A Key-Recovery Attack on SOBER-128

In this talk we consider linear approximations of layered cipher constructions with secret key-dependent constants that are inserted between layers, and where the layers have strong interdependency. Then clearly, averaging over the constant would clearly be wrong as it will break the interdependencies, and the Piling Up-lemma cannot be used. We show how to use linear approximations to divide the constants into constant classes, not necessary determined by a linear relation. As an example, a nonlinear filter generator SOBER-128 is considered and we show how to extend Matsui\u27s Algorithm I in this case. Also the possibility of using multiple linear approximations simultaneously is considered

Learning disentangled speech representations

A variety of informational factors are contained within the speech signal and a single short recording of speech reveals much more than the spoken words. The best method to extract and represent informational factors from the speech signal ultimately depends on which informational factors are desired and how they will be used. In addition, sometimes methods will capture more than one informational factor at the same time such as speaker identity, spoken content, and speaker prosody. The goal of this dissertation is to explore different ways to deconstruct the speech signal into abstract representations that can be learned and later reused in various speech technology tasks. This task of deconstructing, also known as disentanglement, is a form of distributed representation learning. As a general approach to disentanglement, there are some guiding principles that elaborate what a learned representation should contain as well as how it should function. In particular, learned representations should contain all of the requisite information in a more compact manner, be interpretable, remove nuisance factors of irrelevant information, be useful in downstream tasks, and independent of the task at hand. The learned representations should also be able to answer counter-factual questions. In some cases, learned speech representations can be re-assembled in different ways according to the requirements of downstream applications. For example, in a voice conversion task, the speech content is retained while the speaker identity is changed. And in a content-privacy task, some targeted content may be concealed without affecting how surrounding words sound. While there is no single-best method to disentangle all types of factors, some end-to-end approaches demonstrate a promising degree of generalization to diverse speech tasks. This thesis explores a variety of use-cases for disentangled representations including phone recognition, speaker diarization, linguistic code-switching, voice conversion, and content-based privacy masking. Speech representations can also be utilised for automatically assessing the quality and authenticity of speech, such as automatic MOS ratings or detecting deep fakes. The meaning of the term "disentanglement" is not well defined in previous work, and it has acquired several meanings depending on the domain (e.g. image vs. speech). Sometimes the term "disentanglement" is used interchangeably with the term "factorization". This thesis proposes that disentanglement of speech is distinct, and offers a viewpoint of disentanglement that can be considered both theoretically and practically

Covert timing channels, caching, and cryptography

Side-channel analysis is a cryptanalytic technique that targets not the formal description of a cryptographic primitive but the implementation of it. Examples of side-channels include power consumption or timing measurements. This is a young but very active field within applied cryptography. Modern processors are equipped with numerous mechanisms to improve the average performance of a program, including but not limited to caches. These mechanisms can often be used as side-channels to attack software implementations of cryptosystems. This area within side-channel analysis is called microarchitecture attacks, and those dealing with caching mechanisms cache-timing attacks. This dissertation presents a number of contributions to the field of side-channel analysis. The introductory portion consists of a review of common cache architectures, a literature survey of covert channels focusing mostly on covert timing channels, and a literature survey of cache-timing attacks, including selective related results that are more generally categorized as side-channel attacks such as traditional timing attacks. This dissertation includes eight publications relating to this field. They contain contributions in areas such as side-channel analysis, data cache-timing attacks, instruction cache-timing attacks, traditional timing attacks, and fault attacks. Fundamental themes also include attack mitigations and efficient yet secure software implementation of cryptosystems. Concrete results include, but are not limited to, four practical side-channel attacks against OpenSSL, each implemented and leading to full key recovery

Studies on Some Biological Reactions of Agricultural Interest

The general introduction out lines briefly, with particular reference to ribonucleases, the character of the enzymes which depolymerise nucleic acids. The publication by H. S. Kaplan and L. A. Heppel in J. Biol. Chem. 222 907 (1956) that a heat stable ribonuclease M. W. 2,000 - 5,000 could be isolated from calf spleen led to the research work presented in this thesis. These workers reported the purification of a ribonuclease similar to pancreatic ribonuclease in heat stability and specificity. Publications by other workers revealed that several ribonuclease activities could be extracted from calf spleen. The work reported here describes the procedures taken to purify the low molecular weight ribonuclease. Since several ribonucleases were reported, the original purification scheme of Kaplan and Heppel was adhered to initially. Section I outlines this procedure and the salient points are highlighted. In addition to a heat treatment there were four fractionations by conventional precipitation techniques, a lengthy dialysis and an Amberlite resin treatment. Section II, in addition to drafting the criteria for enzyme isolation and purification, reports the investigation of the techniques used originally by these workers. The unfavourable results obtained are presented in detail. Although an equivalent purification was achieved the yield of heat stable ribonuclease activity was poor. Each of the steps rejected ~50% of the activity. With the exception of the heat treatment which was considered essential, this original system was abandoned in favour of preliminary fractionation end concentration by precipitation with ammonium sulphate before and after the heat treatment. In this way ~75% of the heat stable activity was concentrated ready for molecular sieve and ion exchange chromatography. Section III reports the chromatography procedures undertaken to develop a purification scheme for the heat stable spleen ribonuclease. Some early experiments on the gel filtration behaviour of the active sample, particularly with respect to pancreatic ribonueleaee, are described. Gel filtration on a Sephadex G-75 column, 5cm x 75cm, developed to desalt the crude spleen sample. This measure eliminated the lengthy dialysis and achieved a complete recovery of activity with some purification. The desalting technique was followed by ion exchange chromatography. Chromatography on a Carboxymethyl-cellulose column fractionated the heat stable sample into two ribonuclease active peaks "A" and "B". A satisfactory adsorption of the crude sample on the C. M. cellulose was difficult to effect initially thus the sample was reduced by passing it through Diethylaminoethyl-cellulose as a pretreatment. All the ribonuclease activity passed through the column leaving ~37% of the contaminants adsorbed. The preliminary column work necessary to achieve the fractionation on C. M. cellulose using a gradient elution system is described. This column method was scaled up tenfold to cope with the large quantity of crude spleen preparation and prepare sufficient amounts of the active peaks "A" and "B" for rachromatography. Rechromatography on Carboxymethyl Sephadex revealed an elution irregularity at the chromatography on C.M. cellulose. Although ribonuclease active peak "B" was eluted as a single peak, the active peak "A" on rechromatography split into two peaks, one of which was eluted at a similar position to active peak "B". This indicated a distribution of activity for peak "A" similar to the chromatography of the crude preparation. On subsequent chromatography the rechromatographed peak "A" did not split again. These results indicated that calf spleen contains two heat stable ribonucleases. The activity "A" amounted to 16% of the total heat stable ribonuclease as determined by the general assay method. This activity was shown to be as heat stable as the bulk of the reparation. Attempts are made to explain the irregular chromatography effect. Section IV outlines the merit of disc electrophoresis on polyacrylamide gels as a technique for estimating the purity of protein samples. The spleen ribenuclease fractions "A" and "B" were examined by this technique. It was demonstrated that active fraction "B" had been extensively purified and had an electrophoretic mobility similar to pancreatic ribonuclease. Active fraction "A" though considerably purified contained at least three contaminants. An estimate of the molecular weights of the two ribonucleases is presented in Section V. A linear relationship exists between elution volume and log. (molecular weight) for globular proteins at gel filtration. To carry out the estimation, a Sephadex G-75 column was calibrated by protein standards of known molecular weight and gel filtration behaviour. After determining the elution volumes for the heat stable spleen ribonucleases, molecular weights of ~24,000 and 10,000 were attributed to activity "A" and activity "B" respectively. Ho evidence could be found to support the previous report that a heat stable ribonuclease M.W. 2,000-5,000 was present in calf spleen