Shake well before use: Authentication based on Accelerometer Data

Small, mobile devices without user interfaces, such as Bluetooth headsets, often need to communicate securely over wireless networks. Active attacks can only be prevented by authenticating wireless communication, which is problematic when devices do not have any a priori information about each other. We introduce a new method for device-to-device authentication by shaking devices together. This paper describes two protocols for combining cryptographic authentication techniques with known methods of accelerometer data analysis to the effect of generating authenticated, secret keys. The protocols differ in their design, one being more conservative from a security point of view, while the other allows more dynamic interactions. Three experiments are used to optimize and validate our proposed authentication method

Non-Geometric Vacua of the Spin(32)/Z2\mathbf{\text{Spin}(32)/\mathbb Z_2} Heterotic String and Little String Theories

We study a class of 6d $\mathcal{N}=(1,0)$ non-geometric vacua of the $\text{Spin}(32)/\mathbb Z_2$ heterotic string which can be understood as fibrations of genus-two curves over a complex one-dimensional base. The 6d $\mathcal{N}=(1,0)$ theories living on the defects that arise when the genus-two fiber degenerates at a point of the base are analyzed by dualizing to F-theory on elliptic K3-fibered non-compact Calabi-Yau threefolds. We consider all possible degenerations of genus-two curves and systematically attempt to resolve the singularities of the dual threefolds. As in the analogous non-geometric vacua of the $E_8\times E_8$ heterotic string, we find that many of the resulting dual threefolds contain singularities which do not admit a crepant resolution. When the singularities can be resolved crepantly, we determine the emerging effective theories which turn out to be little string theories at a generic point on their tensor branch. We also observe a form of duality in which theories living on distinct defects are the same.Comment: 39 pages, 3 figures, and 6 table

Non-Fermi liquid behavior in transport across carbon nanotube quantum dots

A low energy-theory for non-linear transport in finite-size single-wall carbon nanotubes, based on a microscopic model for the interacting pz electrons and successive bosonization, is presented. Due to the multiple degeneracy of the energy spectrum diagonal as well as off-diagonal (coherences) elements of the reduced density matrix contribute to the nonlinear transport. A four-electron periodicity with a characteristic ratio between adjacent peaks, as well as nonlinear transport features, in quantitative agreement with recent experiments, are predicted.Comment: 5 pages, 3 figure

Pseudo-spin-dependent scattering in carbon nanotubes

The breaking of symmetry is the ground on which many physical phenomena are explained. This is important in particular for bipartite lattice structure as graphene and carbon nanotubes, where particle-hole and pseudo-spin are relevant symmetries. Here we investigate the role played by the defect-induced breaking of these symmetries in the electronic scattering properties of armchair single-walled carbon nanotubes. From Fourier transform of the local density of states we show that the active electron scattering channels depend on the conservation of the pseudo-spin. Further, we show that the lack of particle-hole symmetry is responsible for the pseudo-spin selection rules observed in several experiments. This symmetry breaking arises from the lattice reconstruction appearing at defect sites. Our analysis gives an intuitive way to understand the scattering properties of carbon nanotubes, and can be employed for newly interpret several experiments on this subject. Further, it can be used to design devices such as pseudo-spin filter by opportune defect engineering

Acoustic Integrity Codes: Secure Device Pairing Using Short-Range Acoustic Communication

Secure Device Pairing (SDP) relies on an out-of-band channel to authenticate devices. This requires a common hardware interface, which limits the use of existing SDP systems. We propose to use short-range acoustic communication for the initial pairing. Audio hardware is commonly available on existing off-the-shelf devices and can be accessed from user space without requiring firmware or hardware modifications. We improve upon previous approaches by designing Acoustic Integrity Codes (AICs): a modulation scheme that provides message authentication on the acoustic physical layer. We analyze their security and demonstrate that we can defend against signal cancellation attacks by designing signals with low autocorrelation. Our system can detect overshadowing attacks using a ternary decision function with a threshold. In our evaluation of this SDP scheme's security and robustness, we achieve a bit error ratio below 0.1% for a net bit rate of 100 bps with a signal-to-noise ratio (SNR) of 14 dB. Using our open-source proof-of-concept implementation on Android smartphones, we demonstrate pairing between different smartphone models.Comment: 11 pages, 11 figures. Published at ACM WiSec 2020 (13th ACM Conference on Security and Privacy in Wireless and Mobile Networks). Updated reference

Algebraic Cycles and Local Anomalies in F-Theory

We introduce a set of identities in the cohomology ring of elliptic fibrations which are equivalent to the cancellation of gauge and mixed gauge-gravitational anomalies in F-theory compactifications to four and six dimensions. The identities consist in (co)homological relations between complex codimension-two cycles. The same set of relations, once evaluated on elliptic Calabi-Yau three-folds and four-folds, is shown to universally govern the structure of anomalies and their Green-Schwarz cancellation in six- and four-dimensional F-theory vacua, respectively. We furthermore conjecture that these relations hold not only within the cohomology ring, but even at the level of the Chow ring, i.e. as relations among codimension-two cycles modulo rational equivalence. We verify this conjecture in non-trivial examples with Abelian and non-Abelian gauge groups factors. Apart from governing the structure of local anomalies, the identities in the Chow ring relate different types of gauge backgrounds on elliptically fibred Calabi-Yau four-folds.Comment: 45 page

Hypercharge Flux in IIB and F-theory: Anomalies and Gauge Coupling Unification

We analyse hypercharge flux GUT breaking in F-theory/Type IIB GUT models with regards to its implications for anomaly cancellation and gauge coupling unification. To this aim we exploit the Type IIB limit and consider 7-brane configurations that for the first time are guaranteed to exhibit net hypercharge flux restriction to matter curves. We show that local F-theory models with anomalies of type U(1)_Y-U(1)^2 in the massless spectrum can be consistent only if such additional U(1)s are globally geometrically massive (in the sense that they arise from non-Kahler deformations of the Calabi-Yau four-fold). Further, in such cases of geometrically massive U(1)s hypercharge flux can induce new anomalies of type U(1)_Y^2-U(1) in the massless spectrum, violating constraints in local models forbidding such anomalies. In particular this implies that it is possible to construct models exhibiting a U(1)_{PQ} global symmetry which have hypercharge flux doublet-triplet splitting and no further exotics. We also show that the known hypercharge flux induced splitting of the gauge couplings in IIB models at tree-level can be reduced by a factor of 5 by employing a more F-theoretic twisting of U(1) flux by hypercharge flux bringing it to well within MSSM 2-loop results. In the case of net restriction of hypercharge flux to matter curves this tree-level splitting becomes more involved, is tied to the vacuum expectation values of certain closed-string fields, and therefore gauge coupling unification becomes tied to the question of moduli stabilisation.Comment: 27 pages. v2: Expanded discussion on anomalies and showed that geometrically massive U(1)s of Peccei-Quinn type are compatible with hypercharge flux doublet-triplet splitting with no exotic

Graphene armchair nanoribbon single-electron transistors: The peculiar influence of end states

We present a microscopic theory for interacting graphene armchair nanoribbon quantum dots. Long range interaction processes are responsible for Coulomb blockade and spin-charge separation. Short range ones, arising from the underlying honeycomb lattice of graphene, smear the spin-charge separation and induce exchange correlations between bulk electrons - delocalized on the ribbon - and single electrons localized at the two ends. As a consequence, entangled end-bulk states where the bulk spin is no longer a conserved quantity occur. Entanglement's signature is the occurrence of negative differential conductance effects in a fully symmetric set-up due to symmetry-forbidden transitions.Comment: 6 pages, 7 figures; version submitted to EP

Higher-Order Risk Preferences – Consequences for Test and Treatment Thresholds and Optimal Cutoffs

Higher-order risk attitudes include risk aversion, prudence, and temperance. This paper analyzes the effects of such preferences on medical test and treatment decisions, represented either by test and treatment thresholds or – if the test characteristics are endogenous – by the optimal cutoff value for testing. For a risk-averse decision maker, treatment is a risk reducing strategy since it prevents the low health outcome that forgoing treatment yields in the sick state. As compared to risk neutrality, risk aversion thus reduces both the test and the treatment threshold and decreases the optimal cutoff. Prudence is relevant if a comorbidity risk applies in the sick state. It leads to even lower thresholds and a lower optimal cutoff. Finally, temperance plays a role if the comorbidity risk is left-skewed. It lowers the thresholds and the optimal cutoff even further. These findings suggest that diagnostics in low prevalence settings (e.g. screening) are considered more beneficial when higher-order risk preferences are taken into account.Medical decision making; diagnostic risk; test and treatment thresholds; optimal cutoff; risk aversion; prudence

Private Regulation by Platform Operators – Implications for Usage Intensity

Platforms operators act as private regulators to increase usage and maximize profits. Their goals depend on the development of the platform: overcoming the chicken-egg problem early on requires attracting platform participants while quality becomes more important later on. Private regulators influence third-party business models, entry barriers, and usage intensity. We analyze how drivers of usage intensity on Facebook’s application platform were affected by a policy change that increased quality incentives for applications. This change led to the number of installations of each application becoming less important, applications in more concentrated sub-markets achieving higher usage, and applications staying attractive for longer