Fast Digital Convolutions using Bit-Shifts

An exact, one-to-one transform is presented that not only allows digital circular convolutions, but is free from multiplications and quantisation errors for transform lengths of arbitrary powers of two. The transform is analogous to the Discrete Fourier Transform, with the canonical harmonics replaced by a set of cyclic integers computed using only bit-shifts and additions modulo a prime number. The prime number may be selected to occupy contemporary word sizes or to be very large for cryptographic or data hiding applications. The transform is an extension of the Rader Transforms via Carmichael's Theorem. These properties allow for exact convolutions that are impervious to numerical overflow and to utilise Fast Fourier Transform algorithms.Comment: 4 pages, 2 figures, submitted to IEEE Signal Processing Letter

AdSplit: Separating smartphone advertising from applications

A wide variety of smartphone applications today rely on third-party advertising services, which provide libraries that are linked into the hosting application. This situation is undesirable for both the application author and the advertiser. Advertising libraries require additional permissions, resulting in additional permission requests to users. Likewise, a malicious application could simulate the behavior of the advertising library, forging the user's interaction and effectively stealing money from the advertiser. This paper describes AdSplit, where we extended Android to allow an application and its advertising to run as separate processes, under separate user-ids, eliminating the need for applications to request permissions on behalf of their advertising libraries. We also leverage mechanisms from Quire to allow the remote server to validate the authenticity of client-side behavior. In this paper, we quantify the degree of permission bloat caused by advertising, with a study of thousands of downloaded apps. AdSplit automatically recompiles apps to extract their ad services, and we measure minimal runtime overhead. We also observe that most ad libraries just embed an HTML widget within and describe how AdSplit can be designed with this in mind to avoid any need for ads to have native code

Fast Mojette Transform for Discrete Tomography

A new algorithm for reconstructing a two dimensional object from a set of one dimensional projected views is presented that is both computationally exact and experimentally practical. The algorithm has a computational complexity of O(n log2 n) with n = N^2 for an NxN image, is robust in the presence of noise and produces no artefacts in the reconstruction process, as is the case with conventional tomographic methods. The reconstruction process is approximation free because the object is assumed to be discrete and utilizes fully discrete Radon transforms. Noise in the projection data can be suppressed further by introducing redundancy in the reconstruction. The number of projections required for exact reconstruction and the response to noise can be controlled without comprising the digital nature of the algorithm. The digital projections are those of the Mojette Transform, a form of discrete linogram. A simple analytical mapping is developed that compacts these projections exactly into symmetric periodic slices within the Discrete Fourier Transform. A new digital angle set is constructed that allows the periodic slices to completely fill all of the objects Discrete Fourier space. Techniques are proposed to acquire these digital projections experimentally to enable fast and robust two dimensional reconstructions.Comment: 22 pages, 13 figures, Submitted to Elsevier Signal Processin

Quire: Lightweight Provenance for Smart Phone Operating Systems

Smartphone apps often run with full privileges to access the network and sensitive local resources, making it difficult for remote systems to have any trust in the provenance of network connections they receive. Even within the phone, different apps with different privileges can communicate with one another, allowing one app to trick another into improperly exercising its privileges (a Confused Deputy attack). In Quire, we engineered two new security mechanisms into Android to address these issues. First, we track the call chain of IPCs, allowing an app the choice of operating with the diminished privileges of its callers or to act explicitly on its own behalf. Second, a lightweight signature scheme allows any app to create a signed statement that can be verified anywhere inside the phone. Both of these mechanisms are reflected in network RPCs, allowing remote systems visibility into the state of the phone when an RPC is made. We demonstrate the usefulness of Quire with two example applications. We built an advertising service, running distinctly from the app which wants to display ads, which can validate clicks passed to it from its host. We also built a payment service, allowing an app to issue a request which the payment service validates with the user. An app cannot not forge a payment request by directly connecting to the remote server, nor can the local payment service tamper with the request

Economic Analysis of Impact Assessment of Production Technology of Paddy Cultivation in Nasik Region of Maharashtra in India

The study had assessed the impact assessment of production technology of paddy cultivation in Nasik region of Maharashtra for the year 2016-17, based on the data of costs and returns. Analytical techniques like benefit-cost ratio (BCR), technology adoption index, yield gap, were exercised to have the extent of economic impact of improved paddy technology. High adopter group earned the net profit of ` 2298.09/ha (BCR=1.32) compared to ` 3629.3/ha ( BCR= 1.06) for low adopter group. Average technology adoption index was 71.57 per cent indicating that the farmers adopting recommended production technology of paddy could get yield of 41.63q/ha. Factor share analysis showed that contribution of Char-sutri method to the total yield was the highest yield (i.e. 32.84 per cent) which was followed by urea (19.76 per cent), doses of manures (12.02 per cent), intercultural operation, planting distance, transplanting time contributes about 8.09 per cent etc. respectively. Estimates of yield gap analysis proved existence of yield gap in all level which ranged from 41 percent (low adopter) to 23 percent (high adopter). So, reduction or bridging up the yield gap may be utmost priority to increase the overall production and income of the farmers

People with Learning Disabilities and Smartphones: Testing the Usability of a Touch-Screen Interface

Mobile phone technology is becoming ubiquitous. However, a number of unique usability challenges are still unresolved, including small screen size, device orientation changes, and an array of interaction methods (tap, flick, pinch, etc.) These challenges may be particularly acute for people with learning disabilities. This study examined the usability of touchscreen interactions, the difficulties, and possible solutions. An app was developed in which (12) participants accessed Google Maps and manipulated it to find various London Underground station locations. Text input (a password), tap, swipe, and pinch were required, and their usage was analysed. Many participants were successful in finding the required information. However, many difficulties arose, including misunderstandings of the labelling (a live ‘Welcome’ button was not tapped, whereas a short list of instructions was erroneously seen as a menu and so erroneously tapped to access each step in the process) and an over-sensitive zoom feature. Three categories of error were formulated from the findings: affordance, user, and functionality. Recommendations are offered, such as using more appropriate ‘signage’ for link buttons (affordance); manipulating the zoom feature using + and - buttons rather than a ‘pinch’, which requires two fingered dexterity (functionality); and more formal training and familiarity (user)

Algorithms for Replica Placement in High-Availability Storage

A new model of causal failure is presented and used to solve a novel replica placement problem in data centers. The model describes dependencies among system components as a directed graph. A replica placement is defined as a subset of vertices in such a graph. A criterion for optimizing replica placements is formalized and explained. In this work, the optimization goal is to avoid choosing placements in which a single failure event is likely to wipe out multiple replicas. Using this criterion, a fast algorithm is given for the scenario in which the dependency model is a tree. The main contribution of the paper is an $O(n + \rho \log \rho)$ dynamic programming algorithm for placing $\rho$ replicas on a tree with $n$ vertices. This algorithm exhibits the interesting property that only two subproblems need to be recursively considered at each stage. An $O(n^2 \rho)$ greedy algorithm is also briefly reported.Comment: 22 pages, 7 figures, 4 algorithm listing