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Slamanig D.,Carinthia University of Applied Sciences
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2011

Anonymous authentication apparently seems to be an oxymoron, since authentication is the task of proving one's identity to another party and anonymity is concerned with hiding one's identity. However, there are quite different constructions like ring [5] and group signatures [1] to solve this task. We are focusing on anonymous authentication protocols using public-key encryption schemes as their underlying building block, which, in contrast to the aforementioned, do receive only little attention. However, such anonymous authentication protocols are much simpler than other constructions and they can provide significant advantages over the aforementioned approaches. Firstly, they are fully compatible with deployed public-key infrastructures (PKIs) and thus can be adopted very easily. Secondly, such schemes enjoy an "ad-hoc" character and thus do not require involved registration or setup procedures. This is especially advantageous in dynamic environments, e.g. when users dynamically join and leave the group of authorized users. In this context existing primitives like group signatures to date lack of an efficient and practical solution. Furthermore, the "ad-hoc" character of these schemes allows users to flexibly choose their level of anonymity, i.e. the size of the group (anonymity set), for the sake of improved efficiency and additionally do not suffer from linear complexity such as ring signatures. © 2011 Springer-Verlag. Source

Bouchachia A.,Klagenfurt University | Prossegger M.,Carinthia University of Applied Sciences
Applied Soft Computing Journal | Year: 2011

Hybrid approaches are often recommended for dealing in an efficient manner with complex problems that require considerable computational time. In this study, we follow a similar approach consisting of combining spectral clustering and ant colony optimization in a two-stage algorithm for the purpose of efficiently solving the Steiner tree problem in large graphs. The idea of the two-stage approach, called ESC-IAC, is to apply a divide-and-conquer strategy which consists of breaking down the problem into sub-problems to find local solutions before combining them. In the first stage, graph segments (clusters) are generated using an ensemble spectral clustering method for enhancing the quality; whereas in the second step, parallel independent ant colonies are implemented to find local and global minima of the Steiner tree. To illustrate the efficiency and accuracy, ESC-IAC is applied in the context of a geographical application relying on real-world as well as artificial benchmarks. © 2011 Elsevier B.V. All rights reserved. Source

Tributsch H.,Carinthia University of Applied Sciences
Physica Status Solidi (A) Applications and Materials Science | Year: 2014

Nature looks back at a long evolution of successful energy materials, which have especially been adapted to deal with small energy quantities from the environment. Few basic organic materials, such as cellulose, chitin and keratin have been selected and highly diversified, mostly via nano-and micro-technological modifications. A similar strategy occurred with inorganic compounds, such as silica, hydroxyapatite, or calcium carbonate. Others were precisely tailored to support well-defined strategies such as, for example, the kinetic solar cell principle, ionic energy converters, water splitting, quantum light collection, encapsulation, or fire resistance. In an attempt to learn from nature relevant aspects of biological energy conversion, relevant materials are analyzed and discussed. By looking at them we can more critically judge present technical-industrial developments and recognize unexploited energy and material technologies. This is a tree-fungus of unidentified name growing on hazelnut. With chitin in its cell walls, it is a marvel in enzyme mediated energy catalysis for converting and upgrading of polysaccharides including cellulose. Its astonishing surface structure is reflecting self-organization with fractal, self-similar patterns. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Slamanig D.,Carinthia University of Applied Sciences
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2012

In this paper we are interested in privacy preserving discretionary access control (DAC) for outsourced storage such as increasingly popular cloud storage services. Our main goal is to enable clients, who outsource data items, to delegate permissions (read, write, delete) to other clients such that clients are able to unlinkably and anonymously perform operations on outsourced data items when holding adequate permission. In contrast to recent approaches based on oblivious RAM, oblivious transfer combined with anonymous credentials or attribute based encryption, we propose a solution based on dynamic accumulators. In doing so, our approach naturally reflects the concept of access control lists (ACLs), which are a popular means to implement DAC. © 2012 Springer-Verlag. Source

Slamanig D.,Carinthia University of Applied Sciences
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2012

In this paper we introduce anonymous yet authorized and bounded cloud resource schemes. Contrary to many other approaches to security and privacy in the cloud, we aim at hiding behavioral information, i.e. consumption patterns, of users consuming their cloud resources, e.g. CPU time or storage space, from a cloud provider. More precisely, users should be able to purchase a contingent of resources from a cloud provider and be able to anonymously and unlinkably consume their resources till their limit (bound) is reached. Furthermore, they can also reclaim these resources back anonymously, e.g. if they delete some stored data. We present a definition of such schemes along with a security model and present an instantiation based on Camenisch-Lysyanskaya signatures. Then, we extend the scheme to another scheme providing even more privacy for users, i.e. by even hiding the issued resource limit (bound) during interactions and thus providing full anonymity to users, and present some useful extensions for both schemes. We also support our theoretical claims with experimental results obtained from an implementation that show the practicality of our schemes. © 2012 Springer-Verlag. Source

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