Digital rights management (DRM) - watermark encoding scheme for JPEG images

The aim of this dissertation is to develop a new algorithm to embed a watermark in JPEG compressed images, using encoding methods. This encompasses the embedding of proprietary information, such as identity and authentication bitstrings, into the compressed material. This watermark encoding scheme involves combining entropy coding with homophonic coding, in order to embed a watermark in a JPEG image. Arithmetic coding was used as the entropy encoder for this scheme. It is often desired to obtain a robust digital watermarking method that does not distort the digital image, even if this implies that the image is slightly expanded in size before final compression. In this dissertation an algorithm that combines homophonic and arithmetic coding for JPEG images was developed and implemented in software. A detailed analysis of this algorithm is given and the compression (in number of bits) obtained when using the newly developed algorithm (homophonic and arithmetic coding). This research shows that homophonic coding can be used to embed a watermark in a JPEG image by using the watermark information for the selection of the homophones. The proposed algorithm can thus be viewed as a ‘key-less’ encryption technique, where an external bitstring is used as a ‘key’ and is embedded intrinsically into the message stream. The algorithm has achieved to create JPEG images with minimal distortion, with Peak Signal to Noise Ratios (PSNR) of above 35dB. The resulting increase in the entropy of the file is within the expected 2 bits per symbol. This research endeavor consequently provides a unique watermarking technique for images compressed using the JPEG standard.Dissertation (MEng)--University of Pretoria, 2008.Electrical, Electronic and Computer Engineeringunrestricte

Universal homophonic coding

Redundancy in plaintext is a fertile source of attack in any encryption system. Compression before encryption reduces the redundancy in the plaintext, but this does not make a cipher more secure. The cipher text is still susceptible to known-plaintext and chosen-plaintext attacks. The aim of homophonic coding is to convert a plaintext source into a random sequence by randomly mapping each source symbol into one of a set of homophones. Each homophone is then encoded by a source coder after which it can be encrypted with a cryptographic system. The security of homophonic coding falls into the class of unconditionally secure ciphers. The main advantage of homophonic coding over pure source coding is that it provides security both against known-plaintext and chosen-plaintext attacks, whereas source coding merely protects against a ciphertext-only attack. The aim of this dissertation is to investigate the implementation of an adaptive homophonic coder based on an arithmetic coder. This type of homophonic coding is termed universal, as it is not dependent on the source statistics.Computer ScienceM.Sc. (Computer Science

Adaptive homophonic coding techniques for enhanced e-commerce security

This dissertation considers a method to convert an ordinary cipher system, as used to secure e-commerce transactions, into an unconditionally secure cipher system, i.e. one that generates ciphertext that does not contain enough statistical information to break the cipher, irrespective of how much ciphertext is available. Shannon showed that this can be achieved by maximizing the entropy of the message sequence to be encrypted. This, in turn, achieved by means of homophonic coding. Homophonic coding substitutes characters in the message source with randomly chosen codewords. It offers the advantage that it enables protection against known- and chosen plaintext attacks on cipher algorithms since source statistics are randomly changed before encryption. The disadvantage of homophonic substitution is that it will in general increase the length of the message sequence. To compensate for this, homophonic coding is combined with the data compression algorithm known as arithmetic coding. It is shown that the arithmetic coding algorithm can be adapted to perform homophonic coding by dyadically decomposing the character probabilities in its probability estimation phase. By doing this, a faster version of arithmetic coding, known as shift-and-add arithmetic coding can be implemented. A new method of statistical modelling, based on an Infinite Impulse Response filtering method is presented. A method to adapt the well-known Lempel-Ziv- Welch compression algorithm to perform homophonic coding is also presented. The procedure involves a bit-wise exclusive-or randomization operation during encoding. The results show that the adapted algorithms do indeed increase the entropy of the source sequences by no more than 2 bits/symbol, and even offers compression in some cases.Dissertation (MEng (Data Security))--University of Pretoria, 2006.Electrical, Electronic and Computer Engineeringunrestricte

Cryptanalysis of the Purple Cipher using Random Restarts

Cryptanalysis is the process of trying to analyze ciphers, cipher text, and crypto systems, which may exploit any loopholes or weaknesses in the systems, leading us to an understanding of the key used to encrypt the data. This project uses Expectation Maximization (EM) approach using numerous restarts to attack decipherment problems such as the Purple Cipher. In this research, we perform cryptanalysis of the Purple cipher using genetic algorithms and hidden Markov models (HMM). If the Purple cipher has a fixed plugboard, we show that genetic algorithms are successful in retrieving the plaintext from cipher text with high accuracy. On the other hand, if the cipher has a plugboard that is not fixed, we can decrypt the cipher text with increasing accuracy given an increase in population size and restarts. We performed the cryptanalysis of PseudoPurple, which is less complex but more powerful than Purple using HMMs. Though we could not decrypt cipher text produced by PseudoPurple with good accuracy, there is an increase in accuracy of the decrypted plaintext with an increase in the number of restarts

Security of Ubiquitous Computing Systems

The chapters in this open access book arise out of the EU Cost Action project Cryptacus, the objective of which was to improve and adapt existent cryptanalysis methodologies and tools to the ubiquitous computing framework. The cryptanalysis implemented lies along four axes: cryptographic models, cryptanalysis of building blocks, hardware and software security engineering, and security assessment of real-world systems. The authors are top-class researchers in security and cryptography, and the contributions are of value to researchers and practitioners in these domains. This book is open access under a CC BY license

Evaluating SMS parsing using automated testing software

Mobile phones are ubiquitous with millions of users acquiring them every day for personal, business and social usage or communication. Its enormous pervasiveness has created a great advantage for its use as a technological tool applicable to overcome the challenges of information dissemination regarding burning issues, advertisement, and health related matters. Short message services (SMS), an integral functional part of cell phones, can be turned into a major tool for accessing databases of information on HIV/AIDS as appreciable percentage of the youth embrace the technology. The common features by the users of the unique language are the un-grammatical structure, convenience of spelling, homophony of words and alphanumeric mix up of the arrangement of words. This proves it to be difficult to serve as query in the search engine architecture. In this work SMS query was used for information accessing in Frequently Asked Question FAQ system under a specified medical domain. Finally, when the developed system was measured in terms of proximity to the answer retrieved remarkable results were observed

Ensembles working towards performance: Emerging coordination and interactions in self-organised groups

For small ensembles, preparing for ensemble performance is often achieved through a framework of rehearsals and performance goals. The ways that groups work together varies widely, but generally involves the concurrent evolution of social and task behaviours. Time as factor within and across a series of ensemble rehearsals has not been extensively studied. Research on organisations increasingly recognises the value of studying groups as dynamic, emergent entities. As well as the specific musical tasks and processes involved, this research takes a broader perspective, incorporating investigations of moment-by-moment verbal interactions between group members, and the way the explicit and implicit communication processes evolve over time. This research aimed to address the central question of how behavioural interactions in small ensembles emerge and change over time. It aimed to investigate the ways that ensembles work together in rehearsal, in particular as a way of preparing for performance. The key theoretical perspectives on which this research is based are concerned with processes of coordination in small groups, in which the ensemble is viewed as a dynamic, self-managed collective. This was a mixed methods study including a questionnaire study, quantitative measures of verbal interactions, and qualitative analysis of participant experiences and perceptions. A background survey on rehearsal methods was conducted with small ensembles (< 12 members), along with two longitudinal case studies of newly formed a cappella vocal quintets. Rehearsals were video-recorded in the field (Case 1) and in a laboratory setting (Case 2) over a three-month period. Verbal interactions were captured, and the rehearsal utterances were time-stamped and coded. Behaviours were analysed using the software Theme (Patternvision Ltd) to identify recurrent temporal interaction patterns (‘T-patterns). In Case 2, further aspects were incorporated – two contrasting pieces were provided for rehearsals, and musical and verbal interactions were explored. Finally, a qualitative study combined interview, observation and visual methods explored experiences from participants of both case studies. The emergence of interactions, implicit communication and rehearsal activities were subject to a series of transitional changes triggered by exogenous factors, including approaching deadlines and social familiarity. Survey findings showed differences in rehearsal structure at different stages of preparation, but also commonalities across a range of types and sizes of ensembles. In the case studies, patterns in behaviour were evident at two main levels of analysis – emergent, inter-individual interactions ‘in the moment’, and in progressions through phases over a series of rehearsals. Verbal interaction patterns contributed were evident from first encounters onwards; patterns appeared very early and increased in complexity over time, as implicit communication modes became more established. Three phases were identified – an initial exploration phase where social and task familiarity were established, a transition phase where differences were surfaced and resolved, and a final integration phase in which a shared plan for performance was realised. The findings also showed that over time, implicit coordination increased and explicit coordination modes decreased. A new model of ensemble processes was proposed, in which the emergent interactions and larger-scale transitional phases are combined. This research provided a new perspective on collaboration in music ensembles. It offered implications for further research on small group processes and their emergence over time, and for music ensemble performers and teachers seeking to reflect on practice. In describing these processes and their predictable ‘transition’ points, the metaphor of a river was used as a powerful image of change and renewal. It recognised ways that small groups, including music ensembles, need to balance paradoxical forces for predictability and structure with creativity and sharing of ideas. It also contributed to methods, both in its longitudinal design and the combination of approaches to investigation. Finally, the thesis highlighted further possibilities for interdisciplinary research in self-organised music ensembles and small group research

Security of Ubiquitous Computing Systems

The chapters in this open access book arise out of the EU Cost Action project Cryptacus, the objective of which was to improve and adapt existent cryptanalysis methodologies and tools to the ubiquitous computing framework. The cryptanalysis implemented lies along four axes: cryptographic models, cryptanalysis of building blocks, hardware and software security engineering, and security assessment of real-world systems. The authors are top-class researchers in security and cryptography, and the contributions are of value to researchers and practitioners in these domains. This book is open access under a CC BY license