We discuss the different ways of defining channel capacity for certain types of illicit communication channels. We also correct some errors from the literature, offer new proofs of some historical results, and give bounds for channel capacity. Special function techniques are employed to express the results in closed form. We are interested in a specific type of covert channel, a timing channel. A timing channel exists if it is possible for High to interfere with the system response time to an input by Low. Therefore, a timing channel is a communication channel where the output alphabet is constructed from different time values. However, the thrust of the paper is the analysis of timing channels that are discrete, memoryless, and noiseless. We call such a timing channel a simple timing channel (STC).>

Polarimetric and interferometric SAR data are frequently multilook processed for speckle reduction and data compression. The statistical characteristics of multilook data are quite different from those of single-look data. The authors investigate the statistics of their intensity and phase. Probability density function (PDF's) of the multilook phase difference, magnitude of complex product, and intensity and amplitude ratios between two components of the scattering matrix are derived, and expressed in closed forms. The PDF's depend on the complex correlation coefficient and the number of looks. Comparisons of these theoretically derived PDF's are made to measurements from NASA/JPL AIRSAR data. The results of this paper can be applied to feature classification using polarimetric SAR and to the estimation of decorrelation effects of the interferometric SAR.>

An optimization problem in calculating the bandwidth of a covert timing channel is discussed. In particular, the question of how dependent the bandwidth is on the magnitude of the modulation is addressed. A generalization of that covert channel is presented and its bandwidth (capacity) is studied. Attention is given to how the delay that HIGH uses to signal LOW affects the bandwidth. Increasing the delay lessens the noise but increases the time required to pass a symbol along the channel. What the optimal delay should be and how it influences the security of the system was studied. Because of the complicated nature of the formulas involved, closed-form solutions for some of the terms of interest cannot be given. Instead, numerical techniques and plotted results are used.>

The effect of noise on a simple covert timing channel is investigated. Shannon's information theory is used to quantify the resulting information flow across the channel. In particular, how a probabilistic response time to a query by the receiver affects the mutual information and channel capacity is studied. The channel capacity is expressed in terms of the critical probability for the mutual information function which is given in closed form in terms of Wright's hypergeometric function.>