No abstract

The attack on RSA [12] in early 2011 represented a big surprise for the IT security industry. It showed that major security companies are attractive targets for stealthy attacks because of the important information they possess. The RSA attack induced an interesting discussion in the security industry and the research community alike. In particular, researchers at RSA modeled stealthy takeovers of a resource in their FlipIt game [13]. FlipIt is an attacker-defender game in which the players compete for the control of a resource, which can correspond to the practical case of updating and compromising a cryptographic key.In this paper, we present FlipThem, a generalization of the FlipIt game to multiple resources. In particular, we consider two control models: In the AND control model, the attacker needs to compromise all resources to gain access to the target system, whereas in the OR control model, the attacker only needs to control a single resource to reach her goal. First, we propose combinations of basic, single-resource FlipIt strategies and study the best choices for the defender and the attacker. Then, we extend these basic strategies with the Markov strategy class to represent more complex combinations of moves.Based on our FlipThem model, we can provide a few guidelines for the defenders. First, in the AND control model, we found that the defender should update her resources independently. On the other hand, the defender should generally update her resources synchronously in the OR control model. We also found that periodically updating resources is a good choice against a non-adaptive attacker in the FlipThem model, however, it suffers from the same weaknesses against an attacker with feedback as in the basic FlipIt model. Thus, the defender needs to carefully assess the potential information available to the attacker when choosing her strategy. In summary, our results enable a defender to plan her defense strategy against a range of attacker strategies.

Abstract. It is proved that the equation solvability problem can be solved in polynomial time for nite nilpotent rings. Ramsey's theorem is employed in the proof. Then, using the same technique, a theorem of Goldmann and Russell is reproved: the equation solvability problem can be solved in polynomial time for nite nilpotent groups.

No abstract

Abstract. We analyze the computational complexity of solving a single equation and checking identities over finite meta-abelian groups. Among others we answer a question of Goldmann and Russel from '98: We prove that it is decidable in polynomial time whether or not an equation over the six element group S 3 has a solution.

Abstract. Phase-type (PH) distributions are being used to model a wide range of phenomena in performance and dependability evaluation. The resulting models may be employed in analytical as well as in simulationdriven approaches. Simulations require the efficient generation of random variates from PH distributions. PH distributions have different representations and different associated computational costs for random-variate generation. In this paper we study the problem of efficient representation and efficient generation of PH distributed variates.

BuTools 2 is collection of computational methods that are useful for Markovian and non-Markovian matrix analytic performance analysis. It consists of various packages. There are packages to obtain, analyze, transform and minimize discrete and continuous time phase-type (PH) distributions and Markovian arrival processes (MAP); to fit empirical measurement data and to evaluate the result; to solve many performance measures of various Markovian queueing systems; and to solve block-structured Markov chains. All three major mathematical frameworks are supported: BuTools is released for MATLAB, Mathematica and NumPy/IPython as well, with the same features, with the same call interfaces. Every function is documented, the documentation is supplemented by many examples and the related citations. BuTools uses the state-of-the art algorithms and apart of the basic functionalities it contains several unique, difficult to implement procedures as well. of contributors include: Levente Bodrog, Peter Buchholz, Armin Heindl, András Horváth, István Kolossváry, András ACM ISBN 978-1-4503-2138-9.

The equivalence problem for a group G is the problem of deciding which equations hold in G. It is known that for finite nilpotent groups and certain other solvable groups, the equivalence problem has polynomial-time complexity. We prove that the equivalence problem for a finite nonsolvable group G is co-NP-complete by reducing the k-coloring problem for graphs to the equivalence problem, where k is the cardinality of G.