Publication records

Physical Unclonable Functions (PUFs) and, in particular, XOR Arbiter PUFs have gained much research interest as an authentication mechanism for embedded systems. One of the biggest problems of (strong) PUFs is their vulnerability to so called machine learning attacks. In this paper we take a closer look at one aspect of machine learning attacks that has not yet gained the needed attention: the generation of the sub-challenges in XOR Arbiter PUFs fed to the individual Arbiter PUFs. Specifically, we look at one of the most popular ways to generate sub-challenges based on a combination of permutations and XORs as it has been described for the "Lightweight Secure PUF". Previous research suggested that using such a sub-challenge generation increases the machine learning resistance significantly.
Our contribution in the field of sub-challenge generation is three-fold: First, drastically improving attack results by Rührmair et al., we describe a novel attack that can break the Lightweight Secure PUF in time roughly equivalent to an XOR Arbiter PUF without transformation of the challenge input. Second, we give a mathematical model that gives insight into the weakness of the Lightweight Secure PUF and provides a way to study generation of sub-challenges in general. Third, we propose a new, efficient, and cost-effective way for sub-challenge generation that mitigates the attack strategy we used and outperforms the Lightweight Secure PUF in both machine learning resistance and resource overhead.

We study a canonical model of simultaneous price competition between firms that sell a homogeneous good to consumers who are characterized by the number of prices they are exogenously aware of. Our setting subsumes many employed in the literature over the last several decades. We show there is a unique equilibrium if and only if there exist some consumers who are aware of exactly two prices. The equilibrium we derive is in symmetric mixed strategies. Furthermore, when there are no consumers aware of exactly two prices, we show there is an uncountable-infinity of asymmetric equilibria in addition to the symmetric equilibrium. Our results show the paradigm generically produces a unique equilibrium. We also show that the commonly-sought symmetric equilibrium (which also nests the textbookBertrand pure strategy equilibrium as a special case) is robust to perturbations in consumer behaviour, while the asymmetric equilibria are not.

Prior research has shown that immigrants to the U.S. make important contributions to innovation and are more likely than natives to become startup founders. These differences may partly reflect labor market conditions and constraints related to visa regulations, as well as individual attributes such as ability or preferences for risk. Although progress has been made in understanding immigrant entrepreneurs, little attention has been paid to another important part of the entrepreneurial workforce–startup employees who “join” founders in their entrepreneurial efforts. In this paper, we draw on unique longitudinal data from over 5,600 foreign and native STEM PhD students at U.S. research universities to examine entrepreneurial characteristics and career preferences prior to graduation, as well as founding and employment outcomes after graduation. First, we find that foreign PhD students differ from native PhD students with respect to individual characteristics typically associated with entrepreneurship such as risk tolerance, a preference for autonomy, and interest in commercialization. Second, foreign PhD students are more likely to express intentions to become a founder or a startup employee prior to graduation. Third, despite their entrepreneurial career interests, foreign PhDs are less likely to become founders or startup employees in their first industry job after graduation. More nuanced analyses reveal that these patterns hold primarily for foreign PhDs from China and India, while foreign PhDs from Western countries are similar to native PhDs with respect to both career interests and employment outcomes. These empirical patterns call for future research on the drivers of entrepreneurial career preferences among different parts of the foreign doctorate workforce, but also on the facilitators or constraints foreign STEM workers face in realizing their entrepreneurial career aspirations.

The public hearing of the Digital Agenda Committee on the topic of "IT security of hardware and software as a precondition for digital sovereignty" on Wednesday, December 11, 2019, analyzed how citizens, companies, but also public administration organizations in Germany are positioned with regard to digital sovereignty . The Committee led by Hansjörg Durz (CDU/CSU) focused primarily on the current state of Germany's IT infrastructure and governance, the need for legislative action, and security gaps.
In her statement, Isabel Skierka gives an assessment of Germany's industrial policy position in the field of digital technologies and the IT security situation and recommendations for strengthening digital sovereignty and IT security at the national and European level.

[Wie die Bürger, Unternehmen, aber auch die Verwaltung in Deutschland hinsichtlich der digitalen Souveränität aufgestellt sind, dazu gaben die Sachverständigen bei einer öffentlichen Anhörung des Ausschusses Digitale Agenda zum Thema „IT-Sicherheit von Hard- und Software als Voraussetzung für Digitale Souveränität“ am Mittwoch, 11. Dezember 2019, unterschiedliche Einschätzungen ab. Bei der Expertenbefragung unter Leitung von Hansjörg Durz (CDU/CSU) ging es vor allem um den Ist-Zustand der IT-Struktur Deutschlands, gesetzgeberischen Handlungsbedarf und Sicherheitslücken.
In ihrer Stellungnahme gibt Isabel Skierka eine Einsch¨ätzung zur industriepolitischen Stellung Deutschlands im Bereich digitaler Technologien sowie der IT-Sicherheitslage und Empfehlungen für die Stärkung digitaler Souveränität und der IT-Sicherheit auf nationaler und europäischer Ebene.]

This paper analyzes the effect that the U.S. Supreme Court's landmark decision on Citizens United vs. FEC had on corporate political activism. The decision opened the door for corporate treasuries to engage in independent political spending. Politically connected firms have lower announcement returns at the ruling than non-connected firms. The estimates suggest that the value of a political connection decreases by $6.9 million. To evaluate the effect of Citizens United on corporate political activism, we explore the fact that Citizens United also lifts bans on independent political spending in states where such bans existed. After the ruling, firms headquartered in states where bans are lifted have fewer state-level connections relative to firms in other states. Overall, our evidence supports the hypothesis that independent political spending crowds out political connections. We do not find any significant crowding-out effects of independent political expenditures on lobbying activity, executive contributions, and political action committees (PAC) contributions.

With permission of Elsevier

Research has shown that hiring R&D scientists from competitors fosters organizational learning. We examine whether hiring scientists who have many collaborative ties with the hiring firm prior to the mobility event produces different learning outcomes than hiring scientists who have few or no such ties. We theorize that prior ties reduce explorative learning and increase exploitative learning. From our arguments we also derive other testable implications. Namely, we posit that prior ties lead the hiring firm to focus on that part of a new hire’s knowledge with which they are already familiar and that they help appropriate the new hire’s newly generated knowledge. At the same time, prior ties induce new hires to search locally within the hiring firm’s knowledge base and also to produce more incremental, lower-impact innovations. Using data on R&D scientists’ mobility in the Electronics and Electrical Goods industry, we find broad support for our hypotheses. Our results extend our theoretical understanding of learning-by-hiring processes and bear practical managerial implications.

With permission of SAGE Publishing