Demo: Linux Goes Apple Picking: Cross-Platform Ad hoc Communication with Apple Wireless Direct Link

Apple Wireless Direct Link (AWDL) is a proprietary and undocumented wireless ad hoc protocol that Apple introduced around 2014 and which is the base for applications such as AirDrop and AirPlay. We have reverse engineered the protocol and explain its frame format and operation in our MobiCom '18 paper "One Billion Apples' Secret Sauce: Recipe of the Apple Wireless Direct Link Ad hoc Protocol." AWDL builds on the IEEE 802.11 standard and implements election, synchronization, and channel hopping mechanisms on top of it. Furthermore, AWDL features an IPv6-based data path which enables direct communication. To validate our own work, we implement a working prototype of AWDL on Linux-based systems. Our implementation is written in C, runs in userspace, and makes use of Linux's Netlink API for interactions with the system's networking stack and the pcap library for frame injection and reception. In our demonstrator, we show how our Linux system synchronizes to an existing AWDL cluster or takes over the master role itself. Furthermore, it can receive data frames from and send them to a MacBook or iPhone via AWDL. We demonstrate the data exchange via ICMPv6 echo request and replies as well as sending and receiving data over a TCP connection.Comment: The 24th Annual International Conference on Mobile Computing and Networking (MobiCom '18

Comparison of synthetic maps from truncated jet-formation models with YSO jet observations

(abridged) Significant progress has been made in the last years in the understanding of the jet formation mechanism through a combination of numerical simulations and analytical MHD models for outflows characterized by the symmetry of self-similarity. In a previous article we introduced models of truncated jets from disks, i.e. evolved in time numerical simulations based on a radially self-similar MHD solution, but including the effects of a finite radius of the jet-emitting disk and thus the outflow. These models need now to be compared with available observational data. A direct comparison of the results of combined analytical theoretical models and numerical simulations with observations has not been performed as yet. In order to compare our models with observed jet widths inferred from recent optical images taken with HST and AO observations, we use a new set of tools to create emission maps in different forbidden lines, from which we determine the jet width as the FWHM of the emission. It is shown that the untruncated analytical disk outflow solution considered here cannot fit the small jet widths inferred by observations of several jets. Various truncated disk-wind models are examined, whose extracted jet widths range from higher to lower values compared to the observations. Thus we can fit the observed range of jet widths by tuning our models. We conclude that truncation is necessary to reproduce the observed jet widths and our simulations limit the possible range of truncation radii. We infer that the truncation radius, which is the radius on the disk mid-plane where the jet-emitting disk switches to a standard disk, must be between around 0.1 up to about 1 AU in the observed sample for the considered disk-wind solution. One disk-wind simulation with an inner truncation radius at about 0.11 AU also shows potential for reproducing the observations, but a parameter study is needed.Comment: accepted for publication in A & A, 14 pages, 21 figure

Towards a self-consistent relativistic model of the exterior gravitational field of rapidly rotating neutron stars

We present a self-consistent, relativistic model of rapidly rotating neutron stars describing their exterior gravitational field. This is achieved by matching the new solution of Einstein's field equations found by Manko et al. (2000) and the numerical results for the interior of neutron stars with different equations of state calculated by Cook et al. (1994). This matching process gives constraints for the choice of the five parameters of the vacuum solution. Then we investigate some properties of the gravitational field of rapidly rotating neutron stars with these fixed parameters.Comment: 11 pages, 18 figures, accepted for publication in MNRA

Radiation hydrodynamics integrated in the code PLUTO

The transport of energy through radiation is very important in many astrophysical phenomena. In dynamical problems the time-dependent equations of radiation hydrodynamics have to be solved. We present a newly developed radiation-hydrodynamics module specifically designed for the versatile MHD code PLUTO. The solver is based on the flux-limited diffusion approximation in the two-temperature approach. All equations are solved in the co-moving frame in the frequency independent (grey) approximation. The hydrodynamics is solved by the different Godunov schemes implemented in PLUTO, and for the radiation transport we use a fully implicit scheme. The resulting system of linear equations is solved either using the successive over-relaxation (SOR) method (for testing purposes), or matrix solvers that are available in the PETSc library. We state in detail the methodology and describe several test cases in order to verify the correctness of our implementation. The solver works in standard coordinate systems, such as Cartesian, cylindrical and spherical, and also for non-equidistant grids. We have presented a new radiation-hydrodynamics solver coupled to the MHD-code \PLUTO that is a modern, versatile and efficient new module for treating complex radiation hydrodynamical problems in astrophysics. As test cases, either purely radiative situations, or full radiation-hydrodynamical setups (including radiative shocks and convection in accretion discs) have been studied successfully. The new module scales very well on parallel computers using MPI. For problems in star or planet formation, we have added the possibility of irradiation by a central source.Comment: 13 pages, 11 figures, accepted by Astronomy & Astrophysic

Formation and Propagation of Jets in Symbiotic Stars

Although jets are ubiquitous phenomena in many different astrophysical objects, their formation is relatively unclear. The necessary components seem to be well known and identical in all objects. A more careful investigation of one certain class of objects should promise new insights also for the mechanisms in the other classes. From the observational point of view, one needs observations with a high spatial resolution and kinematic informations from regions as near as possible to the jet source. These points make the class of symbiotic stars, interacting binaries consisting of a cool red giant (RG) and a white dwarf (WD), ideal testbeds. In the first part of this thesis the propagation of the jet in the unique system MWC 560, where the jet axis is practically parallel to the line of sight, is investigated numerically. This special orientation provides the opportunity to observe the outflowing gas as line absorption in the source spectrum. Therefore MWC 560 can be used to probe the short term evolution and the propagation of the gas outflow in jets from WD. We present model results concerning the structure and emission of the jets and theoretical absorption line profile which are compared with observations of MWC 560. In the second part, we focus on the formation and collimation process of jets from WD. We mainly investigate the effect of a solid surface of the central, accreting object and of the creation of a boundary layer around it

DEMO: BTLEmap: Nmap for Bluetooth Low Energy

The market for Bluetooth Low Energy devices is booming and, at the same time, has become an attractive target for adversaries. To improve BLE security at large, we present BTLEmap, an auditing application for BLE environments. BTLEmap is inspired by network discovery and security auditing tools such as Nmap for IP-based networks. It allows for device enumeration, GATT service discovery, and device fingerprinting. It goes even further by integrating a BLE advertisement dissector, data exporter, and a user-friendly UI, including a proximity view. BTLEmap currently runs on iOS and macOS using Apple's CoreBluetooth API but also accepts alternative data inputs such as a Raspberry Pi to overcome the restricted vendor API. The open-source project is under active development and will provide more advanced capabilities such as long-term device tracking (in spite of MAC address randomization) in the future.Comment: 13th ACM Conference on Security and Privacy in Wireless and Mobile Network

The bipolar jet of the symbiotic star R Aquarii: A study of its morphology using the high-resolution HST WFC3/UVIS camera

R Aqr is a symbiotic binary system consisting of a Mira variable with a pulsation period of 387 days and a hot companion which is presumably a white dwarf with an accretion disk. This binary system is the source of a prominent bipolar gaseous outflow. We use high spatial resolution and sensitive images from the Hubble Space Telescope to identify and investigate the different structural components that form the complex morphology of the R Aqr jet . Methods. We present new high-resolution HST WFC3/UVIS narrow-band images of the R Aqr jet obtained in 2013/14 in the light of the [OIII] 5007, [OI] 6300, [NII] 6583, and Ha emission lines. These images also allow us to produce detailed maps of the jet flow in several line ratios such as [OIII]/[OI] and [NII]/[OI] which are sensitive to the outflow temperature and its hydrogen ionisation fraction. The new emission maps together with archival HST data are used to derive and analyse the proper motion of prominent emitting features which can be traced over 20 years with the HST observations. The images reveal the fine gas structure of the jet out to distances of a few ten arcseconds from the central region, as well as in the innermost region, within a few arcseconds around the stellar source. They reveal for the first time the straight highly-collimated jet component which can be traced to up to 900 AU in the NE direction. Images in [OIII], [OI], and [NII] clearly show a helical pattern in the jet beams which may derive from the small-scale precession of the jet. The highly-collimated jet is accompanied by a wide opening angle outflow which is filled by low excitation gas. The position angles of the jet structures as well as their opening angles are calculated. Our measurements of the proper motions of some prominent emission knots confirm the scenario of gas acceleration during the propagation of the outflow.Comment: 15 pages, 7 figure

One Billion Apples' Secret Sauce: Recipe for the Apple Wireless Direct Link Ad hoc Protocol

Apple Wireless Direct Link (AWDL) is a proprietary and undocumented IEEE 802.11-based ad hoc protocol. Apple first introduced AWDL around 2014 and has since integrated it into its entire product line, including iPhone and Mac. While we have found that AWDL drives popular applications such as AirPlay and AirDrop on more than one billion end-user devices, neither the protocol itself nor potential security and Wi-Fi coexistence issues have been studied. In this paper, we present the operation of the protocol as the result of binary and runtime analysis. In short, each AWDL node announces a sequence of Availability Windows (AWs) indicating its readiness to communicate with other AWDL nodes. An elected master node synchronizes these sequences. Outside the AWs, nodes can tune their Wi-Fi radio to a different channel to communicate with an access point, or could turn it off to save energy. Based on our analysis, we conduct experiments to study the master election process, synchronization accuracy, channel hopping dynamics, and achievable throughput. We conduct a preliminary security assessment and publish an open source Wireshark dissector for AWDL to nourish future work.Comment: The 24th Annual International Conference on Mobile Computing and Networking (MobiCom '18