic robots, provided that and are coprime.
By contrast, we show that \emph{four} identical probabilistic robots are
necessary and sufficient to solve the same problem, also removing the coprime
constraint. Our positive results are constructive
Unconditional security from noisy quantum storage
We consider the implementation of two-party cryptographic primitives based on
the sole assumption that no large-scale reliable quantum storage is available
to the cheating party. We construct novel protocols for oblivious transfer and
bit commitment, and prove that realistic noise levels provide security even
against the most general attack. Such unconditional results were previously
only known in the so-called bounded-storage model which is a special case of
our setting. Our protocols can be implemented with present-day hardware used
for quantum key distribution. In particular, no quantum storage is required for
the honest parties.Comment: 25 pages (IEEE two column), 13 figures, v4: published version (to
appear in IEEE Transactions on Information Theory), including bit wise
min-entropy sampling. however, for experimental purposes block sampling can
be much more convenient, please see v3 arxiv version if needed. See
arXiv:0911.2302 for a companion paper addressing aspects of a practical
implementation using block samplin
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