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This thesis investigates the prevention of error propagation in magnetically recorded compressed data when severe environmental conditions result in uncorrected channel errors. The tape format DDS is examined and a computer simulation of its error correction procedures is described. This software implementation uses explicit parity byte equations and these are presented for all three Reed-Solomon codes. The simulation allows the calculation of the uncorrected error patterns when the recording is compromised and uncorrected byte errors are determined for given initial random and burst errors. Some of the more familiar data compression algorithms are visited before the little known adaptive Rice algorithm is described in detail. An analytic example is developed which demonstrates the coding mechanism. A synchronized piecewise compression strategy is adopted in which the synchronizing sequences are placed periodically into the compressed data stream. The synchronizing sequences are independent of the compression algorithm and may occur naturally in the compressed data stream. A cyclic count is added to the compressed data stream to number the groups of data between synchronizing sequences and prevent slippage in the data. The Rice algorithm is employed in the strategy to compress correlated physical data. A novel compressor is developed to compress mixed correlated physical data and text within the synchronization strategy. This compressor uses the Rice algorithm to compress the correlated data and a sliding window algorithm to compress the text and switches between the two algorithms as the data type varies. The sliding window compressor T.ZR is adopted when the same principles are applied to the robust compression of English text alone. TJ7R is modified to improve compression of relatively small pieces of English text. The synchronization strategy incorporating these algorithms has been simulated computationally. This simulation is linked to that of DDS in each test performed when the errors are both random and bursty. The decompressed data is compared to the original. The strategy is demonstrated to be effective in preventing error propagation beyond the data immediately affected by errors without significant damage to the compression ratio.

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Lambda encodings (such as Church encoding, Scott encoding and Parigot encoding) are methods to represent data in lambda calculus. Curry-Howard correspondence relates the formulas and proofs in intuitionistic logics to the types and programs in typed functional programming languages. Roughly speaking, Type theory (Intuitionistic Type Theory) formulates the intuitionistic logic in the style of typed functional programming language. This dissertation investigates the mechanisms to support lambda encodings in type theory. Type theory, for example, Calculus of Constructions(CC) does not directly support inductive data because the induction principle for the inductive data is proven to be not derivable. Thus inductive data together with inductive principle are added as primitive to CC, leading to several nontrivial extensions, e.g. Calculus of Inductive Constructions. In this dissertation, we explore alternatives to incorporate inductive data in type theory. We propose to consider adding an abstraction construct to the intuitionistic type to support lambda-encoded data, while still be able to derive the corresponding induction principle. The main benefit of this approach is that we obtain relatively simple systems, which are easier to analyze and implement.

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We show that information leakage occurs in video over IP traffic, including for encrypted payloads. It is possible to detect events occurring in the field of view of a camera streaming live video through analysis of network traffic metadata including arrival time between packets, packets sizes, and video stream bandwidth. Event detection through metadata analysis is possible even when common encryption techniques are applied to the video stream such as SSL or AES. We have observed information leakage across multiple codes and cameras. Through timestamps added to the x264 codec, we establish a basis for detectability of events via packet timing. Laboratory experiments confirm that this event detection is possible in practice and repeatable. By collecting network traffic captures from over 100 Skype video calls we are able to see the impact of this information leakage under a variety of conditions.

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