13,359 research outputs found
Forward Private Searchable Symmetric Encryption with Optimized I/O Efficiency
Recently, several practical attacks raised serious concerns over the security
of searchable encryption. The attacks have brought emphasis on forward privacy,
which is the key concept behind solutions to the adaptive leakage-exploiting
attacks, and will very likely to become mandatory in the design of new
searchable encryption schemes. For a long time, forward privacy implies
inefficiency and thus most existing searchable encryption schemes do not
support it. Very recently, Bost (CCS 2016) showed that forward privacy can be
obtained without inducing a large communication overhead. However, Bost's
scheme is constructed with a relatively inefficient public key cryptographic
primitive, and has a poor I/O performance. Both of the deficiencies
significantly hinder the practical efficiency of the scheme, and prevent it
from scaling to large data settings. To address the problems, we first present
FAST, which achieves forward privacy and the same communication efficiency as
Bost's scheme, but uses only symmetric cryptographic primitives. We then
present FASTIO, which retains all good properties of FAST, and further improves
I/O efficiency. We implemented the two schemes and compared their performance
with Bost's scheme. The experiment results show that both our schemes are
highly efficient, and FASTIO achieves a much better scalability due to its
optimized I/O
Limitations of Passive Protection of Quantum Information
The ability to protect quantum information from the effect of noise is one of
the major goals of quantum information processing. In this article, we study
limitations on the asymptotic stability of quantum information stored in
passive N-qubit systems. We consider the effect of small imperfections in the
implementation of the protecting Hamiltonian in the form of perturbations or
weak coupling to a ground state environment. We prove that, regardless of the
protecting Hamiltonian, there exists a perturbed evolution that necessitates a
final error correcting step when the state of the memory is read. Such an error
correction step is shown to require a finite error threshold, the lack thereof
being exemplified by the 3D compass model. We go on to present explicit weak
Hamiltonian perturbations which destroy the logical information stored in the
2D toric code in a time O(log(N)).Comment: 17 pages and appendice
Large Scale Hierarchical K-Means Based Image Retrieval With MapReduce
Image retrieval remains one of the most heavily researched areas in Computer Vision. Image retrieval methods have been used in autonomous vehicle localization research, object recognition applications, and commercially in projects such as Google Glass. Current methods for image retrieval become problematic when implemented on image datasets that can easily reach billions of images. In order to process these growing datasets, we distribute the necessary computation for image retrieval among a cluster of machines using Apache Hadoop. While there are many techniques for image retrieval, we focus on systems that use Hierarchical K-Means Trees. Successful image retrieval systems based on Hierarchical K-Means Trees have been built using the tree as a Visual Vocabulary to build an Inverted File Index and implementing a Bag of Words retrieval approach, or by building the tree as a Full Representation of every image in the database and implementing a K-Nearest Neighbor voting scheme for retrieval. Both approaches involve different levels of approximation, and each has strengths and weaknesses that must be weighed in accordance with the needs of the application. Both approaches are implemented with MapReduce, for the first time, and compared in terms of image retrieval precision, index creation run-time, and image retrieval throughput. Experiments that include up to 2 million images running on 20 virtual machines are shown
Topological quantum memory
We analyze surface codes, the topological quantum error-correcting codes
introduced by Kitaev. In these codes, qubits are arranged in a two-dimensional
array on a surface of nontrivial topology, and encoded quantum operations are
associated with nontrivial homology cycles of the surface. We formulate
protocols for error recovery, and study the efficacy of these protocols. An
order-disorder phase transition occurs in this system at a nonzero critical
value of the error rate; if the error rate is below the critical value (the
accuracy threshold), encoded information can be protected arbitrarily well in
the limit of a large code block. This phase transition can be accurately
modeled by a three-dimensional Z_2 lattice gauge theory with quenched disorder.
We estimate the accuracy threshold, assuming that all quantum gates are local,
that qubits can be measured rapidly, and that polynomial-size classical
computations can be executed instantaneously. We also devise a robust recovery
procedure that does not require measurement or fast classical processing;
however for this procedure the quantum gates are local only if the qubits are
arranged in four or more spatial dimensions. We discuss procedures for
encoding, measurement, and performing fault-tolerant universal quantum
computation with surface codes, and argue that these codes provide a promising
framework for quantum computing architectures.Comment: 39 pages, 21 figures, REVTe
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