OALib Journal期刊

ISSN: 2333-9721




2015 ( 18 )

2014 ( 11 )

2013 ( 30 )

2012 ( 44 )


匹配条件: “Iosif Androulidakis” ,找到相关结果约290条。
Ciphering Indicator approaches and user awareness
Iosif Androulidakis
Maejo International Journal of Science and Technology , 2012,
Abstract: One of the fundamental mobile phone security problems in GSM is the absence of base station authentication, which allows man-in-the-middle attacks. During such attacks, a third party activates a fake base station, which acts as a bypass to the network, thus switching off the encryption and intercepting the user’s communications. 3G mobile networks enforce mutual authentication but this can be circumvented if the 3G band is jammed by the attacker, forcing the phone to connect using GSM. GSM and newer standards provide a user alert indicating that the encryption has been switched off, which is called a Ciphering Indicator. In the present paper, different approaches followed by various manufacturers concerning the Ciphering Indicator are investigated. A total of 38 different mobile phones ranging from old to new and from simple to smart-phones that were produced by 13 different manufacturers were intercepted using a GSM testing device in order to document their reactions. Four approaches were identified with some manufacturers choosing not to implement the feature at all. It was also found that in the cases in which the feature was actually implemented, no universal indication was used and it was seldom documented in the phones’ manuals. User awareness regarding the Ciphering Indicator and security issues was also investigated via an empirical survey employing more than 7,000 users from 10 countries and was found to be significantly low.
Classification of extensions of principal bundles and transitive Lie groupoids with prescribed kernel and cokernel
Iakovos Androulidakis
Mathematics , 2004, DOI: 10.1063/1.1786349
Abstract: The equivalence of principal bundles with transitive Lie groupoids due to Ehresmann is a well known result. A remarkable generalisation of this equivalence, due to Mackenzie, is the equivalence of principal bundle extensions with those transitive Lie groupoids over the total space of a principal bundle, which also admit an action of the structure group by automorphisms. This paper proves the existence of suitably equivariant transition functions for such groupoids, generalising consequently the classification of principal bundles by means of their transition functions, to extensions of principal bundles by an equivariant form of \v{C}ech cohomology.
Crossed modules and the integrability of Lie brackets
Iakovos Androulidakis
Mathematics , 2005,
Abstract: We show that the integrability obstruction of a transitive Lie algebroid coincides with the lifting obstruction of a crossed module of groupoids associated naturally with the given algebroid. Then we extend this result to general extensions of integrable transitive Lie algebroids by Lie algebra bundles. Such a lifting obstruction is directly related with the classification of extensions of transitive Lie groupoids. We also give a classification of such extensions which differentiates to the classification of transitive Lie algebroids discussed in \cite{KCHM:new}.
On the connection theory of transitive Lie groupoids
Iakovos Androulidakis
Mathematics , 2003,
Abstract: Due to a result by Mackenzie, extensions of transitive Lie groupoids are equivalent to certain Lie groupoids which admit an action of a Lie group. This paper is a treatment of the equivariant connection theory and holonomy of such groupoids, and shows that such connections give rise to the transition data necessary for the classification of their respective Lie algebroids.
What University Students Do (or Don’t) Know about Security in their Mobile Phones
I. Androulidakis,G. Kandus
Telfor Journal , 2011,
Abstract: We surveyed a pool of 433 students at the University of Banja Luka in Bosnia and Herzegovina during April 2010, examining users’ perceptions about mobile phones security. The main research hypothesis validated was that users are unaware of the necessary measures to avoid a possible unauthorized access and/or sensitive data retrieval from their phones and that they lack proper security education. Most of the results proved to be non-country specific, revealing that users feel mobile phone communication is not secure. We further present the results about users’ security practices regarding mobile phone usage.
Mobile Phone Brand Categorization vs. Users’ Security Practices
I. Androulidakis,G. Kandus
Engineering, Technology & Applied Science Research , 2011,
Abstract: In the present paper, we correlated the brand of mobile phone to users’ security practices, statistically processing a large pool of the responses of 7172 students in 17 Universities of 10 Eastern and Southern Europe countries. Users show different behavior in an array of characteristics, according to the brand of the mobile phone they are using. As such, there is a categorization of areas, different for each brand, where users are clearly lacking security mind, possibly due to lack of awareness. Such a categorization can help phone manufacturers enhance their mobile phones in regards to security, preferably transparently for the user.
The analytic index of elliptic pseudodifferential operators on a singular foliation
Iakovos Androulidakis,Georges Skandalis
Mathematics , 2010,
Abstract: In previous papers (arxiv:math/0612370 and arxiv:0909.1342) we defined the C*-algebra and the longitudinal pseudodifferential calculus of any singular foliation (M,F). Here we construct the analytic index of an elliptic operator as a KK-theory element, and prove that the same element can be obtained from an "adiabatic foliation" TF on $M \times \R$, which we introduce here.
The Baum-Connes conjecture for singular foliations
Iakovos Androulidakis,Georges Skandalis
Mathematics , 2015,
Abstract: We consider singular foliations whose holonomy groupoid may be nicely decomposed using Lie groupoids (of unequal dimension). We show that the Baum-Connes conjecture can be formulated in this setting. This conjecture is shown to hold under assumptions of amenability. We examine several examples that can be described in this way and make explicit computations of their K-theory.
Holonomy transformations for singular foliations
Iakovos Androulidakis,Marco Zambon
Mathematics , 2012,
Abstract: In order to understand the linearization problem around a leaf of a singular foliation, we extend the familiar holonomy map from the case of regular foliations to the case of singular foliations. To this aim we introduce the notion of holonomy transformation. Unlike the regular case, holonomy transformations can not be attached to classes of paths in the foliation, but rather to elements of the holonomy groupoid of the singular foliation. This assignment is injective. Holonomy transformations allow us to link the linearization problem with the compactness of the isotropy group of the holonomy groupoid, as well as with the linearization problem for proper Lie groupoids.
The holonomy groupoid of a singular foliation
Iakovos Androulidakis,Georges Skandalis
Mathematics , 2006,
Abstract: We construct the holonomy groupoid of any singular foliation. In the regular case this groupoid coincides with the usual holonomy groupoid of Winkelnkemper (1983); the same holds in the singular cases of Bigonnet and Pradines (1985) and Debord (2001), which from our point of view can be thought of as being "almost regular". In the general case, the holonomy groupoid can be quite an ill behaved geometric object. On the other hand it often has a nice longitudinal smooth structure. Nonetheless, we use this groupoid to generalize to the singular case Connes' construction of the C*-algebra of the foliation. We also outline the construction of a longitudinal pseudo-differential calculus; the analytic index of a longitudinally elliptic operator takes place in the K-theory of our C*-algebra. In our construction, the key notion is that of a bi-submersion which plays the role of a local Lie groupoid defining the foliation. Our groupoid is the quotient of germs of these bi-submersions with respect to an appropriate equivalence relation.

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