Riesen, Kaspar
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Riesen, Kaspar
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- PublikationSketch Based User Authentication with a Novel String Edit Distance Model(ICEE, 05.09.2016) Riesen, Kaspar; Hanne, Thomas; Schmidt, Rainer; Riesen, Kaspar [in: IEEE Transactions on Systems, Man and Cybernetics: Systems]The vast majority of user authentication in digital applications is based on alphanumeric passwords. Yet, due to severe problems that might arise with this approach, various efforts have been made in the last decade to replace this authentication paradigm. One candidate for the prospective paradigm shift might be found in the field of graphical passwords. The present paper introduces a novel framework for user authentication based on freehand sketches. The basic idea is that during the registration phase a user draws an arbitrary sketch in a specific drawing canvas (rather than typing a password). Registered users can then be authenticated whenever they are able to reproduce their personal sketch with sufficient precision. The major challenge of such a system is twofold. First, it has to provide a certain degree of error-tolerance such that the authentication of genuine users can be smoothly accomplished. Second, the system should detect even subtle forgeries and reject possible intruders. The main contributions of this paper are as follows. First, we formally represent the underlying sketches by means of strings and present a general authentication algorithm that is based on structural pattern recognition. Second, we present a novel cost model that is particularly useful in conjunction with string matching. Third, by means of an exhaustive empirical investigation using both random and skilled forgeries (stemming from several hundreds of users) we empirically confirm the feasibility of this particular authentication framework in a real-world scenario.04 - Beitrag Sammelband oder Konferenzschrift
- PublikationOn the Relevance of Local Neighbourhoods for Greedy Graph Edit Distance(2016) Riesen, Kaspar; Robles-Kelly, Antonio [in: S+SSPR]04 - Beitrag Sammelband oder Konferenzschrift
- PublikationA Novel Graph Database for Handwritten Word Images(2016) Riesen, Kaspar; Robles-Kelly, Antonio [in: S+SSPR]04 - Beitrag Sammelband oder Konferenzschrift
- PublikationGraph-Based Keyword Spotting in Historical Handwritten Documents(2016) Riesen, Kaspar; Robles-Kelly, Antonio [in: S+SSPR]04 - Beitrag Sammelband oder Konferenzschrift
- PublikationLearning Heuristics to Reduce the Overestimation of Bipartite Graph Edit Distance Approximation(Springer, 2015) Ferrer, Miguel; Serratosa, Francesco; Riesen, Kaspar; Perner, Petra [in: Machine Learning and Data Mining in Pattern Recognition - 11th International Conference, MLDM 2015, Hamburg, Germany, July 20-21, 2015]In data mining systems, which operate on complex data with structural relationships, graphs are often used to represent the basic objects under study. Yet, the high representational power of graphs is also accompanied by an increased complexity of the associated algorithms. Exact graph similarity or distance, for instance, can be computed in exponential time only. Recently, an algorithmic framework that allows graph dissimilarity computation in cubic time with respect to the number of nodes has been presented. This fast computation is at the expense, however, of generally overestimating the true distance. The present paper introduces six different post-processing algorithms that can be integrated in this suboptimal graph distance framework. These novel extensions aim at improving the overall distance quality while keeping the low computation time of the approximation. An experimental evaluation clearly shows that the proposed heuristics substantially reduce the overestimation in the existing approximation framework while the computation time remains remarkably low.04 - Beitrag Sammelband oder Konferenzschrift
- PublikationImproving Approximate Graph Edit Distance by Means of a Greedy Swap Strategy(2014) Riesen, Kaspar; Bunke, Horst [in: 22nd International Conference on Pattern Recognition, ICPR 2014, Stockholm, Sweden, August 24-28, 2014]The authors of the present paper previously introduced a fast approximation framework for the graph edit distance problem. The basic idea of this approximation is to build a square cost matrix C = (c ij ), where each entry c ij reflects the cost of a node substitution, deletion or insertion plus the matching cost arising from the local edge structure. Based on C an optimal assignment of the nodes and their local structure is established in polynomial time. Yet, this procedure considers the graph structure only in a local way, and thus, an overestimation of the true graph edit distance has to be accepted. The present paper aims at reducing this overestimation by means of an additional greedy search strategy that builds upon the initial assignment. In an experimental evaluation on three real world data sets we empirically verify a substantial gain of distance accuracy while run time is nearly not affected.04 - Beitrag Sammelband oder Konferenzschrift
- PublikationClassification and Clustering of Vector Space Embedded Graphs(2011) Riesen, Kaspar; Bunke, Horst [in: Emerging Topics in Computer Vision and its Applications]04 - Beitrag Sammelband oder Konferenzschrift
- PublikationExact and Inexact Graph Matching: Methodology and Applications(Springer, 2010) Riesen, Kaspar; Jiang, Xiaoyi; Bunke, Horst [in: Managing and mining graph data]04 - Beitrag Sammelband oder Konferenzschrift
- PublikationOn Dissimilarity Embedding of Graphs in Vector Spaces(World Scientific, 2009) Bunke, Horst; Riesen, Kaspar [in: Handbook of Pattern Recognition and Computer Vision]04 - Beitrag Sammelband oder Konferenzschrift