4,633 research outputs found
Perfectly Secure Index Coding
In this paper, we investigate the index coding problem in the presence of an
eavesdropper. Messages are to be sent from one transmitter to a number of
legitimate receivers who have side information about the messages, and share a
set of secret keys with the transmitter. We assume perfect secrecy, meaning
that the eavesdropper should not be able to retrieve any information about the
message set. We study the minimum key lengths for zero-error and perfectly
secure index coding problem. On one hand, this problem is a generalization of
the index coding problem (and thus a difficult one). On the other hand, it is a
generalization of the Shannon's cipher system. We show that a generalization of
Shannon's one-time pad strategy is optimal up to a multiplicative constant,
meaning that it obtains the entire boundary of the cone formed by looking at
the secure rate region from the origin. Finally, we consider relaxation of the
perfect secrecy and zero-error constraints to weak secrecy and asymptotically
vanishing probability of error, and provide a secure version of the result,
obtained by Langberg and Effros, on the equivalence of zero-error and
-error regions in the conventional index coding problem.Comment: 25 pages, 5 figures, submitted to the IEEE Transactions on
Information Theor
Timed Automata Semantics for Analyzing Creol
We give a real-time semantics for the concurrent, object-oriented modeling
language Creol, by mapping Creol processes to a network of timed automata. We
can use our semantics to verify real time properties of Creol objects, in
particular to see whether processes can be scheduled correctly and meet their
end-to-end deadlines. Real-time Creol can be useful for analyzing, for
instance, abstract models of multi-core embedded systems. We show how analysis
can be done in Uppaal.Comment: In Proceedings FOCLASA 2010, arXiv:1007.499
On The Positive Definiteness of Polarity Coincidence Correlation Coefficient Matrix
Polarity coincidence correlator (PCC), when used to estimate the covariance
matrix on an element-by-element basis, may not yield a positive semi-definite
(PSD) estimate. Devlin et al. [1], claimed that element-wise PCC is not
guaranteed to be PSD in dimensions p>3 for real signals. However, no
justification or proof was available on this issue. In this letter, it is
proved that for real signals with p<=3 and for complex signals with p<=2, a PSD
estimate is guaranteed. Counterexamples are presented for higher dimensions
which yield invalid covariance estimates.Comment: IEEE Signal Processing Letters, Volume 15, pp. 73-76, 200
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