A Comparison of Perfect Table Cryptanalytic Tradeoff Algorithms

The performances of three major time memory tradeoff algorithms were compared in a recent paper. The algorithms considered there were the classical Hellman tradeoff and the non-perfect table versions of the distinguished point method and the rainbow table method. This paper adds the perfect table versions of the distinguished point method and the rainbow table method to the list, so that all the major tradeoff algorithms may now be compared against each other. Even though there are existing claims as to the superiority of one tradeoff algorithm over another algorithm, the algorithm performance comparisons provided by the current work and the recent preceding paper are of more practical value. Comparisons that take both the cost of pre-computation and the efficiency of the online phase into account, at parameters that achieve a common success rate, can now be carried out with ease. Comparisons can be based on the expected execution complexities rather than the worst case complexities, and details such as the effects of false alarms and various storage optimization techniques need no longer be ignored. A significant portion of this paper is allocated to accurately analyzing the execution behavior of the perfect table distinguished point method. In particular, we obtain a closed-form formula for the average length of chains associated with a perfect distinguished point table

LIPIcs, Volume 248, ISAAC 2022, Complete Volume

LIPIcs, Volume 248, ISAAC 2022, Complete Volum

Generalization Through the Lens of Learning Dynamics

A machine learning (ML) system must learn not only to match the output of a target function on a training set, but also to generalize to novel situations in order to yield accurate predictions at deployment. In most practical applications, the user cannot exhaustively enumerate every possible input to the model; strong generalization performance is therefore crucial to the development of ML systems which are performant and reliable enough to be deployed in the real world. While generalization is well-understood theoretically in a number of hypothesis classes, the impressive generalization performance of deep neural networks has stymied theoreticians. In deep reinforcement learning (RL), our understanding of generalization is further complicated by the conflict between generalization and stability in widely-used RL algorithms. This thesis will provide insight into generalization by studying the learning dynamics of deep neural networks in both supervised and reinforcement learning tasks.Comment: PhD Thesi

Methodology for malleable applications on distributed memory systems

A la portada logo BSC(English) The dominant programming approach for scientific and industrial computing on clusters is MPI+X. While there are a variety of approaches within the node, denoted by the ``X'', Message Passing interface (MPI) is the standard for programming multiple nodes with distributed memory. This thesis argues that the OmpSs-2 tasking model can be extended beyond the node to naturally support distributed memory, with three benefits: First, at small to medium scale the tasking model is a simpler and more productive alternative to MPI. It eliminates the need to distribute the data explicitly and convert all dependencies into explicit message passing. It also avoids the complexity of hybrid programming using MPI+X. Second, the ability to offload parts of the computation among the nodes enables the runtime to automatically balance the loads in a full-scale MPI+X program. This approach does not require a cost model, and it is able to transparently balance the computational loads across the whole program, on all its nodes. Third, because the runtime handles all low-level aspects of data distribution and communication, it can change the resource allocation dynamically, in a way that is transparent to the application. This thesis describes the design, development and evaluation of OmpSs-2@Cluster, a programming model and runtime system that extends the OmpSs-2 model to allow a virtually unmodified OmpSs-2 program to run across multiple distributed memory nodes. For well-balanced applications it provides similar performance to MPI+OpenMP on up to 16 nodes, and it improves performance by up to 2x for irregular and unbalanced applications like Cholesky factorization. This work also extended OmpSs-2@Cluster for interoperability with MPI and Barcelona Supercomputing Center (BSC)'s state-of-the-art Dynamic Load Balance (DLB) library in order to dynamically balance MPI+OmpSs-2 applications by transparently offloading tasks among nodes. This approach reduces the execution time of a microscale solid mechanics application by 46% on 64 nodes and on a synthetic benchmark, it is within 10% of perfect load balancing on up to 8 nodes. Finally, the runtime was extended to transparently support malleability for pure OmpSs-2@Cluster programs and interoperate with the Resources Management System (RMS). The only change to the application is to explicitly call an API function to control the addition or removal of nodes. In this regard we additionally provide the runtime with the ability to semi-transparently save and recover part of the application status to perform checkpoint and restart. Such a feature hides the complexity of data redistribution and parallel IO from the user while allowing the program to recover and continue previous executions. Our work is a starting point for future research on fault tolerance. In summary, OmpSs-2@Cluster expands the OmpSs-2 programming model to encompass distributed memory clusters. It allows an existing OmpSs-2 program, with few if any changes, to run across multiple nodes. OmpSs-2@Cluster supports transparent multi-node dynamic load balancing for MPI+OmpSs-2 programs, and enables semi-transparent malleability for OmpSs-2@Cluster programs. The runtime system has a high level of stability and performance, and it opens several avenues for future work.(Español) El modelo de programación dominante para clusters tanto en ciencia como industria es actualmente MPI+X. A pesar de que hay alguna variedad de alternativas para programar dentro de un nodo (indicado por la "X"), el estandar para programar múltiples nodos con memoria distribuida sigue siendo Message Passing Interface (MPI). Esta tesis propone la extensión del modelo de programación basado en tareas OmpSs-2 para su funcionamiento en sistemas de memoria distribuida, destacando 3 beneficios principales: En primer lugar; a pequeña y mediana escala, un modelo basado en tareas es más simple y productivo que MPI y elimina la necesidad de distribuir los datos explícitamente y convertir todas las dependencias en mensajes. Además, evita la complejidad de la programacion híbrida MPI+X. En segundo lugar; la capacidad de enviar partes del cálculo entre los nodos permite a la librería balancear la carga de trabajo en programas MPI+X a gran escala. Este enfoque no necesita un modelo de coste y permite equilibrar cargas transversalmente en todo el programa y todos los nodos. En tercer lugar; teniendo en cuenta que es la librería quien maneja todos los aspectos relacionados con distribución y transferencia de datos, es posible la modificación dinámica y transparente de los recursos que utiliza la aplicación. Esta tesis describe el diseño, desarrollo y evaluación de OmpSs-2@Cluster; un modelo de programación y librería que extiende OmpSs-2 permitiendo la ejecución de programas OmpSs-2 existentes en múltiples nodos sin prácticamente necesidad de modificarlos. Para aplicaciones balanceadas, este modelo proporciona un rendimiento similar a MPI+OpenMP hasta 16 nodos y duplica el rendimiento en aplicaciones irregulares o desbalanceadas como la factorización de Cholesky. Este trabajo incluye la extensión de OmpSs-2@Cluster para interactuar con MPI y la librería de balanceo de carga Dynamic Load Balancing (DLB) desarrollada en el Barcelona Supercomputing Center (BSC). De este modo es posible equilibrar aplicaciones MPI+OmpSs-2 mediante la transferencia transparente de tareas entre nodos. Este enfoque reduce el tiempo de ejecución de una aplicación de mecánica de sólidos a micro-escala en un 46% en 64 nodos; en algunos experimentos hasta 8 nodos se pudo equilibrar perfectamente la carga con una diferencia inferior al 10% del equilibrio perfecto. Finalmente, se implementó otra extensión de la librería para realizar operaciones de maleabilidad en programas OmpSs-2@Cluster e interactuar con el Sistema de Manejo de Recursos (RMS). El único cambio requerido en la aplicación es la llamada explicita a una función de la interfaz que controla la adición o eliminación de nodos. Además, se agregó la funcionalidad de guardar y recuperar parte del estado de la aplicación de forma semitransparente con el objetivo de realizar operaciones de salva-reinicio. Dicha funcionalidad oculta al usuario la complejidad de la redistribución de datos y las operaciones de lectura-escritura en paralelo, mientras permite al programa recuperar y continuar ejecuciones previas. Este es un punto de partida para futuras investigaciones en tolerancia a fallos. En resumen, OmpSs-2@Cluster amplía el modelo de programación de OmpSs-2 para abarcar sistemas de memoria distribuida. El modelo permite la ejecución de programas OmpSs-2 en múltiples nodos prácticamente sin necesidad de modificarlos. OmpSs-2@Cluster permite además el balanceo dinámico de carga en aplicaciones híbridas MPI+OmpSs-2 ejecutadas en varios nodos y es capaz de realizar maleabilidad semi-transparente en programas OmpSs-2@Cluster puros. La librería tiene un niveles de rendimiento y estabilidad altos y abre varios caminos para trabajos futuro.Arquitectura de computador

John Savage

U radu je realiziran laboratorijski model sustava upravljanja sinkronim strojem sa stalnim magnetima. Prilikom realizacije laboratorijskog modela koristiti se industrijski pretvarač frekvencije i napona Siemens Sinamics S120, programibilni logički kontroler (PLC) Siemens Simatic serije S7-300 i sinkroni stroj sa stalnim magnetima. PLC i pretvarač frekvencije i napona su povezani preko industrijske komunikacijske mreže PROFINET. Programskim paketom Starter konfiguriran je pretvarač i sinkroni motor sa stalnim magnetima, a pomoću TIA Portala izvršava se upravljanje cjelokupnim sustavom.For the realization of the laboratory model we used the Siemens Sinamics S120 industrial frequency and voltage inverter, Siemens Simatic S7-300 programmable logic controller (PLC) and a synchronous machine with permanent magnets. The PLC and the frequency and voltage inverter are connected via the PROFINET industrial communication network. Programming package Starter is used for configuration of inverter and synchronous machine drive with permanent magnets and TIA Portal is used for overall system management

Obiter Dicta

"Stitched together over five years of journaling, Obiter Dicta is a commonplace book of freewheeling explorations representing the transcription of a dozen notebooks, since painstakingly reimagined for publication. Organized after Theodor Adorno’s Minima Moralia, this unschooled exercise in aesthetic thought—gleefully dilettantish, oftentimes dangerously close to the epigrammatic—interrogates an array of subject matter (although inescapably circling back to the curiously resemblant histories of Western visual art and instrumental music) through the lens of drive-by speculation. Erick Verran’s approach to philosophical inquiry follows the brute-force literary technique of Jacques Derrida to exhaustively favor the material grammar of a signifier over hand-me-down meaning, juxtaposing outer semblances with their buried systems and our etched-in-stone intuitions about color and illusion, shape and value, with lessons stolen from seemingly unrelatable disciplines. Interlarded with extracts of Ludwig Wittgenstein but also Wallace Stevens, Cormac McCarthy as well as Roland Barthes, this cache of incidental remarks eschews what’s granular for the biggest picture available, leaving below the hyper-specialized fields of academia for a bird’s-eye view of their crop circles. Obiter Dicta is an unapologetic experiment in intellectual dot-connecting that challenges much long-standing wisdom about everything from illuminated manuscripts to Minecraft and the evolution of European music with lyrical brevity; that is, before jumping to the next topic.

The Challenge Of Strategic Flexibility: A Case Study

Abstract Strategic Flexibility has been widely cited as a critical success factor and capability for navigating today’s complex and dynamic business landscape. Despite this recognition, there remain considerable challenges in the conceptual understanding and implementation of this strategic principle. Strategic flexibility has also been linked to strategic decision making as the extent to which new and alternative options in strategic decision making are generated and considered. This relationship plays a key role in effective firm response and when combined with a strategically designed leadership pipeline it can result in a valuable source of competitive advantage. Yet we know very little about the interplay between particular environments and the factors that influence executives’ strategic frames as little empirical research has been conducted in this area. Therefore, this study extends knowledge of these relationships by investigating the strategic frames of senior executives, the contexts and the factors that influence their capability for cognitive strategic flexibility. The study explores strategic thinking and decision-making at the individual and organizational levels. Thus, it falls under the Individual and Organizational Minds research stream with significant influence by the two cognitive branches of Information Processing Perspective and Ideological Perspectives. A qualitative and inductive case study method was employed with the use of the Kelley Repertory Grid Interview technique. Consistent with the interpretivist philosophy, this qualitative research focuses on the perceptions and experiences of the participants in the work context. The study revealed multiple factors inhibiting the cognitive strategic flexibility of the individual executives. It also develops new conceptual connections between the Strategic Flexibility and Ambidexterity research streams that show promise for enabling strategic thinking in practice. The inductive creation of the new iSCOPE Framework from this research provides a useful tool that integrates academic theories and facilitates the development of intervention solutions that are concrete, mutually reinforcing and systematic