15 Search Results for "Kr�ger, Stefan"


Document
Tight Algorithms for Connectivity Problems Parameterized by Clique-Width

Authors: Falko Hegerfeld and Stefan Kratsch

Published in: LIPIcs, Volume 274, 31st Annual European Symposium on Algorithms (ESA 2023)


Abstract
The complexity of problems involving global constraints is usually much more difficult to understand than the complexity of problems only involving local constraints. In the realm of graph problems, connectivity constraints are a natural form of global constraints. We study connectivity problems from a fine-grained parameterized perspective. In a breakthrough result, Cygan et al. (TALG 2022) first obtained Monte-Carlo algorithms with single-exponential running time α^{tw} n^𝒪(1) for connectivity problems parameterized by treewidth by introducing the cut-and-count-technique, which reduces many connectivity problems to locally checkable counting problems. Furthermore, the obtained bases α were shown to be optimal under the Strong Exponential-Time Hypothesis (SETH). However, since only sparse graphs may admit small treewidth, we lack knowledge of the fine-grained complexity of connectivity problems with respect to dense structure. The most popular graph parameter to measure dense structure is arguably clique-width, which intuitively measures how easily a graph can be constructed by repeatedly adding bicliques. Bergougnoux and Kanté (TCS 2019) have shown, using the rank-based approach, that also parameterized by clique-width many connectivity problems admit single-exponential algorithms. Unfortunately, the obtained running times are far from optimal under SETH. We show how to obtain optimal running times parameterized by clique-width for two benchmark connectivity problems, namely Connected Vertex Cover and Connected Dominating Set. These are the first tight results for connectivity problems with respect to clique-width and these results are obtained by developing new algorithms based on the cut-and-count-technique and novel lower bound constructions. Precisely, we show that there exist one-sided error Monte-Carlo algorithms that given a k-clique-expression solve - Connected Vertex Cover in time 6^k n^𝒪(1), and - Connected Dominating Set in time 5^k n^𝒪(1). Both results are shown to be tight under SETH.

Cite as

Falko Hegerfeld and Stefan Kratsch. Tight Algorithms for Connectivity Problems Parameterized by Clique-Width. In 31st Annual European Symposium on Algorithms (ESA 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 274, pp. 59:1-59:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)


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@InProceedings{hegerfeld_et_al:LIPIcs.ESA.2023.59,
  author =	{Hegerfeld, Falko and Kratsch, Stefan},
  title =	{{Tight Algorithms for Connectivity Problems Parameterized by Clique-Width}},
  booktitle =	{31st Annual European Symposium on Algorithms (ESA 2023)},
  pages =	{59:1--59:19},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-295-2},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{274},
  editor =	{G{\o}rtz, Inge Li and Farach-Colton, Martin and Puglisi, Simon J. and Herman, Grzegorz},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.ESA.2023.59},
  URN =		{urn:nbn:de:0030-drops-187124},
  doi =		{10.4230/LIPIcs.ESA.2023.59},
  annote =	{Keywords: Parameterized Complexity, Connectivity, Clique-width, Cut\&Count, Lower Bound}
}
Document
Towards Exact Structural Thresholds for Parameterized Complexity

Authors: Falko Hegerfeld and Stefan Kratsch

Published in: LIPIcs, Volume 249, 17th International Symposium on Parameterized and Exact Computation (IPEC 2022)


Abstract
Parameterized complexity seeks to optimally use input structure to obtain faster algorithms for NP-hard problems. This has been most successful for graphs of low treewidth, i.e., graphs decomposable by small separators: Many problems admit fast algorithms relative to treewidth and many of them are optimal under the Strong Exponential-Time Hypothesis (SETH). Fewer such results are known for more general structure such as low clique-width (decomposition by large and dense but structured separators) and more restrictive structure such as low deletion distance to some sparse graph class. Despite these successes, such results remain "islands" within the realm of possible structure. Rather than adding more islands, we seek to determine the transitions between them, that is, we aim for structural thresholds where the complexity increases as input structure becomes more general. Going from deletion distance to treewidth, is a single deletion set to a graph with simple components enough to yield the same lower bound as for treewidth or does it take many disjoint separators? Going from treewidth to clique-width, how much more density entails the same complexity as clique-width? Conversely, what is the most restrictive structure that yields the same lower bound? For treewidth, we obtain both refined and new lower bounds that apply already to graphs with a single separator X such that G-X has treewidth at most r = 𝒪(1), while G has treewidth |X|+𝒪(1). We rule out algorithms running in time 𝒪^*((r+1-ε)^k) for Deletion to r-Colorable parameterized by k = |X|; this implies the same lower bound relative to treedepth and (hence) also to treewidth. It specializes to 𝒪^*((3-ε)^k) for Odd Cycle Transversal where tw(G-X) ≤ r = 2 is best possible. For clique-width, an extended version of the above reduction rules out time 𝒪^*((4-ε)^k), where X is allowed to be a possibly large separator consisting of k (true) twinclasses, while the treewidth of G - X remains r; this is proved also for the more general Deletion to r-Colorable and it implies the same lower bound relative to clique-width. Further results complement what is known for Vertex Cover, Dominating Set and Maximum Cut. All lower bounds are matched by existing and newly designed algorithms.

Cite as

Falko Hegerfeld and Stefan Kratsch. Towards Exact Structural Thresholds for Parameterized Complexity. In 17th International Symposium on Parameterized and Exact Computation (IPEC 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 249, pp. 17:1-17:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)


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@InProceedings{hegerfeld_et_al:LIPIcs.IPEC.2022.17,
  author =	{Hegerfeld, Falko and Kratsch, Stefan},
  title =	{{Towards Exact Structural Thresholds for Parameterized Complexity}},
  booktitle =	{17th International Symposium on Parameterized and Exact Computation (IPEC 2022)},
  pages =	{17:1--17:20},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-260-0},
  ISSN =	{1868-8969},
  year =	{2022},
  volume =	{249},
  editor =	{Dell, Holger and Nederlof, Jesper},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.IPEC.2022.17},
  URN =		{urn:nbn:de:0030-drops-173734},
  doi =		{10.4230/LIPIcs.IPEC.2022.17},
  annote =	{Keywords: Parameterized complexity, lower bound, vertex cover, odd cycle transversal, SETH, modulator, treedepth, cliquewidth}
}
Document
Dealing with Variability in API Misuse Specification

Authors: Rodrigo Bonifácio, Stefan Krüger, Krishna Narasimhan, Eric Bodden, and Mira Mezini

Published in: LIPIcs, Volume 194, 35th European Conference on Object-Oriented Programming (ECOOP 2021)


Abstract
APIs are the primary mechanism for developers to gain access to externally defined services and tools. However, previous research has revealed API misuses that violate the contract of APIs to be prevalent. Such misuses can have harmful consequences, especially in the context of cryptographic libraries. Various API-misuse detectors have been proposed to address this issue - including CogniCrypt, one of the most versatile of such detectors and that uses a language (CrySL) to specify cryptographic API usage contracts. Nonetheless, existing approaches to detect API misuse had not been designed for systematic reuse, ignoring the fact that different versions of a library, different versions of a platform, and different recommendations/guidelines might introduce variability in the correct usage of an API. Yet, little is known about how such variability impacts the specification of the correct API usage. This paper investigates this question by analyzing the impact of various sources of variability on widely used Java cryptographic libraries (including JCA/JCE, Bouncy Castle, and Google Tink). The results of our investigation show that sources of variability like new versions of the API and security standards significantly impact the specifications. We then use the insights gained from our investigation to motivate an extension to the CrySL language (named MetaCrySL), which builds on meta-programming concepts. We evaluate MetaCrySL by specifying usage rules for a family of Android versions and illustrate that MetaCrySL can model all forms of variability we identified and drastically reduce the size of a family of specifications for the correct usage of cryptographic APIs.

Cite as

Rodrigo Bonifácio, Stefan Krüger, Krishna Narasimhan, Eric Bodden, and Mira Mezini. Dealing with Variability in API Misuse Specification. In 35th European Conference on Object-Oriented Programming (ECOOP 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 194, pp. 19:1-19:27, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)


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@InProceedings{bonifacio_et_al:LIPIcs.ECOOP.2021.19,
  author =	{Bonif\'{a}cio, Rodrigo and Kr\"{u}ger, Stefan and Narasimhan, Krishna and Bodden, Eric and Mezini, Mira},
  title =	{{Dealing with Variability in API Misuse Specification}},
  booktitle =	{35th European Conference on Object-Oriented Programming (ECOOP 2021)},
  pages =	{19:1--19:27},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-190-0},
  ISSN =	{1868-8969},
  year =	{2021},
  volume =	{194},
  editor =	{M{\o}ller, Anders and Sridharan, Manu},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.ECOOP.2021.19},
  URN =		{urn:nbn:de:0030-drops-140621},
  doi =		{10.4230/LIPIcs.ECOOP.2021.19},
  annote =	{Keywords: API misuse, cryptographic API misuse detection, code generation, domain engineering, cryptographic standards}
}
Document
Approximate Turing Kernelization for Problems Parameterized by Treewidth

Authors: Eva-Maria C. Hols, Stefan Kratsch, and Astrid Pieterse

Published in: LIPIcs, Volume 173, 28th Annual European Symposium on Algorithms (ESA 2020)


Abstract
We extend the notion of lossy kernelization, introduced by Lokshtanov et al. [STOC 2017], to approximate Turing kernelization. An α-approximate Turing kernel for a parameterized optimization problem is a polynomial-time algorithm that, when given access to an oracle that outputs c-approximate solutions in 𝒪(1) time, obtains an α ⋅ c-approximate solution to the considered problem, using calls to the oracle of size at most f(k) for some function f that only depends on the parameter. Using this definition, we show that Independent Set parameterized by treewidth 𝓁 has a (1+ε)-approximate Turing kernel with 𝒪(𝓁²/ε) vertices, answering an open question posed by Lokshtanov et al. [STOC 2017]. Furthermore, we give (1+ε)-approximate Turing kernels for the following graph problems parameterized by treewidth: Vertex Cover, Edge Clique Cover, Edge-Disjoint Triangle Packing and Connected Vertex Cover. We generalize the result for Independent Set and Vertex Cover, by showing that all graph problems that we will call friendly admit (1+ε)-approximate Turing kernels of polynomial size when parameterized by treewidth. We use this to obtain approximate Turing kernels for Vertex-Disjoint H-packing for connected graphs H, Clique Cover, Feedback Vertex Set and Edge Dominating Set.

Cite as

Eva-Maria C. Hols, Stefan Kratsch, and Astrid Pieterse. Approximate Turing Kernelization for Problems Parameterized by Treewidth. In 28th Annual European Symposium on Algorithms (ESA 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 173, pp. 60:1-60:23, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)


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@InProceedings{hols_et_al:LIPIcs.ESA.2020.60,
  author =	{Hols, Eva-Maria C. and Kratsch, Stefan and Pieterse, Astrid},
  title =	{{Approximate Turing Kernelization for Problems Parameterized by Treewidth}},
  booktitle =	{28th Annual European Symposium on Algorithms (ESA 2020)},
  pages =	{60:1--60:23},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-162-7},
  ISSN =	{1868-8969},
  year =	{2020},
  volume =	{173},
  editor =	{Grandoni, Fabrizio and Herman, Grzegorz and Sanders, Peter},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.ESA.2020.60},
  URN =		{urn:nbn:de:0030-drops-129261},
  doi =		{10.4230/LIPIcs.ESA.2020.60},
  annote =	{Keywords: Approximation, Turing kernelization, Graph problems, Treewidth}
}
Document
On Affine Reachability Problems

Authors: Stefan Jaax and Stefan Kiefer

Published in: LIPIcs, Volume 170, 45th International Symposium on Mathematical Foundations of Computer Science (MFCS 2020)


Abstract
We analyze affine reachability problems in dimensions 1 and 2. We show that the reachability problem for 1-register machines over the integers with affine updates is PSPACE-hard, hence PSPACE-complete, strengthening a result by Finkel et al. that required polynomial updates. Building on recent results on two-dimensional integer matrices, we prove NP-completeness of the mortality problem for 2-dimensional integer matrices with determinants +1 and 0. Motivated by tight connections with 1-dimensional affine reachability problems without control states, we also study the complexity of a number of reachability problems in finitely generated semigroups of 2-dimensional upper-triangular integer matrices.

Cite as

Stefan Jaax and Stefan Kiefer. On Affine Reachability Problems. In 45th International Symposium on Mathematical Foundations of Computer Science (MFCS 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 170, pp. 48:1-48:14, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)


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@InProceedings{jaax_et_al:LIPIcs.MFCS.2020.48,
  author =	{Jaax, Stefan and Kiefer, Stefan},
  title =	{{On Affine Reachability Problems}},
  booktitle =	{45th International Symposium on Mathematical Foundations of Computer Science (MFCS 2020)},
  pages =	{48:1--48:14},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-159-7},
  ISSN =	{1868-8969},
  year =	{2020},
  volume =	{170},
  editor =	{Esparza, Javier and Kr\'{a}l', Daniel},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.MFCS.2020.48},
  URN =		{urn:nbn:de:0030-drops-127148},
  doi =		{10.4230/LIPIcs.MFCS.2020.48},
  annote =	{Keywords: Counter Machines, Matrix Semigroups, Reachability}
}
Document
Compressing Permutation Groups into Grammars and Polytopes. A Graph Embedding Approach

Authors: Lars Jaffke, Mateus de Oliveira Oliveira, and Hans Raj Tiwary

Published in: LIPIcs, Volume 170, 45th International Symposium on Mathematical Foundations of Computer Science (MFCS 2020)


Abstract
It can be shown that each permutation group G ⊑ 𝕊_n can be embedded, in a well defined sense, in a connected graph with O(n+|G|) vertices. Some groups, however, require much fewer vertices. For instance, 𝕊_n itself can be embedded in the n-clique K_n, a connected graph with n vertices. In this work, we show that the minimum size of a context-free grammar generating a finite permutation group G⊑ 𝕊_n can be upper bounded by three structural parameters of connected graphs embedding G: the number of vertices, the treewidth, and the maximum degree. More precisely, we show that any permutation group G ⊑ 𝕊_n that can be embedded into a connected graph with m vertices, treewidth k, and maximum degree Δ, can also be generated by a context-free grammar of size 2^{O(kΔlogΔ)}⋅ m^{O(k)}. By combining our upper bound with a connection established by Pesant, Quimper, Rousseau and Sellmann [Gilles Pesant et al., 2009] between the extension complexity of a permutation group and the grammar complexity of a formal language, we also get that these permutation groups can be represented by polytopes of extension complexity 2^{O(kΔlogΔ)}⋅ m^{O(k)}. The above upper bounds can be used to provide trade-offs between the index of permutation groups, and the number of vertices, treewidth and maximum degree of connected graphs embedding these groups. In particular, by combining our main result with a celebrated 2^{Ω(n)} lower bound on the grammar complexity of the symmetric group 𝕊_n due to Glaister and Shallit [Glaister and Shallit, 1996] we have that connected graphs of treewidth o(n/log n) and maximum degree o(n/log n) embedding subgroups of 𝕊_n of index 2^{cn} for some small constant c must have n^{ω(1)} vertices. This lower bound can be improved to exponential on graphs of treewidth n^{ε} for ε < 1 and maximum degree o(n/log n).

Cite as

Lars Jaffke, Mateus de Oliveira Oliveira, and Hans Raj Tiwary. Compressing Permutation Groups into Grammars and Polytopes. A Graph Embedding Approach. In 45th International Symposium on Mathematical Foundations of Computer Science (MFCS 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 170, pp. 50:1-50:15, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)


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@InProceedings{jaffke_et_al:LIPIcs.MFCS.2020.50,
  author =	{Jaffke, Lars and de Oliveira Oliveira, Mateus and Tiwary, Hans Raj},
  title =	{{Compressing Permutation Groups into Grammars and Polytopes. A Graph Embedding Approach}},
  booktitle =	{45th International Symposium on Mathematical Foundations of Computer Science (MFCS 2020)},
  pages =	{50:1--50:15},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-159-7},
  ISSN =	{1868-8969},
  year =	{2020},
  volume =	{170},
  editor =	{Esparza, Javier and Kr\'{a}l', Daniel},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.MFCS.2020.50},
  URN =		{urn:nbn:de:0030-drops-127161},
  doi =		{10.4230/LIPIcs.MFCS.2020.50},
  annote =	{Keywords: Permutation Groups, Context Free Grammars, Extension Complexity, Graph Embedding Complexity}
}
Document
Elimination Distances, Blocking Sets, and Kernels for Vertex Cover

Authors: Eva-Maria C. Hols, Stefan Kratsch, and Astrid Pieterse

Published in: LIPIcs, Volume 154, 37th International Symposium on Theoretical Aspects of Computer Science (STACS 2020)


Abstract
The Vertex Cover problem plays an essential role in the study of polynomial kernelization in parameterized complexity, i.e., the study of provable and efficient preprocessing for NP-hard problems. Motivated by the great variety of positive and negative results for kernelization for Vertex Cover subject to different parameters and graph classes, we seek to unify and generalize them using so-called blocking sets. A blocking set is a set of vertices such that no optimal vertex cover contains all vertices in the blocking set, and the study of minimal blocking sets played implicit and explicit roles in many existing results. We show that in the most-studied setting, parameterized by the size of a deletion set to a specified graph class ?, bounded minimal blocking set size is necessary but not sufficient to get a polynomial kernelization. Under mild technical assumptions, bounded minimal blocking set size is showed to allow an essentially tight efficient reduction in the number of connected components. We then determine the exact maximum size of minimal blocking sets for graphs of bounded elimination distance to any hereditary class ?, including the case of graphs of bounded treedepth. We get similar but not tight bounds for certain non-hereditary classes ?, including the class ?_{LP} of graphs where integral and fractional vertex cover size coincide. These bounds allow us to derive polynomial kernels for Vertex Cover parameterized by the size of a deletion set to graphs of bounded elimination distance to, e.g., forest, bipartite, or ?_{LP} graphs.

Cite as

Eva-Maria C. Hols, Stefan Kratsch, and Astrid Pieterse. Elimination Distances, Blocking Sets, and Kernels for Vertex Cover. In 37th International Symposium on Theoretical Aspects of Computer Science (STACS 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 154, pp. 36:1-36:14, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)


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@InProceedings{hols_et_al:LIPIcs.STACS.2020.36,
  author =	{Hols, Eva-Maria C. and Kratsch, Stefan and Pieterse, Astrid},
  title =	{{Elimination Distances, Blocking Sets, and Kernels for Vertex Cover}},
  booktitle =	{37th International Symposium on Theoretical Aspects of Computer Science (STACS 2020)},
  pages =	{36:1--36:14},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-140-5},
  ISSN =	{1868-8969},
  year =	{2020},
  volume =	{154},
  editor =	{Paul, Christophe and Bl\"{a}ser, Markus},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.STACS.2020.36},
  URN =		{urn:nbn:de:0030-drops-118974},
  doi =		{10.4230/LIPIcs.STACS.2020.36},
  annote =	{Keywords: Vertex Cover, kernelization, blocking sets, elimination distance, structural parameters}
}
Document
On Kernelization for Edge Dominating Set under Structural Parameters

Authors: Eva-Maria C. Hols and Stefan Kratsch

Published in: LIPIcs, Volume 126, 36th International Symposium on Theoretical Aspects of Computer Science (STACS 2019)


Abstract
In the NP-hard Edge Dominating Set problem (EDS) we are given a graph G=(V,E) and an integer k, and need to determine whether there is a set F subseteq E of at most k edges that are incident with all (other) edges of G. It is known that this problem is fixed-parameter tractable and admits a polynomial kernelization when parameterized by k. A caveat for this parameter is that it needs to be large, i.e., at least equal to half the size of a maximum matching of G, for instances not to be trivially negative. Motivated by this, we study the existence of polynomial kernelizations for EDS when parameterized by structural parameters that may be much smaller than k. Unfortunately, at first glance this looks rather hopeless: Even when parameterized by the deletion distance to a disjoint union of paths P_3 of length two there is no polynomial kernelization (under standard assumptions), ruling out polynomial kernelizations for many smaller parameters like the feedback vertex set size. In contrast, somewhat surprisingly, there is a polynomial kernelization for deletion distance to a disjoint union of paths P_5 of length four. As our main result, we fully classify for all finite sets H of graphs, whether a kernel size polynomial in |X| is possible when given X such that each connected component of G-X is isomorphic to a graph in H.

Cite as

Eva-Maria C. Hols and Stefan Kratsch. On Kernelization for Edge Dominating Set under Structural Parameters. In 36th International Symposium on Theoretical Aspects of Computer Science (STACS 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 126, pp. 36:1-36:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)


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@InProceedings{hols_et_al:LIPIcs.STACS.2019.36,
  author =	{Hols, Eva-Maria C. and Kratsch, Stefan},
  title =	{{On Kernelization for Edge Dominating Set under Structural Parameters}},
  booktitle =	{36th International Symposium on Theoretical Aspects of Computer Science (STACS 2019)},
  pages =	{36:1--36:18},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-100-9},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{126},
  editor =	{Niedermeier, Rolf and Paul, Christophe},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.STACS.2019.36},
  URN =		{urn:nbn:de:0030-drops-102752},
  doi =		{10.4230/LIPIcs.STACS.2019.36},
  annote =	{Keywords: Edge dominating set, kernelization, structural parameters}
}
Document
CrySL: An Extensible Approach to Validating the Correct Usage of Cryptographic APIs

Authors: Stefan Krüger, Johannes Späth, Karim Ali, Eric Bodden, and Mira Mezini

Published in: LIPIcs, Volume 109, 32nd European Conference on Object-Oriented Programming (ECOOP 2018)


Abstract
Various studies have empirically shown that the majority of Java and Android apps misuse cryptographic libraries, causing devastating breaches of data security. It is crucial to detect such misuses early in the development process. To detect cryptography misuses, one must first define secure uses, a process mastered primarily by cryptography experts, and not by developers. In this paper, we present CrySL, a definition language for bridging the cognitive gap between cryptography experts and developers. CrySL enables cryptography experts to specify the secure usage of the cryptographic libraries that they provide. We have implemented a compiler that translates such CrySL specification into a context-sensitive and flow-sensitive demand-driven static analysis. The analysis then helps developers by automatically checking a given Java or Android app for compliance with the CrySL-encoded rules. We have designed an extensive CrySL rule set for the Java Cryptography Architecture (JCA), and empirically evaluated it by analyzing 10,000 current Android apps. Our results show that misuse of cryptographic APIs is still widespread, with 95% of apps containing at least one misuse. Our easily extensible CrySL rule set covers more violations than previous special-purpose tools with hard-coded rules, with our tooling offering a more precise analysis.

Cite as

Stefan Krüger, Johannes Späth, Karim Ali, Eric Bodden, and Mira Mezini. CrySL: An Extensible Approach to Validating the Correct Usage of Cryptographic APIs. In 32nd European Conference on Object-Oriented Programming (ECOOP 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 109, pp. 10:1-10:27, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)


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@InProceedings{kruger_et_al:LIPIcs.ECOOP.2018.10,
  author =	{Kr\"{u}ger, Stefan and Sp\"{a}th, Johannes and Ali, Karim and Bodden, Eric and Mezini, Mira},
  title =	{{CrySL: An Extensible Approach to Validating the Correct Usage of Cryptographic APIs}},
  booktitle =	{32nd European Conference on Object-Oriented Programming (ECOOP 2018)},
  pages =	{10:1--10:27},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-079-8},
  ISSN =	{1868-8969},
  year =	{2018},
  volume =	{109},
  editor =	{Millstein, Todd},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.ECOOP.2018.10},
  URN =		{urn:nbn:de:0030-drops-92151},
  doi =		{10.4230/LIPIcs.ECOOP.2018.10},
  annote =	{Keywords: cryptography, domain-specific language, static analysis}
}
Document
CrySL: An Extensible Approach to Validating the Correct Usage of Cryptographic APIs (Artifact)

Authors: Stefan Krüger, Johannes Späth, Karim Ali, Eric Bodden, and Mira Mezini

Published in: DARTS, Volume 4, Issue 3, Special Issue of the 32nd European Conference on Object-Oriented Programming (ECOOP 2018)


Abstract
In this artefact, we present CrySL, an extensible approach to validating the correct usage of cryptographic APIs. The artefact contains executables for CogniCrypt_{SAST}, the analysis CrySL-based analysis, along with the CrySL rules we used in in the original paper's experiments. We also provide scripts to re-run the experiments. We finally include a tutorial to showcase the CogniCrypt_{SAST} on a small Java target program.

Cite as

Stefan Krüger, Johannes Späth, Karim Ali, Eric Bodden, and Mira Mezini. CrySL: An Extensible Approach to Validating the Correct Usage of Cryptographic APIs (Artifact). In Special Issue of the 32nd European Conference on Object-Oriented Programming (ECOOP 2018). Dagstuhl Artifacts Series (DARTS), Volume 4, Issue 3, pp. 6:1-6:4, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)


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@Article{kruger_et_al:DARTS.4.3.6,
  author =	{Kr\"{u}ger, Stefan and Sp\"{a}th, Johannes and Ali, Karim and Bodden, Eric and Mezini, Mira},
  title =	{{CrySL: An Extensible Approach to Validating the Correct Usage of Cryptographic APIs (Artifact)}},
  pages =	{6:1--6:4},
  journal =	{Dagstuhl Artifacts Series},
  ISSN =	{2509-8195},
  year =	{2018},
  volume =	{4},
  number =	{3},
  editor =	{Kr\"{u}ger, Stefan and Sp\"{a}th, Johannes and Ali, Karim and Bodden, Eric and Mezini, Mira},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/DARTS.4.3.6},
  URN =		{urn:nbn:de:0030-drops-92371},
  doi =		{10.4230/DARTS.4.3.6},
  annote =	{Keywords: cryptography, domain-specific language, static analysis}
}
Document
Treasure Hunt with Barely Communicating Agents

Authors: Stefan Dobrev, Rastislav Královic, and Dana Pardubská

Published in: LIPIcs, Volume 95, 21st International Conference on Principles of Distributed Systems (OPODIS 2017)


Abstract
We consider the problem of fault-tolerant parallel exhaustive search, a.k.a. “Treasure Hunt”, introduced by Fraigniaud, Korman and Rodeh in [13]: Imagine an infinite list of “boxes”, one of which contains a “treasure”. The ordering of the boxes reflects the importance of finding the treasure in a given box. There are k agents, whose goal is to locate the treasure in the least amount of time. The system is synchronous; at every step, an agent can ”open” a box and see whether the treasure is there. The hunt finishes when the first agent locates the treasure. The original paper [13] considers non-cooperating randomized agents, out of which at most f can fail, with the failure pattern determined by an adversary. In this paper, we consider deterministic agents and investigate two failure models: The failing-agents model from [13] and a “black hole” model: At most f boxes contain “black holes”, placed by the adversary. When an agent opens a box containing a black hole, the agent disappears without an observable trace. The crucial distinction, however, is that we consider “barely communicating” or “indirectly weakly communicating” agents: When an agent opens a box, it can tell whether the box has been previously opened. There are no other means of direct or indirect communication between the agents. We show that adding even such weak means of communication has very strong impact on the solvability and complexity of the Treasure Hunt problem. In particular, in the failing agents model it allows the agents to be 1-competitive w.r.t. an optimal algorithm which does not know the location of the treasure, but is instantly notified of agent failures. In the black holes model (where there is no deterministic solution for non-communicating agents even in the presence of a single black hole) we show a lower bound of 2f + 1 and an upper bound of 4f + 1 for the number of agents needed to solve Treasure Hunt in presence of up to f black holes, as well as partial results about the hunt time in the presence of few black holes.

Cite as

Stefan Dobrev, Rastislav Královic, and Dana Pardubská. Treasure Hunt with Barely Communicating Agents. In 21st International Conference on Principles of Distributed Systems (OPODIS 2017). Leibniz International Proceedings in Informatics (LIPIcs), Volume 95, pp. 14:1-14:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)


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@InProceedings{dobrev_et_al:LIPIcs.OPODIS.2017.14,
  author =	{Dobrev, Stefan and Kr\'{a}lovic, Rastislav and Pardubsk\'{a}, Dana},
  title =	{{Treasure Hunt with Barely Communicating Agents}},
  booktitle =	{21st International Conference on Principles of Distributed Systems (OPODIS 2017)},
  pages =	{14:1--14:16},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-061-3},
  ISSN =	{1868-8969},
  year =	{2018},
  volume =	{95},
  editor =	{Aspnes, James and Bessani, Alysson and Felber, Pascal and Leit\~{a}o, Jo\~{a}o},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2017.14},
  URN =		{urn:nbn:de:0030-drops-86346},
  doi =		{10.4230/LIPIcs.OPODIS.2017.14},
  annote =	{Keywords: parallel exhaustive search, treasure hunt, fault-tolerant search, weak coordination, black holes}
}
Document
Generalizing Multi-Context Systems for Reactive Stream Reasoning Applications

Authors: Stefan Ellmauthaler

Published in: OASIcs, Volume 35, 2013 Imperial College Computing Student Workshop


Abstract
In the field of artificial intelligence (AI), the subdomain of knowledge representation (KR) has the aim to represent, integrate, and exchange knowledge in order to do some reasoning about the given information. During the last decades many different KR-languages were proposed for a variety of certain applications with specific needs. The concept of a managed Multi-Context System (mMCS) was introduced to provide adequate formal tools to interchange and integrate knowledge between different KR-approaches. Another arising field of interest in computer science is the design of online applications, which react directly to (possibly infinite) streams of information. This paper presents a genuine approach to generalize mMCS for online applications with continuous streams of information. Our major goal is to find a good tradeoff between expressiveness and computational complexity.

Cite as

Stefan Ellmauthaler. Generalizing Multi-Context Systems for Reactive Stream Reasoning Applications. In 2013 Imperial College Computing Student Workshop. Open Access Series in Informatics (OASIcs), Volume 35, pp. 19-26, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2013)


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@InProceedings{ellmauthaler:OASIcs.ICCSW.2013.19,
  author =	{Ellmauthaler, Stefan},
  title =	{{Generalizing Multi-Context Systems for Reactive Stream Reasoning Applications}},
  booktitle =	{2013 Imperial College Computing Student Workshop},
  pages =	{19--26},
  series =	{Open Access Series in Informatics (OASIcs)},
  ISBN =	{978-3-939897-63-7},
  ISSN =	{2190-6807},
  year =	{2013},
  volume =	{35},
  editor =	{Jones, Andrew V. and Ng, Nicholas},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/OASIcs.ICCSW.2013.19},
  URN =		{urn:nbn:de:0030-drops-42675},
  doi =		{10.4230/OASIcs.ICCSW.2013.19},
  annote =	{Keywords: Knowledge Representation, Artificial Intelligence}
}
Document
Geometric Distance Estimation for Sensor Networks and Unit Disk Graphs

Authors: Sándor Fekete, Alexander Kröller, Carsten Buschmann, and Stefan Fischer

Published in: Dagstuhl Seminar Proceedings, Volume 6481, Geometric Networks and Metric Space Embeddings (2007)


Abstract
We present an approach to estimating distances in sensor networks. It works by counting common neighbors, high values indicating closeness. Such distance estimates are needed in many self-localization algorithms. Other than many other approaches, ours does not rely on special equipment in the devices.

Cite as

Sándor Fekete, Alexander Kröller, Carsten Buschmann, and Stefan Fischer. Geometric Distance Estimation for Sensor Networks and Unit Disk Graphs. In Geometric Networks and Metric Space Embeddings. Dagstuhl Seminar Proceedings, Volume 6481, pp. 1-2, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2007)


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@InProceedings{fekete_et_al:DagSemProc.06481.2,
  author =	{Fekete, S\'{a}ndor and Kr\"{o}ller, Alexander and Buschmann, Carsten and Fischer, Stefan},
  title =	{{Geometric Distance Estimation for Sensor Networks and Unit Disk Graphs}},
  booktitle =	{Geometric Networks and Metric Space Embeddings},
  pages =	{1--2},
  series =	{Dagstuhl Seminar Proceedings (DagSemProc)},
  ISSN =	{1862-4405},
  year =	{2007},
  volume =	{6481},
  editor =	{Joachim Gudmundsson and Rolf Klein and Giri Narasimhan and Michiel Smid and Alexander Wolff},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/DagSemProc.06481.2},
  URN =		{urn:nbn:de:0030-drops-10282},
  doi =		{10.4230/DagSemProc.06481.2},
  annote =	{Keywords: Sensor networks, distance estimation, unit disk graphs.}
}
Document
Dagstuhl-Manifest zur Strategischen Bedeutung des Software Engineering in Deutschland

Authors: Manfred Broy, Matthias Jarke, Manfred Nagl, Hans Dieter Rombach, Armin B. Cremers, Jürgen Ebert, Sabine Glesner, Martin Glinz, Michael Goedicke, Gerhard Goos, Volker Gruhn, Wilhelm Hasselbring, Stefan Jähnichen, Stefan Kowalewski, Bernd J. Krämer, Stefan Leue, Claus Lewerentz, Peter Liggesmeyer, Christoph Lüth, Barbara Paech, Helmut A. Partsch, Ilka Philippow, Lutz Prechelt, Andreas Rausch, Willem-Paul de Roever, Bernhard Rumpe, Gudula Rünger, Wilhelm Schäfer, Kurt Schneider, Andy Schürr, Walter F. Tichy, Bernhard Westfechtel, Wolf Zimmermann, and Albert Zündorf

Published in: Dagstuhl Seminar Proceedings, Volume 5402, Perspectives Workshop (2006)


Abstract
Im Rahmen des Dagstuhl Perspektiven Workshop 05402 "Challenges for Software Engineering Research" haben führende Software Engineering Professoren den derzeitigen Stand der Softwaretechnik in Deutschland charakterisiert und Handlungsempfehlungen für Wirtschaft, Forschung und Politik abgeleitet. Das Manifest fasst die diese Empfehlungen und die Bedeutung und Entwicklung des Fachgebiets prägnant zusammen.

Cite as

Manfred Broy, Matthias Jarke, Manfred Nagl, Hans Dieter Rombach, Armin B. Cremers, Jürgen Ebert, Sabine Glesner, Martin Glinz, Michael Goedicke, Gerhard Goos, Volker Gruhn, Wilhelm Hasselbring, Stefan Jähnichen, Stefan Kowalewski, Bernd J. Krämer, Stefan Leue, Claus Lewerentz, Peter Liggesmeyer, Christoph Lüth, Barbara Paech, Helmut A. Partsch, Ilka Philippow, Lutz Prechelt, Andreas Rausch, Willem-Paul de Roever, Bernhard Rumpe, Gudula Rünger, Wilhelm Schäfer, Kurt Schneider, Andy Schürr, Walter F. Tichy, Bernhard Westfechtel, Wolf Zimmermann, and Albert Zündorf. Dagstuhl-Manifest zur Strategischen Bedeutung des Software Engineering in Deutschland. In Perspectives Workshop. Dagstuhl Seminar Proceedings, Volume 5402, pp. 1-16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2006)


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@InProceedings{broy_et_al:DagSemProc.05402.1,
  author =	{Broy, Manfred and Jarke, Matthias and Nagl, Manfred and Rombach, Hans Dieter and Cremers, Armin B. and Ebert, J\"{u}rgen and Glesner, Sabine and Glinz, Martin and Goedicke, Michael and Goos, Gerhard and Gruhn, Volker and Hasselbring, Wilhelm and J\"{a}hnichen, Stefan and Kowalewski, Stefan and Kr\"{a}mer, Bernd J. and Leue, Stefan and Lewerentz, Claus and Liggesmeyer, Peter and L\"{u}th, Christoph and Paech, Barbara and Partsch, Helmut A. and Philippow, Ilka and Prechelt, Lutz and Rausch, Andreas and de Roever, Willem-Paul and Rumpe, Bernhard and R\"{u}nger, Gudula and Sch\"{a}fer, Wilhelm and Schneider, Kurt and Sch\"{u}rr, Andy and Tichy, Walter F. and Westfechtel, Bernhard and Zimmermann, Wolf and Z\"{u}ndorf, Albert},
  title =	{{Dagstuhl-Manifest zur Strategischen Bedeutung des Software Engineering in Deutschland}},
  booktitle =	{Perspectives Workshop},
  pages =	{1--16},
  series =	{Dagstuhl Seminar Proceedings (DagSemProc)},
  ISSN =	{1862-4405},
  year =	{2006},
  volume =	{5402},
  editor =	{Manfred Broy and Manfred Nagl and Hans Dieter Rombach and Matthias Jarke},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/DagSemProc.05402.1},
  URN =		{urn:nbn:de:0030-drops-5853},
  doi =		{10.4230/DagSemProc.05402.1},
  annote =	{Keywords: Software Engineering, Software Technik, Strategie}
}
Document
Deterministic boundary recongnition and topology extraction for large sensor networks

Authors: Sándor Fekete, Alexander Kröller, Dennis Pfisterer, and Stefan Fischer

Published in: Dagstuhl Seminar Proceedings, Volume 5361, Algorithmic Aspects of Large and Complex Networks (2006)


Abstract
We present a new framework for the crucial challenge of self-organization of a large sensor network. The basic scenario can be described as follows: Given a large swarm of immobile sensor nodes that have been scattered in a polygonal region, such as a street network. Nodes have no knowledge of size or shape of the environment or the position of other nodes. Moreover, they have no way of measuring coordinates, geometric distances to other nodes, or their direction. Their only way of interacting with other nodes is to send or to receive messages from any node that is within communication range. The objective is to develop algorithms and protocols that allow self-organization of the swarm into large-scale structures that reflect the structure of the street network, setting the stage for global routing, tracking and guiding algorithms. Our algorithms work in two stages: boundary recognition and topology extraction. All steps are strictly deterministic, yield fast distributed algorithms, and make no assumption on the distribution of nodes in the environment, other than sufficient density.

Cite as

Sándor Fekete, Alexander Kröller, Dennis Pfisterer, and Stefan Fischer. Deterministic boundary recongnition and topology extraction for large sensor networks. In Algorithmic Aspects of Large and Complex Networks. Dagstuhl Seminar Proceedings, Volume 5361, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2006)


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@InProceedings{fekete_et_al:DagSemProc.05361.6,
  author =	{Fekete, S\'{a}ndor and Kr\"{o}ller, Alexander and Pfisterer, Dennis and Fischer, Stefan},
  title =	{{Deterministic boundary recongnition and topology extraction for large sensor networks}},
  booktitle =	{Algorithmic Aspects of Large and Complex Networks},
  series =	{Dagstuhl Seminar Proceedings (DagSemProc)},
  ISSN =	{1862-4405},
  year =	{2006},
  volume =	{5361},
  editor =	{Stefano Leonardi and Friedhelm Meyer auf der Heide and Dorothea Wagner},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/DagSemProc.05361.6},
  URN =		{urn:nbn:de:0030-drops-5632},
  doi =		{10.4230/DagSemProc.05361.6},
  annote =	{Keywords: Distributed algorithms, sensor networks, boundary recognition, topology extraction}
}
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