1,720,959 research outputs found
Feasibility and Limitations of Self-Spoofing Attacks on GNSS Signals with Message Authentication
No full textIn recent years, there has been an ever growing dependence on GNSS for applications in sectors ranging from telecommunications, energy transmission and distribution, to financial services and transportation. As this dependence has increased, so too have risks of intentional interference or spoofing of GNSS signals from adversaries with the intent of causing damage or obtaining illegitimate advantage. The growing interest in GNSS has brought the European Union to develop its own system, Galileo, which recently became operational. The GNSS signal generation is based on public parameters, and to the present date none of the systems provides any means to verify its authenticity or cryptographic integrity. To answer the arising concerns about GNSS security, the European Commission has recently announced that Galileo will offer Navigation Message Authentication (NMA) as a protection against falsified signals, i.e., the so called spoofing attacks. In some scenarios, the attacker can be the very owner of the receiving device, that aims, for instance, at deceiving a monitoring system. These attacks, that go under the name of self-spoofing, have thus become a concern for GNSS based applications. Such scenarios represent some of the most demanding requirements for protection against GNSS spoofing. The implementation of NMA techniques serves the purpose of making this kind of attacks more difficult, too. Two representative applications were considered in the definition of a baseline spoofing scenario and its respective assumptions: satellite-based Vessel Monitoring Systems (VMS) and smart digital tachographs. Satellite-based VMS' were introduced to protect fisheries from illegal fishing, using GNSS for enforcement. Requirements for VMS' specify acceptable position errors and associated confidence intervals, the contents and frequency of transmissions to a Fishing Monitoring Centre (FMC) that allow authorities to react in a timely manner to non compliant behaviour. Today, such measures include the use of tamper-resistant hardware and cryptographic mechanisms to provide protection against vessel owners attempting to tamper or interfere with the device; however, it is only a matter of time before malicious owner resort to GNSS spoofing as a threat to the present enforcement mechanism. The return on investment for defeating the VMS and illegally fishing in closed areas can be significant and can substantially outweigh the costs associated with conducting a spoofing attack. Digital tachographs record the activities of professional drivers including rest and driving hours, increasing road safety, ensuring minimum working conditions and guaranteeing fair competition for EU transport companies. An EU regulation prescribes requirements for construction, testing, installation, operation and repair of tachographs and their components addresses the use of GNSS, remote early detection of possible manipulation or misuse, interfaces with intelligent transport systems and security mechanisms. This paper considers as a baseline a GNSS receiver implementing defences based on the utilisation of Galileo Open Service authentication. In terms of fulfilling its primary task of protecting the integrity of the navigation message, a generic NMA scheme might simply be characterized by its key features, including the number of cryptographic bits inserted in the message, the equivalent security of the scheme, and the period of time over which a complete signature is broadcast. The equivalent security of the scheme indicates the difficulty in performing a brute-force attack on the underlying cryptographic primitives. The number of cryptographic bits inserted will directly influence the availability of the scheme, based on the ability of the receiver to correctly recover all of the bits, and is generally proportional to the equivalent security of the scheme. The period over which the data is broadcast will influence the latency experienced by the receiver in asserting the authenticity of the navigation data, and should therefore be commensurate with, and aligned with, the period over which the protected navigation data is broadcast. When considering the indirect use of the NMA data as a means of anti-spoofing, or range protection, one more feature must be considered: the conditional Shannon entropy of the cryptographic data given the previously transmitted messages. If the data are unknown at the time of broadcast, then one might assume that the adversary must first observe the genuine signal, before creating a counterfeit one. The likelihood of an adversary simply guessing the true value of the cryptographic data is related to the number of bits in question, and the a priori probability of guessing each bit. A common measure of this is the Shannon entropy. When the number of bits is high, then it is very unlikely that the adversary can readily produce a counterfeit signal, without first observing the genuine one. Of course, once the genuine signal is observed, a perfect replica can easily be made. This fact constrains somewhat the degrees of freedom of the counterfeit signals, in that they might only be broadcast in delay with respect to the genuine signals. It might be argued that this itself represents some defence against spoofing. This paper aims at evaluating the efficacy of symbol-level techniques for the mitigation of spoofing attacks. The paper will first analyse the state of the art of both GNSS spoofing attacks and anti-spoofing mechanisms. Theoretical and experimental analysis will be presented in order to investigate the possible increase in the complexity that is required for a successful attack, thanks the adoption of NMA, as well as the intrinsic limitations and weaknesses of these techniques
On trading the spreading gain with the coding rate and its application to GNSS data component design
No full textThe ubiquity of global navigation satellite system (GNSS)-based positioning and timing services is often frustrated by the necessity to operate in harsh environments, where the carrier-to-noise ratio is low, and hence, decoding of navigation data and even tracking of an acquired symbol are difficult. We consider the possibility of improving the decoding performance of the GNSS data component by trading the spreading gain against the coding rate. The rationale is that spreading codes can be seen as a form of repetition coding that can be (at least partially) replaced by more robust coding forms to improve robustness to (any form of) noise. This is true both for the classical additive white Gaussian noise channel case and for more realistic GNSS channel formats severely degraded by multiple access interference and near-far effects. By bringing results on finite-block-length channel capacity and coding rates from information/communication theory to the GNSS domain, we are able to establish and discuss the expected performance gap, as well as the limits of such tradeoff
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Enabling Location Based Services with Privacy and Integrity Protection in Untrusted Environments through Blockchain and Secure Computation
No full textPrivacy and integrity preservation of user data is a major challenge in the context of location based services, as the assumption of trusted relationship between the user and the service provider might be too strong. The question is: how to securely collect, store and process position, navigation and timing (PNT) information and/or georeferenced data, assuming that the service provider cannot be trusted? In this work, we propose an architecture that enables LBS with privacy and integrity in untrusted environments, leveraging blockchain and secure computation. We provide mechanisms for sharing and processing PNT information and/or georeferenced data, with a detailed description of the employed cryptographic schemes and algorithms. Furthermore, we provide a validation of the proposed architecture by means of an emulation-based testbed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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