Helsinki Institute for Information Technology

About: Helsinki Institute for Information Technology is a facility organization based out in Espoo, Finland. It is known for research contribution in the topics: Population & Bayesian network. The organization has 630 authors who have published 1962 publications receiving 63426 citations.

Discovering unconfounded causal relationships using linear non-gaussian models

Abstract: Causal relationships among a set of observed variables are often modeled using directed acyclic graph (DAG) structures, and learning such structures from data is known as the causal discovery problem. We here consider the learning of linear non-Gaussian acyclic models [9] with hidden variables [5]. Estimation of such models is computationally challenging and hence only possible when the number of variables is small. We present an algorithm for obtaining partial but in the large sample limit correct information about pairwise total causal effects in such a model. In particular, we obtain consistent estimates of the total effects for all variable pairs for which there exist an unconfounded superset of observed variables. Simulations show that the estimated pairwise total effects are good approximations of the true total effects.

PAC it up: Towards Pointer Integrity using ARM Pointer Authentication

Abstract: Run-time attacks against programs written in memory-unsafe programming languages (e.g., C and C++) remain a prominent threat against computer systems. The prevalence of techniques like return-oriented programming (ROP) in attacking real-world systems has prompted major processor manufacturers to design hardware-based countermeasures against specific classes of run-time attacks. An example is the recently added support for pointer authentication (PA) in the ARMv8-A processor architecture, commonly used in devices like smartphones. PA is a low-cost technique to authenticate pointers so as to resist memory vulnerabilities. It has been shown to enable practical protection against memory vulnerabilities that corrupt return addresses or function pointers. However, so far, PA has received very little attention as a general purpose protection mechanism to harden software against various classes of memory attacks. In this paper, we use PA to build novel defenses against various classes of run-time attacks, including the first PA-based mechanism for data pointer integrity. We present PARTS, an instrumentation framework that integrates our PA-based defenses into the LLVM compiler and the GNU/Linux operating system and show, via systematic evaluation, that PARTS provides better protection than current solutions at a reasonable performance overhead

Interaction with magic lenses: real-world validation of a Fitts' Law model

Abstract: Rohs and Oulasvirta (2008) proposed a two-component Fitts' law model for target acquisition with magic lenses in mobile augmented reality (AR) with 1) a physical pointing phase, in which the target can be directly observed on the background surface, and 2) a virtual pointing phase, in which the target can only be observed through the device display. The model provides a good fit (R2=0.88) with laboratory data, but it is not known if it generalizes to real-world AR tasks. In the present outdoor study, subjects (N=12) did building-selection tasks in an urban area. The differences in task characteristics to the laboratory study are drastic: targets are three-dimensional and they vary in shape, size, z-distance, and visual context. Nevertheless, the model yielded an R2 of 0.80, and when using effective target width an R2 of 0.88 was achieved.

Inventing new uses for tools: A cognitive foundation for studies on appropriation

Abstract: Appropriation refers to the processes that take place when new uses are invented for tools and when these uses develop into practices and start spreading within a user community. Most research in human–computer interaction and computersupported cooperative work to date has studied this phenomenon from a social sciences approach, thus focusing on the practice side of the phenomenon. This paper addresses appropriation from the other direction, drawing from ecological psychology and focusing on cognitive processes in context. Appropriation from this perspective is understood as an interpretation process in which the user perceives in a tool a new opportunity for action, thus acquiring a new mental usage schema that complements the existing uses. This approach highlights the need to study how schemata are put into use and how they evolve through new interpretations. Ensuing research questions are presented together with three strategies of applying the new approach in system design.