4,327 research outputs found
Optimization of the ROCA (CVE-2017-15361) Attack
2017. aastal avastasid Tšehhi teadlased Infineoni loodud RSA võtmete genereerimis algoritmist haavatavuse CVE-2017-15361 (ROCA rünnak). Leiti, et Infineoni algoritmiga genereeritud 2048-bitiseid võtmeid on võimalik faktoriseerida halvimal juhul kõigest 140.8 CPU aastaga. Antud algortimi kasutades olid genereeritud võtmed 750 000 Eesti ID-kaardi jaoks. Selle magistritöö raames implementeeriti ROCA rünnak ning genereeritud võtmeid ja haavatavaid kiipkaarte analüüsides loodi rünnakust uus, optimiseeritud versioon, mille abil on võimalik sooritada rünnak 140.8 aasta asemel 35.2 CPU aastaga 90% võtmete puhul ning 70.4 aastaga ülejäänud võtmetel. Lisaks loodi paralleliseeritud versioon rünnakust kasutades teadusarvutuste klastrit (HPC).In 2017, Czech researchers found the vulnerability CVE-2017-15361 (the ROCA attack) in Infineon's proprietary RSA key generation algorithm. The researchers found that 2048-bit RSA key can be factored in only 140.8 CPU-years in the worst case scenario. The algorithm turned out to be used by 750 000 Estonian ID-cards. In this thesis, we implemented the ROCA attack and, based on the properties observed from the keys generated by the affected smartcards, found further optimizations which allow to improve the original attack from 140.8 CPU-years to 35.2 CPU-years for 90% of the keys and 70.4 CPU-years for the remaining 10% of the keys. As additional contribution, we provide a parallelized version of the attack that can be executed on an HPC
A Multistage Method for SCMA Codebook Design Based on MDS Codes
Sparse Code Multiple Access (SCMA) has been recently proposed for the future
generation of wireless communication standards. SCMA system design involves
specifying several parameters. In order to simplify the procedure, most works
consider a multistage design approach. Two main stages are usually emphasized
in these methods: sparse signatures design (equivalently, resource allocation)
and codebook design. In this paper, we present a novel SCMA codebook design
method. The proposed method considers SCMA codebooks structured with an
underlying vector space obtained from classical block codes. In particular,
when using maximum distance separable (MDS) codes, our proposed design provides
maximum signal-space diversity with a relatively small alphabet. The use of
small alphabets also helps to maintain desired properties in the codebooks,
such as low peak-to-average power ratio and low-complexity detection.Comment: Submitted to IEEE Wireless Communication Letter
The importance of inversion disorder in the visible light induced persistent luminescence in Cr doped ABO (A = Zn or Mg and B = Ga or Al)
Cr doped spinel compounds ABO with A=Zn, Mg and B=Ga, Al
exhibit a long near infrared persistent luminescence when excited with UV or
X-rays. In addition, persistent luminescence of ZnGaO and to a lesser
extent MgGaO, can also be induced by visible light excitation via
A T transition of Cr, which makes these
compounds suitable as biomarkers for in vivo optical imaging of small animals.
We correlate this peculiar optical property with the presence of antisite
defects, which are present in ZnGaO and MgGaO. By using X-ray
absorption fine structure (XAFS) spectroscopy, associated with electron
paramagnetic resonance (EPR) and optical emission spectroscopy, it is shown
that an increase in antisite defects concentration results in a decrease in the
Cr-O bond length and the octahedral crystal field energy. A part of the defects
are in the close environment of Cr ions, as shown by the increasing
strain broadening of EPR and XAFS peaks observed upon increasing antisite
disorder. It appears that ZnAlO, which exhibits the largest crystal
field splitting of Cr and the smallest antisite disorder, does not show
considerable persistent luminescence upon visible light excitation as compared
to ZnGaO and MgGaO. These results highlight the importance of
Cr ions with neighboring antisite defects in the mechanism of persistent
luminescence exhibited by Cr doped ABO spinel compounds.Comment: 10 pages + supplementary (available on request
UV Light Reveals the Diversity of Jurassic Shell Colour Patterns: Examples from the Cordebugle Lagerstätte (Calvados, France)
Viewed under UV light the diverse and exceptionally well-preserved molluscs from the Late Jurassic Cordebugle Konservat Lagerstätte (Calvados, Normandy, France) reveal fluorescent fossil shell colour patterns predating the oldest previously known instance of such patterns by 100 Myr. Evidently, residual colour patterns are observable in Mesozoic molluscs by application of this non-destructive method, provided the shells are not decalcified or recrystallized. Among 46 species which are assigned to twelve gastropod families and eight bivalve families, no less than 25 species yielded positive results. Out of nine colour pattern morphologies that have been distinguished six occur in gastropods and three in bivalves. The presence of these variant morphologies clearly indicates a significant pre-Cenozoic diversification of colour patterns, especially in gastropods. In addition, the occurrence of two distinct types of fluorescence highlights a major difference in the chemical composition of the pigments involved in colour pattern formation in gastropods. This discovery enables us to discriminate members of higher clades, i.e. the Vetigastropoda emitting red fluorescence from the Caenogastropoda and Heterobranchia emitting whitish-beige to yellow fluorescence. Consequently, fluorescent colour patterns may help to allocate part of the numerous enigmatic Mesozoic gastropod taxa to their correct systematic position
Adsorption behavior of conjugated {C}3-oligomers on Si(100) and HOPG surfaces
A pi-conjugated {C}3h-oligomer involving three dithienylethylene branches
bridged at the meta positions of a central benzenic core has been synthesized
and deposited either on the Si(100) surface or on the HOPG surface. On the
silicon surface, scanning tunneling microscopy allows the observation of
isolated molecules. Conversely, by substituting the thiophene rings of the
oligomers with alkyl chains, a spontaneous ordered film is observed on the HOPG
surface. As the interaction of the oligomers is different with both surfaces,
the utility of the Si(100) surface to characterize individual oligomers prior
to their use into a 2D layer is discussed
YBCO Transition Edge Sensors Used For Very Low Noise Thermal Control
In electrically substituted radiometers, the ultra low noise control of the
temperature is required. In this framework, we present results dedicated to the
temperature regulation of copper plates, 3 cm diameter and 1 mm thick, using
YBa2Cu3O7-d (YBCO) transition edge sensors (TES). One of the TES was used as
the active thermometer of the temperature control unit, whereas the two others
measured the plate temperature behavior. Two heating resistors were wound along
a spiral pattern, just underneath the copper plate, to minimize the heating
delay. The correlation between the two TES was clearly highlighted by applying
a small heat perturbation through the second distributed resistor, the path of
which closely follows that of the main resistor. Calibrated temperature
oscillations of 30 microK rms at 10mHz together with spectral analysis were
measured and a temperature resolution in the range of a few microK rms was
achieved.Comment: 6 pages, ASC 2002 (Applied Superconductivity Conference), Houston, TX
USA (Aout 2002): Oral contribution, to be published in IEEE Trans. Appl.
Supercond. June 200
Statactivism: Forms of action between disclosure and affirmation
This article introduces the special issue on statactivism, a particular form of action within the repertoire used by contemporary social movements: the mobilization of statistics. Traditionally, statistics has been used by the worker movement within the class conflicts. But in the current configuration of state restructuring, new accumulation regimes, and changes in work organization in capitalists societies, the activist use of statistics is moving. This first article seeks to show the use of statistics and quantification in contentious performances connected with state restructuring, main transformations of the varieties of capitalisms, and changes in work organization regimes. The double role of statistics in representing as well as criticizing reality is considered. After showing how important statistical tools are in producing a shared reading of reality, we will discuss the two main dimensions of statactivism – disclosure and affirmation. In other words, we will see the role of stat-activists in denouncing a certain state of reality, and then the efforts to use statistics in creating equivalency among disparate conditions and in cementing emerging social categories. Finally, we present the main contributions of the various research papers in this special issue regarding the use of statistics as a form of action within a larger repertoire of contentious action. Six empirical papers focus on statactivism against the penal machinery in the early 1970s (Grégory Salle), on the mobilisation on the price index in Guadalupe in 2009 (Boris Samuel), and in Argentina in 2007 (Celia Lury and Ana Gross), on the mobilisations of experts to consolidate a link between working conditions and health issues (Marion Gilles), on the production of activity data for disability policy in France (Pierre-Yves Baudot), and on the use of statistics in social mobilizations for gender equality (Eugenia De Rosa). Alain Desrosières wrote the last paper, coping with mobilizations proposing innovations in the way of measuring inflation, unemployment, poverty, GDP, and climate change. This special issue is dedicated to him, in order to honor his everlasting intellectual legac
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