Development of rate-compatible structured LDPC CODEC algorithms and hardware IP

Issued as final reportSamsung Advanced Institute of Technolog

On Compression of Data Encrypted with Block Ciphers

This paper investigates compression of data encrypted with block ciphers, such as the Advanced Encryption Standard (AES). It is shown that such data can be feasibly compressed without knowledge of the secret key. Block ciphers operating in various chaining modes are considered and it is shown how compression can be achieved without compromising security of the encryption scheme. Further, it is shown that there exists a fundamental limitation to the practical compressibility of block ciphers when no chaining is used between blocks. Some performance results for practical code constructions used to compress binary sources are presented

On applications of puncturing in error-correction coding

This thesis investigates applications of puncturing in error-correction coding and physical layer security with an emphasis on binary and non-binary LDPC codes. Theoretical framework for the analysis of punctured binary LDPC codes at short block lengths is developed and a novel decoding scheme is designed that achieves considerably faster convergence than conventional approaches. Subsequently, optimized puncturing and shortening is studied for non-binary LDPC codes over binary input channels. Framework for the analysis of punctured/shortened non-binary LDPC codes over the BEC channel is developed, which enables the optimization of puncturing and shortening patterns. Insight from this analysis is used to develop algorithms for puncturing and shortening of non-binary LDPC codes at finite block lengths that perform well. It is confirmed that symbol-wise puncturing is generally bad and that bit-wise punctured non-binary LDPC codes can significantly outperform their binary counterparts, thus making them an attractive solution for future communication systems; both for error-correction and distributed compression. Puncturing is also considered in the context of physical layer security. It is shown that puncturing can be used effectively for coding over the wiretap channel to hide the message bits from eavesdroppers. Further, it is shown how puncturing patterns can be optimized for enhanced secrecy. Asymptotic analysis confirms that eavesdroppers are forced to operate at BERs very close to 0.5, even if their signal is only slightly worse than that of the legitimate receivers. The proposed coding scheme is naturally applicable at finite block lengths and allows for efficient, almost-linear time encoding. Finally, it is shown how error-correcting codes can be used to solve an open problem of compressing data encrypted with block ciphers such as AES. Coding schemes for multiple chaining modes are proposed and it is verified that considerable compression gains are attainable for binary sources.Ph.D.Committee Chair: McLaughlin, Steven; Committee Member: Barry, John; Committee Member: Blough, Douglas; Committee Member: Fekri, Faramarz; Committee Member: Lee, Wenk