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24 pages, 2294 KiB  
Article
Fast Algorithm for Cyber-Attack Estimation and Attack Path Extraction Using Attack Graphs with AND/OR Nodes
by Eugene Levner and Dmitry Tsadikovich
Algorithms 2024, 17(11), 504; https://doi.org/10.3390/a17110504 - 4 Nov 2024
Viewed by 1108
Abstract
This paper studies the security issues for cyber–physical systems, aimed at countering potential malicious cyber-attacks. The main focus is on solving the problem of extracting the most vulnerable attack path in a known attack graph, where an attack path is a sequence of [...] Read more.
This paper studies the security issues for cyber–physical systems, aimed at countering potential malicious cyber-attacks. The main focus is on solving the problem of extracting the most vulnerable attack path in a known attack graph, where an attack path is a sequence of steps that an attacker can take to compromise the underlying network. Determining an attacker’s possible attack path is critical to cyber defenders as it helps identify threats, harden the network, and thwart attacker’s intentions. We formulate this problem as a path-finding optimization problem with logical constraints represented by AND and OR nodes. We propose a new Dijkstra-type algorithm that combines elements from Dijkstra’s shortest path algorithm and the critical path method. Although the path extraction problem is generally NP-hard, for the studied special case, the proposed algorithm determines the optimal attack path in polynomial time, O(nm), where n is the number of nodes and m is the number of edges in the attack graph. To our knowledge this is the first exact polynomial algorithm that can solve the path extraction problem for different attack graphs, both cycle-containing and cycle-free. Computational experiments with real and synthetic data have shown that the proposed algorithm consistently and quickly finds optimal solutions to the problem. Full article
(This article belongs to the Section Algorithms for Multidisciplinary Applications)
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Figure 1

Figure 1
<p>The flow chart of the proposed algorithm.</p>
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<p>(<b>a</b>) Example 1 adapted from [<a href="#B41-algorithms-17-00504" class="html-bibr">41</a>]. (<b>b</b>) Extracted minimum-length attack path.</p>
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<p>(<b>a</b>) Acyclic attack graph equipped with the node times. (<b>b</b>) Extracted minimum-length attack path for Example 2.</p>
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<p>(<b>a</b>) Attack graph with cycles. (<b>b</b>) Extracted minimum-length attack path.</p>
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<p>(<b>a</b>) The unweighted attack graph with cycles. (<b>b</b>) Extracted minimum-length attack path.</p>
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<p>Attack graph with cycles without an attack path.</p>
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<p>The extended attack graph with the start node (adapted from [<a href="#B20-algorithms-17-00504" class="html-bibr">20</a>]).</p>
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<p>Extracted minimum-length attack path for the attack graph in <a href="#algorithms-17-00504-f007" class="html-fig">Figure 7</a>.</p>
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<p>A scheme of defenders’ response to a malicious attack.</p>
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19 pages, 501 KiB  
Article
Ad-Hoc Lanzhou Index
by Akbar Ali, Yilun Shang, Darko Dimitrov and Tamás Réti
Mathematics 2023, 11(20), 4256; https://doi.org/10.3390/math11204256 - 11 Oct 2023
Cited by 2 | Viewed by 1244
Abstract
This paper initiates the study of the mathematical aspects of the ad-hoc Lanzhou index. If G is a graph with the vertex set {x1,,xn}, then the ad-hoc Lanzhou index of G is defined by [...] Read more.
This paper initiates the study of the mathematical aspects of the ad-hoc Lanzhou index. If G is a graph with the vertex set {x1,,xn}, then the ad-hoc Lanzhou index of G is defined by Lz˜(G)=i=1ndi(n1di)2, where di represents the degree of the vertex xi. Several identities for the ad-hoc Lanzhou index, involving some existing topological indices, are established. The problems of finding graphs with the extremum values of the ad-hoc Lanzhou index from the following sets of graphs are also attacked: (i) the set of all connected ξ-cyclic graphs of a fixed order, (ii) the set of all connected molecular ξ-cyclic graphs of a fixed order, (iii) the set of all graphs of a fixed order, and (iv) the set of all connected molecular graphs of a fixed order. Full article
Show Figures

Figure 1

Figure 1
<p>The structure of the graph <span class="html-italic">G</span> used in Lemma 3.</p>
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<p>The graphs possessing the lowest value of <math display="inline"><semantics> <mover accent="true"> <mrow> <mi>L</mi> <mi>z</mi> </mrow> <mo>˜</mo> </mover> </semantics></math> in the set of all <span class="html-italic">n</span>-order connected unicyclic graphs, for <math display="inline"><semantics> <mrow> <mi>n</mi> <mo>=</mo> <mn>5</mn> <mo>,</mo> <mn>6</mn> <mo>,</mo> <mn>7</mn> </mrow> </semantics></math>.</p>
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<p>The <span class="html-italic">n</span>-order bicyclic graph <math display="inline"><semantics> <mrow> <msubsup> <mi>B</mi> <mi>n</mi> <mrow> <mo>(</mo> <mn>1</mn> <mo>)</mo> </mrow> </msubsup> <mrow> <mo>(</mo> <msub> <mi>η</mi> <mn>1</mn> </msub> <mo>,</mo> <msub> <mi>η</mi> <mn>2</mn> </msub> <mo>,</mo> <msub> <mi>η</mi> <mn>3</mn> </msub> <mo>,</mo> <msub> <mi>η</mi> <mn>4</mn> </msub> <mo>)</mo> </mrow> </mrow> </semantics></math>, where <math display="inline"><semantics> <mrow> <msub> <mi>η</mi> <mn>1</mn> </msub> <mo>+</mo> <msub> <mi>η</mi> <mn>2</mn> </msub> <mo>+</mo> <msub> <mi>η</mi> <mn>3</mn> </msub> <mo>+</mo> <msub> <mi>η</mi> <mn>4</mn> </msub> <mo>=</mo> <mi>n</mi> <mo>−</mo> <mn>4</mn> <mo>≥</mo> <mn>1</mn> </mrow> </semantics></math> with <math display="inline"><semantics> <mrow> <msub> <mi>η</mi> <mn>1</mn> </msub> <mo>≥</mo> <msub> <mi>η</mi> <mn>4</mn> </msub> <mo>≥</mo> <mn>0</mn> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <msub> <mi>η</mi> <mn>2</mn> </msub> <mo>≥</mo> <msub> <mi>η</mi> <mn>3</mn> </msub> <mo>≥</mo> <mn>0</mn> </mrow> </semantics></math>.</p>
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<p>The <span class="html-italic">n</span>-order bicyclic graph <math display="inline"><semantics> <mrow> <msubsup> <mi>B</mi> <mi>n</mi> <mrow> <mo>(</mo> <mn>2</mn> <mo>)</mo> </mrow> </msubsup> <mrow> <mo>(</mo> <msub> <mi>η</mi> <mn>1</mn> </msub> <mo>,</mo> <msub> <mi>η</mi> <mn>2</mn> </msub> <mo>,</mo> <msub> <mi>η</mi> <mn>3</mn> </msub> <mo>,</mo> <msub> <mi>η</mi> <mn>4</mn> </msub> <mo>,</mo> <msub> <mi>η</mi> <mn>5</mn> </msub> <mo>)</mo> </mrow> </mrow> </semantics></math>, where <math display="inline"><semantics> <mrow> <msub> <mi>η</mi> <mn>1</mn> </msub> <mo>+</mo> <msub> <mi>η</mi> <mn>2</mn> </msub> <mo>+</mo> <msub> <mi>η</mi> <mn>3</mn> </msub> <mo>+</mo> <msub> <mi>η</mi> <mn>4</mn> </msub> <mo>+</mo> <msub> <mi>η</mi> <mn>5</mn> </msub> <mo>=</mo> <mi>n</mi> <mo>−</mo> <mn>5</mn> <mo>≥</mo> <mn>0</mn> </mrow> </semantics></math> with <math display="inline"><semantics> <mrow> <msub> <mi>η</mi> <mn>1</mn> </msub> <mo>≥</mo> <mo movablelimits="true" form="prefix">max</mo> <mrow> <mo>{</mo> <msub> <mi>η</mi> <mn>2</mn> </msub> <mo>,</mo> <msub> <mi>η</mi> <mn>3</mn> </msub> <mo>,</mo> <msub> <mi>η</mi> <mn>4</mn> </msub> <mo>}</mo> </mrow> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <msub> <mi>η</mi> <mi>i</mi> </msub> <mo>≥</mo> <mn>0</mn> </mrow> </semantics></math> for every <math display="inline"><semantics> <mrow> <mi>i</mi> <mo>∈</mo> <mo>{</mo> <mn>1</mn> <mo>,</mo> <mn>2</mn> <mo>,</mo> <mo>…</mo> <mo>,</mo> <mn>5</mn> <mo>}</mo> </mrow> </semantics></math>.</p>
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<p>The <span class="html-italic">n</span>-order bicyclic graphs <math display="inline"><semantics> <msub> <mi>B</mi> <mrow> <mi>n</mi> <mo>;</mo> <mi>α</mi> </mrow> </msub> </semantics></math> (on the left side) and <math display="inline"><semantics> <msubsup> <mi>B</mi> <mrow> <mi>n</mi> </mrow> <mo>*</mo> </msubsup> </semantics></math> (on the right side), where <math display="inline"><semantics> <mrow> <mn>0</mn> <mo>≤</mo> <mi>α</mi> <mo>≤</mo> <mo>⌊</mo> <mo>(</mo> <mi>n</mi> <mo>−</mo> <mn>4</mn> <mo>)</mo> <mo>/</mo> <mn>2</mn> <mo>⌋</mo> </mrow> </semantics></math>.</p>
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<p>The 6-order connected bicyclic graphs <math display="inline"><semantics> <msub> <mi>G</mi> <mn>1</mn> </msub> </semantics></math>, <math display="inline"><semantics> <msub> <mi>G</mi> <mn>2</mn> </msub> </semantics></math>, <math display="inline"><semantics> <msub> <mi>G</mi> <mn>3</mn> </msub> </semantics></math>, and <math display="inline"><semantics> <msub> <mi>G</mi> <mn>4</mn> </msub> </semantics></math>.</p>
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<p>The 7-order connected bicyclic graphs <math display="inline"><semantics> <mrow> <msub> <mi>H</mi> <mn>1</mn> </msub> <mo>,</mo> <msub> <mi>H</mi> <mn>2</mn> </msub> <mo>,</mo> <mo>…</mo> <mo>,</mo> <msub> <mi>H</mi> <mn>8</mn> </msub> </mrow> </semantics></math>.</p>
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<p>The graphs <math display="inline"><semantics> <mrow> <msub> <mi>J</mi> <mn>1</mn> </msub> <mo>,</mo> <msub> <mi>J</mi> <mn>2</mn> </msub> <mo>,</mo> <mo>…</mo> <mo>,</mo> <msub> <mi>J</mi> <mn>5</mn> </msub> <mo>,</mo> </mrow> </semantics></math> (from left to right, respectively) used in Theorem 6.</p>
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<p>All connected bicyclic graphs of order 5 and minimum degree at least 2, together with the values of <math display="inline"><semantics> <mover accent="true"> <mrow> <mi>L</mi> <mi>z</mi> </mrow> <mo>˜</mo> </mover> </semantics></math>.</p>
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<p>All connected tricyclic graphs of order 5 and minimum degree at least 2. The first, second, and third graphs (from left to right) have the following values of <math display="inline"><semantics> <mover accent="true"> <mrow> <mi>L</mi> <mi>z</mi> </mrow> <mo>˜</mo> </mover> </semantics></math>, respectively: 20, 22, and 24.</p>
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<p>The <span class="html-italic">n</span>-order connected tricyclic graphs <math display="inline"><semantics> <msup> <mi>G</mi> <mo>★</mo> </msup> </semantics></math> of maximum degree <math display="inline"><semantics> <mrow> <mi>n</mi> <mo>−</mo> <mn>1</mn> </mrow> </semantics></math> and minimum degree no less than 2, for <math display="inline"><semantics> <mrow> <mi>n</mi> <mo>=</mo> <mn>6</mn> <mo>,</mo> <mn>7</mn> </mrow> </semantics></math>.</p>
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