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  <front>
    <journal-meta />
    <article-meta>
      <title-group>
        <article-title>Functional dependency graphs for cyber risk assessment in 5G-enabled ICS/OT networks</article-title>
      </title-group>
      <contrib-group>
        <contrib contrib-type="author">
          <string-name>Alla Pinchuk</string-name>
          <email>alla.pinchuk@kai.edu.ua</email>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Roman Odarchenko</string-name>
          <email>roman.odarchenko@npp.kai.edu.ua</email>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Oleh Poliheko</string-name>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Oleksandr Dobrynchuk</string-name>
          <email>oleksandr.dobrynchuk@npp.kai.edu.ua</email>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Vladyslav Pevnev</string-name>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <aff id="aff0">
          <label>0</label>
          <institution>State University "Kyiv Aviation Institute"</institution>
          ,
          <addr-line>Liubomyra Huzara Ave., 1, Kyiv, 03058</addr-line>
          ,
          <country country="UA">Ukraine</country>
        </aff>
      </contrib-group>
      <abstract>
        <p>The convergence of Industrial Control Systems (ICS) and Operational Technologies (OT) with 5G networks introduces complex cyber-physical infrastructures with dynamic topologies, high interconnectivity, and missioncritical latency requirements. Traditional risk assessment methods are inadequate in this situation because they do not consider the possibility of cascading failures among closely related system components. This paper proposes a cyber risk assessment approach based on functional dependency graphs, which model interdependencies among assets, processes, and communication flows in ICS/OT environments enabled by 5G. The suggested framework supports impact scoring based on graph-theoretic metrics, vulnerability propagation modeling, dependency graph construction, and passive and active data collection.</p>
      </abstract>
      <kwd-group>
        <kwd>eol&gt;ICS/OT network security</kwd>
        <kwd>functional dependency graph</kwd>
        <kwd>5G environment</kwd>
        <kwd>cybersecurity risk assessment</kwd>
      </kwd-group>
    </article-meta>
  </front>
  <body>
    <sec id="sec-1">
      <title>1. Introduction</title>
      <p>The integration of fifth-generation (5G) technologies into industrial control systems (ICS) and operational
technology (OT) environments is facilitating the transition to digitalization, automation, and the
implementation of Industry 4.0 concepts. The main advantages of using 5G in industrial systems are
support for high connection density (mMTC), ultra-reliable and low latency communication (URLLC),
and extended bandwidth (eMBB).</p>
      <p>However, the combination of ICS/OT and 5G brings new cybersecurity challenges. Unlike traditional
isolated ICS/OT networks, modern hybrid architectures are characterized by a high degree of component
interdependence, dynamically changing topology, and virtualization of network functions. This expands
the attack surface and complicates the identification of vulnerabilities, especially those that can cause
cascading failures.</p>
      <p>Most modern vulnerability assessment solutions are focused on analyzing individual assets and
do not take into account the functional dependency between ICS/OT components and 5G network
elements. This approach does not allow for the full identification of ways of cybersecurity threats
spreading and assessing the risks arising from the structural interdependence of systems.</p>
      <p>This paper proposes the development of a functional dependency graph module for a vulnerability
scanning system in ICS/OT 5G-enabled networks. The proposed approach allows for the dynamic
modeling of the dependencies between assets, assessing cascading risks, and prioritizing identified
vulnerabilities based on the topological characteristics and criticality of infrastructure elements.</p>
    </sec>
    <sec id="sec-2">
      <title>2. Background analysis</title>
      <p>
        ICS and OT have long been designed as isolated, closed environments focusing on reliability rather
than security. Traditionally, security was provided by physical access restrictions and a stable network
topology [
        <xref ref-type="bibr" rid="ref1">1</xref>
        ]. However, modern digitalization trends, including the Industrial Internet of Things (IIoT),
cloud services, and edge computing, radically change the ICS/OT landscape, making it harder to control
and creating numerous attack vectors [
        <xref ref-type="bibr" rid="ref2">2</xref>
        ].
      </p>
      <p>
        With the growing role of IP connections and remote management, ICS/OT environments are
increasingly exposed to typical IT cybersecurity threats to which these systems were not originally adapted.
Paper [
        <xref ref-type="bibr" rid="ref3">3</xref>
        ] discusses the concept of SCADA control using 5G, emphasizing new types of interconnections
and isolation challenges.
      </p>
      <p>
        To mitigate risks, some studies focus on traditional protection methods, such as segmentation,
access restrictions, and software updates. For example, [
        <xref ref-type="bibr" rid="ref4">4</xref>
        ] proposes a systematic approach to reducing
cybersecurity risks in ICS through access policies, multi-level protection, and monitoring. However,
this approach still does not taking into account the specifics of the new 5G architecture.
      </p>
      <p>
        The network’s expansion by connecting many sensors and devices in the IIoT environment, combined
with 5G characteristics such as URLLC, MEC, and slicing, creates situations where classical risk
assessment approaches lose their efectiveness. In [
        <xref ref-type="bibr" rid="ref5">5</xref>
        ], the ACSRA ICS method is presented, an automated
risk assessment considering interaction between nodes. However, the implementation does not cover
slice-oriented access, massive device connectivity, or the logic of virtualized functions.
      </p>
      <p>
        A more in-depth analysis of 5G security in an industrial context is provided in [
        <xref ref-type="bibr" rid="ref6">6</xref>
        ], which explores
the challenges associated with interfaces between OT and virtualized 5G components. The authors
note the dificulty in detecting attacks directed through AMF, UPF, or SMF, especially in conditions of
limited monitoring.
      </p>
      <p>
        The topic of modeling OT network structures is also reflected in [
        <xref ref-type="bibr" rid="ref7">7</xref>
        ], which provides an overview of
tools for building OT topologies, analyzing nodes, and identifying potentially critical points. However,
the work lacks a formalized apparatus for modeling the dependencies between OT processes and 5G
functions.
      </p>
      <p>
        In [
        <xref ref-type="bibr" rid="ref8">8</xref>
        ], a method for automated testing of 5G network slices is considered, which allows detecting
vulnerabilities related to the logic of slice isolation and the orchestration of VNFs. Despite the detail
of the threat model, the study does not provide a mechanism for assessing the impact on physical OT
components.
      </p>
      <p>
        Practical aspects of 5G integration into critical infrastructure are analyzed in [
        <xref ref-type="bibr" rid="ref9">9</xref>
        ], which presents a
case study of building a secure 5G network to monitor facilities’ technical condition. The work shows
the efectiveness of the slice-based architecture, but there is no risk assessment taking into account
cascading efects between elements.
      </p>
      <p>
        A separate area concerns trafic analysis in heterogeneous networks. A neural model for recognizing
modulation types in 5G networks is presented in [
        <xref ref-type="bibr" rid="ref10">10</xref>
        ]. This approach can be helpful in passively
detecting anomalies in trafic, but does not provide an idea of the impact of one component on another
in the system logic.
      </p>
      <p>
        In [
        <xref ref-type="bibr" rid="ref11">11</xref>
        ], load balancing between parallel servers in distributed systems is finally considered. Although
not directly related to security, the concept can be adapted to simulate fault tolerance or loss of
functionality in ICS/OT environments in cascading-failure scenarios.
      </p>
      <p>Thus, although existing research covers certain aspects, such as slice security, trafic modeling,
or access control, it does not address the key problem: the lack of a formalized model of functional
dependencies between OT elements and virtualized 5G components that would allow modeling the
propagation of risks in time and space. This creates the need to build a new apparatus for assessing
threats in such hybrid networks.</p>
    </sec>
    <sec id="sec-3">
      <title>3. Problem statement</title>
      <p>An analysis of scientific research has shown that despite the rapid growth of 5G integration into
ICS/OT environments, existing approaches to cybersecurity risk assessment remain largely fragmented.
Most available tools focus on identifying vulnerabilities of individual assets or use static risk models
that do not consider the specifics of 5G architecture. In particular, new risks arise from the complex
interaction of virtualized network functions (VNFs), massive connectivity of IIoT devices, the use of
MEC technologies, and slice-based access logic.</p>
      <p>The lack of formalized approaches that allow modeling functional dependencies between ICS/OT
processes, 5G network services, and virtual components is particularly critical. Such dependencies
determine how risks propagate in the system - in time, through interaction logic, or shared resources.
Without a model that considers these aspects, it is impossible to accurately assess the cascading impact,
criticality of nodes, and response priority.</p>
      <p>Thus, this research paper aims to develop a methodology for formalizing functional dependency
graphs (FDGs) for use in quantifying cyber risks in hybrid 5G-enabled ICS/OT networks.</p>
      <p>To achieve this goal, the following research objectives should be solved:
1. To conduct an analysis of existing approaches to modeling risks and dependencies in ICS/OT
networks and 5G environments, identifying their limitations in terms of intercomponent interaction.
2. To define requirements for the functional dependency graph in the context of 5G-enabled ICS/OT,
including types of links, node categories, temporal properties, and asset criticality.
3. To develop a formal mathematical model of FDG that describes the functional relationships
between system elements and allows tracking risk transformation in dynamics.
4. To integrate the FDG into a risk assessment model that calculates system-level metrics, identifies
critical nodes and threat propagation trajectories, and prioritizes response measures.</p>
    </sec>
    <sec id="sec-4">
      <title>4. Existing approaches analysis</title>
      <p>Modern approaches to analyzing cybersecurity risks and interconnection dependencies in ICS/OT
networks and 5G environments have been developed in isolation, leading to the lack of comprehensive
solutions for hybrid architectures. This section systematizes the main research directions and identifies
their limitations in the context of structural interaction, timing characteristics, and cascading efects.</p>
      <sec id="sec-4-1">
        <title>4.1. ICS/OT environments</title>
        <p>
          In traditional ICS/OT systems, risk analysis is based on the following approaches:
• signature-based threat detection methods (e.g., Snort, Bro) adapted to industrial protocols (Modbus,
DNP3). They are efective for known attacks but do not consider functional dependencies between
process components [
          <xref ref-type="bibr" rid="ref12 ref13 ref14">12, 13, 14</xref>
          ];
• frameworks such as NIST SP 800-82 focus on developing security policies but do not contain
a formal apparatus for analyzing inter-node impacts or simulating the efect of incidents in
dynamics [
          <xref ref-type="bibr" rid="ref15 ref16 ref17">15, 16, 17</xref>
          ];
• attack graphs and trees allow for the description of compromise scenarios from an attacker’s
perspective [
          <xref ref-type="bibr" rid="ref18">18, 19</xref>
          ]. However, most of these models are static, do not cover the time evolution of
risk, and do not consider the logic of functional dependencies between devices;
• individual asset metrics based on CVSS or RPN that assess the criticality of nodes but ignore the
structural context of their interaction [20, 21].
        </p>
      </sec>
      <sec id="sec-4-2">
        <title>4.2. 5G-based systems</title>
        <p>In 5G networks, threats are associated with virtualized functions, APIs, dynamic slices, and MEC
applications. Existing approaches mainly focus on these aspects:</p>
        <p>• vulnerability analysis of APIs, orchestrators, and configurations in VNFs [ 22] allows for identifying
individual threats. Still, it does not allow assessing their impact on other components, particularly
in the OT layer;
• graph-based policy compliance frameworks that provide access control based on dependencies
between services [23], but do not cover physical infrastructure or industrial processes;
• assessment of slice isolation and cross-slice attack vectors [24], which demonstrates threats in
a virtual environment but does not analyze how changes in the 5G network afect critical OT
assets;
• ML/AI-based tools, such as GNN-based anomaly detection [25], can detect anomalies in trafic
but do not provide an interpretable model of functional dependencies between system nodes.</p>
      </sec>
      <sec id="sec-4-3">
        <title>4.3. Identified limitations</title>
        <p>The analysis allows us to identify several key limitations of existing approaches:
• lack of an integrated representation of the hybrid ICS/OT+5G environment;
• restrictions on the display of inter-node dependencies in the physical, logical, and service space;
• ignoring the time dynamics of impact propagation (activation time, delay, duration);
• inability to support cascading risk assessment that takes into account contextual interactions
between ICS/OT and VNFs;
• insuficient flexibility in graph structures adapted to slice, MEC, and IIoT dynamics [25, 26].</p>
        <p>Current approaches provide a local risk assessment or a limited representation of the interaction
logic between components. None of them allows for a formalized structure that can take into account:
multi-level topology, temporal attributes, and criticality of assets in connection with technological
management processes.</p>
        <p>This creates a justified need to develop a functional dependency graph (FDG) that would combine
the logic of interconnections, support impact propagation modeling, and form the basis of a systemic
risk assessment.</p>
      </sec>
    </sec>
    <sec id="sec-5">
      <title>5. Functional dependency graphs requirements</title>
      <p>The integration of 5G with ICS/OT creates a multi-level environment where components with diferent
natures (physical, virtual, mobile) interact through functional dependencies. In such an environment,
identifying and assessing cybersecurity risks requires an abstract but suficiently accurate representation
of the relationships between components. For this purpose, we propose a functional dependency graph
model that serves as a structural basis for further quantitative risk analysis. This section formalizes the
basic requirements for such a model at the architectural and semantic levels. The general approach for
this is shown in Figure 1.</p>
      <sec id="sec-5-1">
        <title>5.1. Graph nodes classification</title>
        <p>In the context of 5G-integrated ICS/OT networks, the FDG nodes are classified by their functional role
and origin, as shown in Figure 2.</p>
        <p>ICS/OT components cover the classic elements of process control systems, such as programmable
logic controllers (PLCs), human-machine interfaces (HMIs), sensors, SCADA servers, remote terminal
units (RTUs), etc. These nodes are directly connected to the physical process and often have limited
computing resources.</p>
        <p>5G infrastructure includes hardware and software components of the fifth-generation mobile network,
including base stations (gNB, CPE), network core functions (AMF, UPF, SMF), MEC servers with local
applications, as well as orchestrators and API gateways. They implement network virtualization, trafic
routing, and provide mobile connectivity for critical services.</p>
        <p>IIoT/Edge devices and services encompass endpoint intelligent devices (e.g., autonomous sensors,
industrial robots), as well as cloud-based analytics and visualization services. It also includes programs
and systems that interact with the network through slides and process data in real time.</p>
        <p>This classification serves as the basis for formalizing the FDG structure, allowing you to display all
relevant elements of the hybrid environment and set rules for building inter-node functional dependencies
in the subsequent mathematical model.</p>
      </sec>
      <sec id="sec-5-2">
        <title>5.2. Functional dependencies types</title>
        <p>In the structure of a functional dependency graph, edges serve to formalize internode interactions that
have functional, logical, or operational significance. The typology of edges determines the nature of
the dependency between the system components and allows you to display its dynamic properties.
Depending on the nature of the interaction, the following main types of functional links are distinguished,
as shown in Figure 3.</p>
        <p>Data Dependency occurs when one node (A) generates or transmits information that is critical to the
functioning of another node (B). Such a dependency is typical for sensor monitoring scenarios, when
data from the sensor is sent to the controller (Sensor → PLC), or process visualization (PLC → HMI).</p>
        <p>Control Dependency occurs when one component determines the logic, state, or activation of another.
For example, an MEC application can initiate an action by a device (MEC App → Actuator), or an SMF
network element can control flows through UPF (SMF → UPF). Such dependencies are critical for the
correct functioning of a distributed architecture.</p>
        <p>Resource Coupling is a resource or physical dependency that is related to the use of a shared
computing, network, or slice resource. In cases where several nodes use the same MEC server or UPF,
an indirect functional dependency (IIoT1 → MEC ← IIoT2) occurs, which can become a source of
cascading failures when a common resource is overloaded or attacked.</p>
        <p>Temporal Constraint displays the constraints imposed by temporal characteristics, such as delay,
refresh rate, and timeout duration. For example, the interaction between a sensor and a controller may
require a delivery guarantee within 10 ms. Violation of the time parameters can lead to degradation of
the control process or an emergency condition.</p>
        <p>Logical or service connectivity (Functional Linkage) defines situations where multiple nodes
implement the same logical or process flow. An example is components that are part of the same SCADA
lfow or process route, even if there is no direct data or command transfer between them.</p>
        <p>Each edge in the FDG is described by a set of semantic attributes, including:
• direction of interaction (unidirectional → or reciprocal ↔);
• type of dependency (data, control, resource, etc.);
• reaction time or permissible delay (in milliseconds);
• degree of functional impact (low, medium, high);
• the possibility of degradation (with the loss of part of the functionality)..</p>
      </sec>
      <sec id="sec-5-3">
        <title>5.3. Semantic attributes of nodes and links</title>
        <p>To enable quantitative analysis of cybersecurity risks in hybrid 5G-enabled ICS/OT environments, it
is necessary to supplement the functional dependency graph with a system of semantic attributes.
This metadata allows not only to identify the functional role of nodes and links, but also to assess the
potential impact of a breach, the level of criticality, and the sensitivity of the system to attacks.</p>
        <p>The main semantic attributes include:
• Criticality: defines the degree of importance of a node to ensure the continuity of a technological
or management process. The value can be assigned manually by an expert (e.g., based on HAZOP
or PHA procedures) or determined automatically by analyzing the role of the node in the SCADA
logic. Components with high criticality (e.g., a PLC or actuator in a safety chain) are prioritized
in the risk assessment.
• Trust Level: displays the level of trust in a component or source of interaction, which is key for
modeling threats in mixed security environments. A low trust level can be assigned to external
IIoT devices, third-party APIs, slice-tenants, or nodes with unknown security status. The attribute
is used when modeling penetration or lateral movement scenarios.
• Latency / Frequency: includes the communication parameters: maximum allowable latency and
refresh rate. For real-time nodes (e.g., HMI - actuator) or critical URLLC networks, these attributes
define the allowable window of influence within which an attack can lead to a technological
failure.
• Node Role: defines the primary purpose of a node in the information system, such as sensing,
processing, storage, communication, control, and actuation. This classification allows you to
analyze potential chains of influence, for example: sensor - processing - reaction.
• Redundancy / Failover: indicates the presence of an alternate route or redundant component. If a
node has redundancy (for example, a dual MEC server or multiple parallel sensors), its failure has
a lower risk priority. This attribute is taken into account when modeling system resilience.
• Impact Range: determines the scope or number of components that can be impacted if a node is
compromised. For example, a compromise of a slice manager can afect dozens of IIoT applications.</p>
        <p>This allows to assess the scale of cascading risk in a dynamic environment.</p>
      </sec>
      <sec id="sec-5-4">
        <title>5.4. Architectural requirements for FDG</title>
        <p>Designing a functional dependency graph for environments that integrate ICS/OT components with
5G infrastructure requires taking into account the multidimensional complexity of such integration.
Given the increasing interdependence of physical, virtualized, and mobile elements, the FDG model
must provide a formalized representation of relationships between components without losing semantic
accuracy. Thus, it is possible to identify the following basic requirements: heterogeneity, dynamism,
scalability, compatibility with data sources, and suitability for risk analysis.</p>
        <p>One of the basic requirements is to support heterogeneity. The graph should unifiedly cover both
physical objects (sensors, actuators, RTUs) and software-defined functions (VNFs, MEC services, cloud
controllers). It is important that the model allows for a scalable representation of diferences in
communication protocols, timing characteristics, and functional roles of nodes without reducing them
to simplified types.</p>
        <p>The next critical property is adaptability to network dynamics. The features of 5G infrastructures,
including device mobility, dynamic slice creation, and real-time routing changes, require FDG to be
able to incrementally update. For this purpose, the model must be integrated with telemetry sources,
CMDBs, and orchestrator event streams, allowing the dependency structure to be updated without
manual intervention.</p>
        <p>Since real-world industrial deployments involve tens or hundreds of thousands of interconnected
nodes, scalability is a must. The graph must support processing large amounts of data without
performance degradation, using optimized data structures and the ability to compute on subgraphs with
parallel processing.</p>
        <p>It is also important to ensure interoperability with security and management systems. The FDG
should have built-in mechanisms for interacting with SCADA, SIEM, CMDB, vulnerability scanners,
and other tools that can automatically provide both structural and semantic information about system
components. This will avoid manual filling of the graph and ensure its compliance with the actual state
of the environment.</p>
        <p>Moreover, the graph structure should be analytically suitable for risk assessment. This includes
support for simulating the spread of threats, identifying critical nodes, analyzing chains of influence,
and prioritizing response scenarios. The graph should serve not only as a visualization tool, but also as
a basis for formalized scenario analysis that takes into account time constraints, the level of criticality
of assets, and trust in sources of influence.</p>
        <p>The formed model of the FDG functional dependency graph allows us to represent the structure
of a hybrid ICS/OT-5G system as a set of links enriched with semantics and criticality. This creates
the basis for further mathematical formalization and construction of the risk assessment model in the
following sections. The approach allows to take into account the specifics of inter-network interaction,
time dependence and dynamics of modern industrial environments.</p>
      </sec>
      <sec id="sec-5-5">
        <title>5.5. Formalization of a mathematical model of a functional dependency graph</title>
        <p>In order to formalize the representation of interconnections in hybrid ICS/OT environments with
integrated 5G infrastructure, it is proposed to use an oriented annotated dependency graph. Such a
structure allows not only to display the functional topology of the system but also to set semantic
attributes at each level necessary for further risk calculation and modeling of integrity violation
scenarios.</p>
        <p>Graph structure. A functional dependency graph is defined as a tuple:</p>
        <p>= (, , Φ  , Φ  ),
•  = {1, 2, ..., }, a finite set of nodes, each of which corresponds to a component of the
system;
•  ⊆  ×  , a set of oriented edges that define the direction of functional or resource influence;
• Φ  :  →  , nodes attribution function;
• Φ  :  →  , edges attribution function.</p>
        <p>Nodes attribution. For each node  ∈  , attribute vector is defined:</p>
        <p>
          Φ  () = (, , , ,  ) ,
•  ∈ [
          <xref ref-type="bibr" rid="ref1">0, 1</xref>
          ], component criticality;
•  ∈ [
          <xref ref-type="bibr" rid="ref1">0, 1</xref>
          ], trust level;
•  ∈ ℛ, functional role;
•  ∈ {0, 1}, reservation availability;
•   ⊆  , area of influence in case of node failure.
        </p>
        <p>Edges attributes. For each edge,  = (,  ) ∈  a set of parameters is set:</p>
        <p>
          Φ  ( ) = (  ,   ,  ,   ,   ) ,
•   ∈ , dependency type (Data, Control, Resource, Temporal, Functional);
•   ∈ R+, time characteristic of communication;
•  ∈ [
          <xref ref-type="bibr" rid="ref1">0, 1</xref>
          ], impact weighting factor;
•   ∈ {0, 1}, direction (0 - unidirectional, 1 - bidirectional);
•   ∈ {0, 1}, sign of degradation.
        </p>
        <p>Formalization of risk spread. The risk transfer along the graph is described by the transformation
operator:
( ) ← (  ) +  · (</p>
        <p>) · ( ) · (1 −   ) ·   ,
• (  ), impact modifier depending on the type;
•  , level of trust in the node  ;
•   , whether the risk is transferred in case of partial degradation.</p>
        <p>Aggregated graph metrics
• Total risk of the system:
total = ∑︁  · ( ).</p>
        <p>∈
• Depth of risk spread, the maximum length of the chain of influence;
• Identification of critical nodes through the product of criticality, number of outgoing links, and
edge weights:</p>
        <p>( ) =  · deg out()·¯ .</p>
        <p>This approach provides the basis for further development of a risk assessment model that takes
into account both the structural topology and semantic characteristics of nodes and links in a hybrid
5G-enabled environment.</p>
      </sec>
    </sec>
    <sec id="sec-6">
      <title>6. Formalization of risk assessment model</title>
      <p>This section introduces a formalized model for cyber risk quantification in hybrid 5G-enabled ICS/OT
networks based on the previously defined Functional Dependency Graph (FDG). The model captures the
semantics of intercomponent dependencies, component criticality, trust levels, timing constraints, and
cascading efects. The proposed approach supports both static and dynamic risk assessment, enabling
scenario-based propagation modeling.</p>
      <sec id="sec-6-1">
        <title>6.1. Node-level risk initialization</title>
        <p>Let the initial risk level for each node  ∈  be defined as:</p>
        <p>
          0() = () ·   · (1 −  ),
•  ∈ [
          <xref ref-type="bibr" rid="ref1">0, 1</xref>
          ] is the criticality of the component,
•  ∈ [
          <xref ref-type="bibr" rid="ref1">0, 1</xref>
          ] is the trust level associated with the node.
        </p>
        <p>
          • () ∈ [
          <xref ref-type="bibr" rid="ref1">0, 1</xref>
          ] is the estimated probability of compromise (based on CVSS score, SIEM alerts, or
        </p>
      </sec>
      <sec id="sec-6-2">
        <title>6.2. Risk propagation via FDG</title>
        <p>The propagation of risk across the graph is defined recursively. For a node  at time , its updated risk
( ) = ( ) +
−1 () ·   · (</p>
        <p>
          ) · (1 −   ) ·   ·   ()
∑︁
∈pred()
(1)
(2)
(3)
(4)
with the following parameters:
•  : normalized edge weight between  and  ,
• (  ): dependency type coeficient (e.g., Control, Data),
•   () ∈ [
          <xref ref-type="bibr" rid="ref1">0, 1</xref>
          ]: temporal impact modifier defined as:
•   ∈ {0, 1}: edge activation indicator (e.g., based on redundancy or failure state),
  () = exp(− · 
 ),
where   is the communication delay or update frequency, and  is a decay parameter.
        </p>
      </sec>
      <sec id="sec-6-3">
        <title>6.3. Threat propagation scenarios</title>
        <p>0() = 1. The propagation is iteratively evaluated over  discrete time steps using:
Let  = {1 , . . . ,  } ⊂ 

denote a set of initially compromised nodes. For each , we initialize
︁(</p>
        <p>︁)
()( ) =  (−1) ( ), ∑︁ (−1) (pred( )) .</p>
        <p>The cumulative risk evolution over time is captured by the matrix:</p>
        <p>R ∈ R| |× ,
where each row corresponds to a node and each column corresponds to a discrete time step. This matrix
captures the dynamics of threat evolution across the graph and allows for temporal analysis, such as
identifying peak risk intervals, delay-sensitive propagation chains, and time-critical influence paths.</p>
      </sec>
      <sec id="sec-6-4">
        <title>6.4. Node and system-level risk metrics</title>
        <p>To support prioritization and mitigation, the following metrics are defined:
• Accumulated Risk Score (ARS):</p>
        <p>() = ∑︁ ()().</p>
        <p>=1
This metric represents the total amount of risk that has been experienced or accumulated by node
 over the entire observation period  . It integrates both direct exposure and indirectly
propagated threats. ARS is useful for identifying persistently afected nodes, even if their instantaneous
risk is low at any specific time.
• Propagation Score (PS):
 () =</p>
        <p>∑︁
∈succ()
 · (
 ) · (1 −   ).</p>
        <p>Propagation Score estimates the ability of a node  to spread risk to its successors succ(). It
takes into account the strength of outgoing functional dependencies ( ), the influence factor
of the dependency type ((  )), and the vulnerability of the target node (via 1 −   ). High PS
values indicate that the node is a potential amplifier of threats and may be critical in cascading
scenarios.
• Critical Impact Index (CII):</p>
        <p>() =  · ( ) · deg out().</p>
        <p>The Critical Impact Index quantifies the strategic importance of node  in terms of its intrinsic
criticality (), cumulative risk over time (ARS), and structural outreach (number of outgoing
edges). It identifies nodes whose compromise could have a high systemic efect, making them
primary candidates for protection and redundancy planning.</p>
        <p>These indices are used to identify high-impact nodes, centrality of propagation, and systemic exposure
levels.</p>
      </sec>
      <sec id="sec-6-5">
        <title>6.5. System aggregation</title>
        <p>Risk can also be aggregated at the subsystem or full-system level:
subgraph = ∑︁ (),</p>
        <p>∈
system = ∑︁ (),
∈
where  denotes the set of nodes in a specific subgraph (e.g., slice, physical zone, MEC region).
(5)
(6)
(7)
(8)
(9)</p>
      </sec>
    </sec>
    <sec id="sec-7">
      <title>7. Implementation and integration architecture</title>
      <p>The Functional Dependency Graph (FDG) will be implemented as a separate service module within the
risk assessment system for 5G-integrated ICS/OT environments. The main function of the module will
be to build an oriented graph  = (, ), where the set of nodes  represents assets and services (PLC,
SCADA, MEC, UPF, etc.), and the edges  are typed dependencies (data, control, resource, temporal,
functional).</p>
      <p>The initial formation of the graph will be done by aggregating data from several sources:
• SCADA/IIoT telemetry, to identify technological connections;
• CMDB/SIEM, for obtaining inventory, trust levels, and topology;
• 5G Orchestrator APIs (e.g., OSM/ONAP), for extracting slice configurations, VNF connections,
and mobile routes;
• network monitoring, to dynamically update current interactions.</p>
      <p>The graph will support real-time updates through an event-driven pipeline that responds to new
devices, slice changes, MEC service activation, or flow switching. Nodes have semantic attributes:
• () — criticality;
•  () — trust;
• () — role in the process (e.g., sensing, control, actuation);
• () — potential impact radius.</p>
      <p>The edges  ∈  are formed with attributes of the type  () ∈
{data, control, resource, temporal, functional}, as well as metadata: delay, frequency, direction,
possibility of degradation. To interact with the Risk Assessment Engine, the graph is exported as an
adjacency matrix with dependency weights, which allows you to model risk propagation in the form of
discrete dynamics on the graph.</p>
      <p>The module will be implemented as a microservice orchestrated via Docker/Kubernetes with a REST
API for integration with other scanner subsystems. This will allow for flexible deployment in MEC
environments, industrial gateways, or cloud-based SCADA. Optimization of graph operations (e.g.,
centrality, shortest path with attributes) is implemented on the basis of the NetworkX or Neo4j Graph
Data Science API frameworks.</p>
      <p>Thus, FDG will act as the core of semantic connectivity in the scanner architecture, allowing move
from point vulnerabilities to complex scenario risk analysis in a heterogeneous environment.</p>
    </sec>
    <sec id="sec-8">
      <title>8. Future work</title>
      <p>The concept of building a functional dependency graph (FDG) and the corresponding risk assessment
model proposed in this paper lays the foundation for the formation of a new approach to vulnerability
scanning in 5G-integrated ICS/OT environments. In further research, it is planned to implement a
full-fledged vulnerability scanner architecture that will integrate the FDG module as the core of scenario
and contextual risk analysis. This area is part of a separate research project dedicated to the creation
of a specialized scanner for hybrid cyber-physical systems, the results of which are currently being
prepared for publication.</p>
      <p>To verify and validate the proposed model, it is planned to build a testbed using 5G network
deployment tools based on open-source components. An isolated laboratory infrastructure has already been
created, which includes open-source implementations of the 5G core and RAN, providing a full-fledged
slice-oriented architecture with the ability to control through an orchestration interface. The experience
of deploying such systems is analyzed in detail in [27, 28], where key platforms are compared and their
performance is evaluated in the context of practical implementation.</p>
      <p>The next step is to connect industrial sensors, PLC emulators, and MEC applications, which will create
a controlled environment for testing FDG construction mechanisms, generating functional dependencies,
and modeling cascading efects in the event of a vulnerability or attack. Such an approach will not only
confirm the operability of the developed model, but will also allow for a quantitative assessment of
the efectiveness of the proposed method in the context of dynamic changes in the topology and 5G
services.</p>
      <p>In the future, it is planned to integrate FDG with machine learning (ML) mechanisms to automatically
interpret event streams, build behavioral dependencies, and detect anomalies. A separate direction will
be to extend the model to multi-segment and inter-network scenarios, taking into account cloud edge
platforms and transitive dependencies between slices or MEC services.</p>
    </sec>
    <sec id="sec-9">
      <title>9. Conclusions</title>
      <p>This paper presents a formalized methodology for modeling functional dependencies in hybrid ICS/OT
environments with 5G integration, and proposes a risk assessment model based on the constructed
functional dependency graph (FDG). The research was motivated by the identified limitations of
existing approaches to cyber risk analysis that do not take into account the dynamic, heterogeneous, and
interdependent nature of modern cyber-physical systems, in particular in the context of 5G architectures.</p>
      <p>The proposed approach provides a unified representation of system components, both physical
(e.g., PLCs, RTUs, sensors) and virtualized (e.g., UPFs, SMFs, MEC applications), in the form of an
oriented graph with node annotation by semantic attributes. The edges of the graph describe typicalized
dependencies: data transfer, control, resource sharing, time constraints, and logical connectivity. This
allows you to model cascading efects and interactions between components.</p>
      <p>A mathematical formalization of the FDG is developed, taking into account the criticality of nodes,
the level of trust, time characteristics, fault tolerance, and radius of influence. This framework serves
as the basis for a risk propagation model that supports both static and scenario analysis. The model
allows you to calculate risk in dynamics, identify critical nodes, and prioritize incident response.</p>
      <p>On the practical side, FDG is planned to implement as a service module that integrates telemetry,
orchestrator data, SCADA topologies, and network configurations. The implementation will be focused
on a microservice architecture with the ability to deploy in MEC environments, industrial gateways, or
cloud-based SCADA systems, using modern graph computing libraries.</p>
      <p>The obtained results confirm the feasibility of using FDG for contextual and dynamic analysis of
cybersecurity risks in next-generation industrial networks. The proposed approach forms the basis for
the further development of a specialized vulnerability scanner focused on ICS/OT+5G environments.</p>
      <p>Future research will focus on integrating FDG with machine learning methods to build behavioral
dependencies, as well as validating the model in a testbed with real devices and MEC applications. A
separate area of focus will be extending the model to multi-segment scenarios, taking into account
inter-network dependencies, slice architecture, and edge cloud platforms.</p>
    </sec>
    <sec id="sec-10">
      <title>Acknowledgments</title>
      <p>This work was supported by the Shota Rustaveli National Foundation of Georgia (SRNSFG)
(NFR2214060) and “Methods of building protected multilayer cellular networks 5G/6G based on the use
of artificial intelligence algorithms for monitoring the country’s critical infrastructure objects” (#
0124U000197).</p>
    </sec>
    <sec id="sec-11">
      <title>Declaration on Generative AI</title>
      <p>The authors have not employed any Generative AI tools.
Applications Security, 2008, pp. 283–296.
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