Results 1  10
of
28
Obstructionfree authorization enforcement: Aligning security with business objectives
 In Proc. of the IEEE Computer Security Foundations Symposium (CSF ’11
, 2011
"... Abstract—Access control is fundamental in protecting information systems but it also poses an obstacle to achieving business objectives. We analyze this tradeoff and its avoidance in the context of systems modeled as workflows restricted by authorization constraints including those specifying Separ ..."
Abstract

Cited by 6 (2 self)
 Add to MetaCart
Abstract—Access control is fundamental in protecting information systems but it also poses an obstacle to achieving business objectives. We analyze this tradeoff and its avoidance in the context of systems modeled as workflows restricted by authorization constraints including those specifying Separation of Duty (SoD) and Binding of Duty (BoD). To begin with, we present a novel approach to scoping authorization constraints within workflows with loops and conditional execution. Afterwards, we consider enforcement’s effects on business objectives. We identify the notion of obstruction, which generalizes deadlock within a system where access control is enforced, and we formulate the existence of an obstructionfree enforcement mechanism as a decision problem. We present lower and upper bounds for the complexity of this problem and also give an approximation algorithm that performs well when authorizations are equally distributed among users. To appear in:
Inapproximability of Rainbow Colouring
, 2013
"... A rainbow colouring of a connected graph G is a colouring of the edges of G such that every pair of vertices in G is connected by at least one path in which no two edges are coloured the same. The minimum number of colours required to rainbow colour G is called its rainbow connection number. Chakrab ..."
Abstract

Cited by 2 (0 self)
 Add to MetaCart
A rainbow colouring of a connected graph G is a colouring of the edges of G such that every pair of vertices in G is connected by at least one path in which no two edges are coloured the same. The minimum number of colours required to rainbow colour G is called its rainbow connection number. Chakraborty, Fischer, Matsliah and Yuster have shown that it is NPhard to compute the rainbow connection number of graphs [J. Comb. Optim., 2011]. Basavaraju, Chandran, Rajendraprasad and Ramaswamy have reported an (r + 3)factor approximation algorithm to rainbow colour any graph of radius r [Graphs and Combinatorics, 2012]. In this article, we use a result of Guruswami, Håstad and Sudan on the NPhardness of colouring a 2colourable 4uniform hypergraph using constantly many colours [SIAM J. Comput., 2002] to show that for every positive integer k, it is NPhard to distinguish between graphs with rainbow connection number 2k + 2 and 4k + 2. This, in turn, implies that there cannot exist a polynomial time algorithm to rainbow colour graphs with less than twice the optimum number of colours, unless P = NP. The authors have earlier shown that the rainbow connection number problem remains NPhard even when restricted to the class of chordal graphs, though in this case a 4factor approximation algorithm is available [COCOON, 2012]. In this article, we improve upon the 4factor approximation algorithm to design a lineartime algorithm that can rainbow colour a chordal graph G using at most 3/2 times the minimum number of colours if G is bridgeless and at most 5/2 times the minimum number of colours otherwise. Finally we show that the rainbow connection number of bridgeless chordal graphs cannot be polynomialtime approximated to a factor less than 5/4, unless P = NP.
BContinuity in Peterson graph and power of a Cycle
, 2012
"... A graph G is kcolorable if G has a proper vertex coloring with k colors. The chromatic number �(G) is the minimum number k such that G is kcolorable. A bcoloring of a graph with k colors is a proper coloring in which each color class contains a color dominating vertex. The largest positive integ ..."
Abstract

Cited by 1 (1 self)
 Add to MetaCart
A graph G is kcolorable if G has a proper vertex coloring with k colors. The chromatic number �(G) is the minimum number k such that G is kcolorable. A bcoloring of a graph with k colors is a proper coloring in which each color class contains a color dominating vertex. The largest positive integer k for which G has a bcoloring with k colors is the bchromatic number of G, denoted by b(G). The bspectrum Sb(G) of G, is defined as the set of all integers k at which G is bcolorable with k colors. A graph G is bcontinuous if its bspectrum equals [�(G), b(G)]. In this paper, we prove that the Peterson graph and the power of a cycle are bcontinuous. Also, we prove that the Cartesian product of two cycles Cm�Cn is bcontinuous when m and n are multiples of 5. In this case, we give the color classes of bcoloring with k colors for each k with �(G) � k � b(G).
Geometric achromatic and pseudoachromatic indices
, 2015
"... The pseudoachromatic index of a graph is the maximum number of colors that can be assigned to its edges, such that each pair of different colors is incident to a common vertex. If for each vertex its incident edges have different color, then this maximum is known as achromatic index. Both indices h ..."
Abstract

Cited by 1 (0 self)
 Add to MetaCart
The pseudoachromatic index of a graph is the maximum number of colors that can be assigned to its edges, such that each pair of different colors is incident to a common vertex. If for each vertex its incident edges have different color, then this maximum is known as achromatic index. Both indices have been widely studied. A geometric graph is a graph drawn in the plane such that its vertices are points in general position, and its edges are straightline segments. In this paper we extend the notion of pseudoachromatic and achromatic indices for geometric graphs, and present results for complete geometric graphs. In particular, we show that for n points in convex position the achromatic index and the pseudoachromatic index of the complete geometric graph are bn2+n 4 c.