Bitcoin Transaction Malleability and MtGox

In Bitcoin, transaction malleability describes the fact that the signatures that prove the ownership of bitcoins being transferred in a transaction do not provide any integrity guarantee for the signatures themselves. This allows an attacker to mount a malleability attack in which it intercepts, modifies, and rebroadcasts a transaction, causing the transaction issuer to believe that the original transaction was not confirmed. In February 2014 MtGox, once the largest Bitcoin exchange, closed and filed for bankruptcy claiming that attackers used malleability attacks to drain its accounts. In this work we use traces of the Bitcoin network for over a year preceding the filing to show that, while the problem is real, there was no widespread use of malleability attacks before the closure of MtGox

Photoinitiated Curing of Multifunctional Monomers

Radiation curing is being increasingly used in advanced technology applications, owing to its distinct advantages, mainly its great speed, selective cure and 100% solid formulation. Under intense UV or laser irradiation, the polymerization of multiacrylate monomers was shown to proceed extensively in a fraction of a second. The kinetics of these ultrafast reactions was studied quantitatively by means of the newly developed real-time infrared (RTIR) photo-spectroscopy. From the conversion vs. time curves recorded, the efficiency of some novel photoinitiators and acrylic monomers has been evaluated in UV-curable resins. The crosslinking-polymerization was found to proceed with long kinetic chains, despite the high initiation rate provided by UV or laser irradiation. The actual rate at which polymer chains are growing has been first determined from the polymerization profile recorded upon pulsed laser exposure. The photocured polymers exhibit remarkable mechanical properties, as well as a great resistance to chemicals, heat and radiation. These characteristics, together with the process facility, account for the wide-spread applications of UV curable resins, in particular as protective coatings to improve the weatherability of polymer materials, such as poly(vinyl chloride). Other applications of laser-induced curing are to be found in stereolithography, optoelectronics, holography, and laser direct imaging

P-hacking in clinical trials and how incentives shape the distribution of results across phases

Clinical research should conform to high standards of ethical and scientific integrity, given that human lives are at stake. However, economic incentives can generate conflicts of interest for investigators, who may be inclined to withhold unfavorable results or even tamper with data in order to achieve desired outcomes. To shed light on the integrity of clinical trial results, this paper systematically analyzes the distribution of p-values of primary outcomes for phase II and phase III drug trials reported to the ClinicalTrials.gov registry. First, we detect no bunching of results just above the classical 5% threshold for statistical significance. Second, a density discontinuity test reveals an upward jump at the 5% threshold for phase III results by small industry sponsors. Third, we document a larger fraction of significant results in phase III compared to phase II. Linking trials across phases, we find that early favorable results increase the likelihood of continuing into the next phase. Once we take into account this selective continuation, we can explain almost completely the excess of significant results in phase III for trials conducted by large industry sponsors. For small industry sponsors, instead, part of the excess remains unexplained

P-hacking in clinical trials and how incentives shape the distribution of results across phases

Clinical research should conform to high standards of ethical and scientific integrity, given that human lives are at stake. However, economic incentives can generate conflicts of interest for investigators, who may be inclined to withhold unfavorable results or even tamper with data in order to achieve desired outcomes. To shed light on the integrity of clinical trial results, this paper systematically analyzes the distribution ofPvalues of primary outcomes for phase II and phase III drug trials reported to the ClinicalTrials.gov registry. First, we detect no bunching of results just above the classical 5% threshold for statistical significance. Second, a density-discontinuity test reveals an upward jump at the 5% threshold for phase III results by small industry sponsors. Third, we document a larger fraction of significant results in phase III compared to phase II. Linking trials across phases, we find that early favorable results increase the likelihood of continuing into the next phase. Once we take into account this selective continuation, we can explain almost completely the excess of significant results in phase III for trials conducted by large industry sponsors. For small industry sponsors, instead, part of the excess remains unexplained

Mind the Mining

In this paper we revisit the mining strategies in proof of work based cryptocurrencies and propose two strategies, we call smart and smarter mining, that in many cases strictly dominate honest mining. In contrast to other known attacks, like selfish mining, which induce zero-sum games among the miners, the strategies proposed in this paper increase miners' profit by reducing their variable costs (i.e., electricity). Moreover, the proposed strategies are viable for much smaller miners than previously known attacks, and surprisingly, an attack performed by one miner is profitable for all other miners as well. While saving electricity power is very encouraging for the environment, it is less so for the coin's security. The smart/smarter strategies expose the coin to under 50\% attacks and this vulnerability might only grow when new miners join the coin as a response to the increase in profit margins induced by these strategies

Experimentelle Evidenz zur Wirkung der Teilnahme an E-Learning-Veranstaltungen auf den Klausurerfolg

In diesem Beitrag wird analysiert, wie sich die Teilnahme an einer Lehrveranstaltung aus dem Bereich des E-Learning auf das Klausurergebnis auswirkt. Der Leistungsunterschied zwischen Teilnehmern und Nichtteilnehmern lasst sich nicht allein auf die Partizipation an der Veranstaltung zuruckfuhren, sondern gibt als Average Treatment Effect (ATE) die durchschnittliche Performance der Lehrveranstaltung hinsichtlich des studentischen Lernerfolgs an. Zur Kontrolle der Partizipationsneigung wurden die Teilnehmer im Rahmen eines Experiments in zwei Gruppen eingeteilt, denen teilweise unterschiedliche Lehrinhalte vermittelt wurden. Durch den Vergleich der beiden Teilnehmergruppen untereinander konnte der Average Effect of the Treatment on the Treated (ATT) ermittelt werden. Es zeigte sich, dass der Unterschied zwischen den Teilnehmern und den Verweigerern starker ausgeprägt ist, als zwischen den beiden Teilnehmergruppen des Experiments (ATE > ATT). --Klausurerfolg,Veranstaltungsteilnahme,E-Learning

Prozessorganisation in eingebetteten, ubiquitären Rechnersystemen

Ziel dieser Arbeit ist es, die Prozessausführung ubiquitärer Rechnersysteme unter unbekannten, sich zeitlich verändernden Einsatzbedingungen systematisch zu organisieren, um eine verbesserte Informationsverarbeitung ubiquitärer Appliances zu erreichen. Zentraler Beitrag ist die Theorie der kooperativen und kollaborativen Prozessorganisation für eingebettete, ubiquitäre Rechnersysteme. Kooperative und kollaborative Prozesse erreichen eine zeitnahe Datenverarbeitung und bessere Ressourcennutzung