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  <front>
    <journal-meta />
    <article-meta>
      <title-group>
        <article-title>Building cybersecurity systems in hybrid cloud ecosystems based on discrete-event simulation</article-title>
      </title-group>
      <contrib-group>
        <contrib contrib-type="author">
          <string-name>Iryna Tregubenko</string-name>
          <xref ref-type="aff" rid="aff1">1</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Emil Faure</string-name>
          <email>e.faure@chdtu.edu.ua</email>
          <xref ref-type="aff" rid="aff0">0</xref>
          <xref ref-type="aff" rid="aff1">1</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Viktor Kotetunov</string-name>
          <email>v.kotetunov@gmail.com</email>
          <xref ref-type="aff" rid="aff1">1</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Yevhen Morshch</string-name>
          <email>yevhen.phd@gmail.com</email>
          <xref ref-type="aff" rid="aff1">1</xref>
        </contrib>
        <aff id="aff0">
          <label>0</label>
          <institution>Cherkasy State Technological University</institution>
          ,
          <addr-line>Shevchenko Blvd., 460, Cherkasy, 18006</addr-line>
          ,
          <country country="UA">Ukraine</country>
        </aff>
        <aff id="aff1">
          <label>1</label>
          <institution>State Scientific and Research Institute of Cybersecurity Technologies and Information Protection</institution>
          ,
          <addr-line>M. Zaliznyaka Str., 3/6, Kyiv, 03142</addr-line>
          ,
          <country country="UA">Ukraine</country>
        </aff>
      </contrib-group>
      <abstract>
        <p>The nature of threats and vulnerabilities of information complex systems and hybrid cloud ecosystems in cyberspace is complex, heterogeneous, multifactorial, flexible and rapidly modifiable. Traditional approaches to building security systems do not take into account many threats that are not obvious from the user's point of view. To study and develop new approaches to building reliable data protection systems and analyze their efectiveness, the vulnerabilities of confidential data in modern cloud environments are assessed, taking into account the modification of modern types of software architecture. Particular attention is paid to the features of microservice software architecture and their impact on the vulnerabilities of cloud ecosystems. It is proposed to use discrete-event simulation approaches to modeling security systems, taking into account the characteristics of hybrid cloud ecosystems.</p>
      </abstract>
      <kwd-group>
        <kwd>eol&gt;cybersecurity systems</kwd>
        <kwd>cloud</kwd>
        <kwd>data protection</kwd>
        <kwd>microservice architecture</kwd>
        <kwd>discrete-event simulation</kwd>
      </kwd-group>
    </article-meta>
  </front>
  <body>
    <sec id="sec-1">
      <title>1. Introduction</title>
      <p>Cloud technologies have a sustainable development, are constantly modified, in particular in terms of
increasing the speed of computing, expanding the capabilities of analytics, and the wider use of big
data and artificial intelligence [ 1, 2]. The nature of threats and vulnerabilities of information complex
systems and hybrid cloud ecosystems in cyberspace is complex, heterogeneous, multifactorial, flexible
and rapidly changing. Traditional approaches to building security systems do not take into account
many threats that are not obvious from the user’s point of view.</p>
      <p>In order to research and develop new approaches to building reliable data protection systems and
analyze their efectiveness, it is necessary to conduct a thorough assessment of vulnerabilities of
confidential data in modern cloud environments, taking into account the modification of modern types
of software architecture, in particular the impact of the popular microservice architecture of software
tools on the vulnerabilities of cloud environments, and to propose appropriate technologies for modeling
protection systems, taking into account the characteristics of hybrid cloud ecosystems.</p>
    </sec>
    <sec id="sec-2">
      <title>2. Related works</title>
      <p>Ensuring security in cloud environments remains a pressing issue against the backdrop of the growing
dependence of supporting the vital processes of the information society on cloud platforms and services
based on cloud environments.</p>
      <p>In addition, the large amounts of data already stored in popular clouds such as Azure, Amazon,
Google Cloud, etc. are constantly increasing and will contain a significant portion of files with
confidential information, including configuration files, API keys, credentials, etc. The problem of leakage of
conference information due to incorrect settings of cloud segments remains and can lead to security
breaches and unauthorized access to various cloud services such as databases, cloud infrastructure,
third-party APIs, etc.</p>
      <p>Modern software, most applications, are not developed from scratch; some of the necessary functions
are used from the ready-made functionality of other services, often cloud-based. At the same time, access
to services is protected by various types of credentials: passwords, tokens, usernames, certificates,
API keys, etc. In turn, such confidential credentials may not be reliably protected at the software
development stage. As a result, the likelihood of misuse of resources and unauthorized access to
information increases significantly and can lead to critical consequences [ 3, 4]. Examples are known.
Many researchers confirm frequent leaks of confidential data through various channels [3, 5, 6, 7]:
• modern version control platforms;
• virtual server images;
• incorrectly configured cloud storage;
• large language models based on code sharing platforms;
• mobile applications;
• mini applications, micro services;
• Docker containers, etc.</p>
      <p>
        In addition to quantifying confidential data leakage, studies suggest various approaches to increasing
the eficiency of detection processes [
        <xref ref-type="bibr" rid="ref18 ref23 ref9">8, 9, 10, 11</xref>
        ], which can be useful for further improving methods
and models of data protection in cloud environments.
      </p>
    </sec>
    <sec id="sec-3">
      <title>3. Features of protecting cloud applications with microservice architecture</title>
      <p>The transition to new software architectures is leading to an increase in the problem of confidential
data leakage and end-user losses. It is interesting to investigate the efectiveness of security processes in
applications and platforms based on microservice architecture. Such hybrid ecosystems consist of many
elements: the parent application server, the developer server, the hosting service, the services used
by the developers, the client application, etc. A mandatory component of the joint eficient operation
of all these elements is their constant joint authentication, which difers from user authentication on
the platform or in applications. This is a type of technical authentication that allows an attacker to
access various services on behalf of developers, which can be a significant vulnerability in the context
of currently used insecure software development practices.</p>
      <p>For example, research [7] has shown that a significant number of WeChat (over 36 thousand detections)
and Baidu (112 detections) microservices and applications have non-obvious vulnerabilities related to
development technologies and features of the chosen architecture. Most often, this is due to the so-called
hard auto-identification used by developers. Undoubtedly, this causes quite significant security issues,
including privacy violations for both developers and users. A study [7] confirmed the conclusion that
any knowledgeable attacker on the network can make it impossible for an application to work, even if
they do not have their own account on the parent platform. Also, such an ofender will potentially have
the opportunity to engage in phishing, gain access to confidential information, and send out mailings
to platform users.</p>
      <p>Thus, the analysis shows that the nature of threats in cyberspace is heterogeneous, multifactorial,
lfexible, and rapidly changing. Traditional algorithms for detecting all threats at each access point and
in each user application, including in the cloud environment, and neutralizing them are not efective. To
research and develop new approaches to building data protection systems and analyze their efectiveness,
there is a need to develop new approaches to modeling such systems, taking into account the features
of integrated cloud environments.</p>
    </sec>
    <sec id="sec-4">
      <title>4. Research of methods for modeling a data protection system based on DES principles for hybrid cloud ecosystems</title>
      <p>Usually, when modeling protection systems, it is proposed to use continuous modeling methods. The
main features of which are as follows:
• The system is considered to be constantly changing in time;
• Time is the main parameter and often the criterion;
• Models continuously track the state of the system in the time dimension.</p>
      <p>It is suggested to change the viewing angle. Continuous monitoring or modeling of a complex hybrid
ecosystem is a complex and resource-intensive task. It is proposed to investigate the possibility of
applying a discrete approach to modeling systems with continuous information processes, in particular,
to consider the principles of DES modeling.</p>
      <p>Usually, Discrete-Event Simulation (hereinafter referred to as DES) considers a system as a sequence
of events in time. It is assumed that events occur at certain points in time, separated from each other.
The basic features of DES modeling can be identified:
• An event occurs at a specific time point. As defined above, DES is used to model systems, processes,
and flows that can change at identifiable points in time. At the same time, DES will not track the
state of flows, systems, processes between these moments of time, i.e. continuously.
• Focus on events. That is, DES focuses on events that change the state of the system.
• Skipping time intervals between events. DES does not investigate the state of the system between
the moments of time when the event occurred, which reduces the complexity and the amount of
resources required for modeling processes. During the modeling process, DES moves from one
event to the next, the next.
• Widespread use of queueing theory. This is not a mandatory feature of DES, but in cases where
the processes of receiving and servicing requests are significant in the system, the use of queue
theory is more than reasonable. Unlike continuous modeling, the main features of DES are as
follows:
• No changes between events
• The main parameter is not time, but an event
• The state of the system between moments of time does not matter.</p>
      <p>When modeling data protection in complex heterogeneous systems, including hybrid cloud
ecosystems, we assume that:
• From the point of view of functional suitability, the state of protection systems is significant at
the time of a cyber incident, attack, unauthorized access attempt, etc.
• Outside of the moments of attack and intrusion attempts, the state of the protected system is
unimportant.</p>
      <p>At the same time, such a system can be considered as discrete, and the event that will afect the
change in the system state is the moment of attack, and there is a finite set of such moments. Figure
1 shows the DES process of a data protection system in hybrid cloud ecosystems as a discrete-event
system.</p>
      <p>The properties of data protection systems in hybrid cloud ecosystems identified by the authors
allow us to attribute them to discrete-event systems, which are most widely used in the theory of
automata with their variants, such as various graphs and the mathematical apparatus of Petri nets. The
latter has an intuitive graphical representation, has been widely used in applied problems of modeling
asynchronous and parallel dynamic systems, and has algorithmic developments.</p>
      <p>In the classical representation [12], a Petri net has four components:
 = (,  ,  , )
(1)
where:
 = {1, 2, 3, ..., } is a finite set of positions,  &gt;= 0 is the power of the set  ;
 = {1, 2, 3, ..., } is a finite set of transitions,  &gt;= 0 is the power of the set  ;
 ∩  = ∅ - the sets  and  do not intersect.
,  = 1, 2, ...,  - any element of  ;
 ,  = 1, 2, ...,  - any element of  ;
 - is an input function that represents the transition of  to the set of positions ( );
 - is an output function that represents the transition of  to the set of positions ( ).</p>
      <p>Thus, the structure of a Petri net is defined by its positions, transitions, input and output functions,
and is usually represented as a graph. Such a graph is a bipartite, oriented multigraph, in which one
part is formed by positions and an arc by transitions. Many arcs connect positions and transitions. In
such a graph, there are two types of nodes: a position (denoted by a circle) and a transition (denoted
by a bar). Arcs are oriented and connect positions and transitions. An arc that has a direction from
position pi to transition tj determines the position that is the output of the transition.</p>
      <p>In the further development of distributed modeling methods, the models and structure became more
complex, high-level networks, nested, functional, hierarchical, etc. appeared. A characteristic feature
was often the modular representation of diverse distributed systems, with the allocation of a separate
autonomous module that functioned independently, had a certain internal state (whether dynamic
or stable) and a certain set of inputs and outputs. The inputs/outputs were used to interact with the
external environment.</p>
      <p>To solve the problem of modeling protection systems, it is necessary that such a functional module
can be located separately from the basic system.</p>
      <p>We will impose certain restrictions: we will assume that external influences from the environment
are directed exclusively to the set of inputs, and the result can be considered exclusively in the set of
outputs. This approach is inherent in functional networks, which have a more regular structure in the
presence of these restrictions.</p>
      <p>= (, , , ,  ,  )
(2)
where:
 = {1, 2, 3, ..., } is a finite set of positions,  &gt;= 0 is the power of the set  ;
 = {1, 2, 3, ..., } is a finite set of transitions,  &gt;= 0 is the power of the set  ;
 ∩  = ∅ - the sets  and  do not intersect.
,  = 1, 2, ...,  - any element of  ;
 ,  = 1, 2, ...,  - any element of  ;
 - is an input function that represents the transition of  to the set of positions ( );
 - is an output function that represents the transition of  to the set of positions ( ).
  ⊆  - is the set of input positions of the Petri net;
  ⊆  - is the set of output positions of the Petri net.
  ∩   = ∅ - the sets   and   do not intersect.</p>
      <p>With this approach, another set PV is formed - the set of internal positions that are not included in
the sets PI and PO.</p>
      <p>Given that the defense systems under consideration will receive heterogeneous threats at the input
positions and will require diferent times for the defense system to react, our model needs to include
time delays for threat processing and determine the moment when the DES process is initiated. Let’s
get the model:
   = (, , , ,  ,  , ,  )
(3)
where:
 = {1, 2, 3, ..., } is a finite set of positions,  &gt;= 0 is the power of the set  ;
 = {1, 2, 3, ..., } is a finite set of transitions,  &gt;= 0 is the power of the set  ;
 ∩  = ∅ - the sets  and  do not intersect.
,  = 1, 2, ...,  - any element of  ;
 ,  = 1, 2, ...,  - any element of  ;
 - is an input function that represents the transition of  to the set of positions ( );
 - is an output function that represents the transition of  to the set of positions ( ).
  - is the set of input positions of the Petri net;
  - is the set of output positions of the Petri net.
 - time delay for threat processing;
 - is a position label that characterizes a certain state of the model.</p>
      <p>It is also possible to increase the eficiency and accuracy of the analysis and the corresponding model
built on the basis of hierarchical Petri nets. In this case, the same Petri nets can act as constituent
elements. In the task of ensuring data protection in hybrid cloud environments, each nested element
can identify diferent types of threats and/or perform direct protection actions. The mathematical model
in this case will be as follows:
  = (, , , , 0, , , )
(4)
where:
 = {1, 2, 3, ..., } is a finite set of positions,  &gt;= 0 is the power of the set  ;
 = {1, 2, 3, ..., } is a finite set of transitions,  &gt;= 0 is the power of the set  ;
 ∩  = ∅ - the sets  and  do not intersect.
,  = 1, 2, ...,  - any element of  ;
 ,  = 1, 2, ...,  - any element of  ;
 - is an input function that represents the transition of  to the set of positions ( );
 - is an output function that represents the transition of  to the set of positions ( ).
0 - is the set of initial labeling of the network;
 - is the set of nested Petri nets in ;
 - is the set of input positions of nested Petri nets;
 - is the set of output positions of nested Petri nets.</p>
      <p>The developed model, among other things, can allow analyzing the dynamics of the system being
modeled.</p>
    </sec>
    <sec id="sec-5">
      <title>5. Discussion</title>
      <p>Is it enough to focus on the approaches proposed in this article for the problem under consideration?
Certainly not. The research will continue. It would be advisable to consider other approaches for
modeling complex security systems in cloud heterogeneous ecosystems that will allow first to efectively
model and then find a platform for building such systems, taking into account the rapid changes in IT
technologies, the growth of processed data, the development of quantum technologies, etc. Sustainable
search for appropriate solutions will contribute to the development of more efective data protection
technologies in complex systems and hybrid cloud ecosystems, which will generally contribute to the
creation of a more secure cyberspace.</p>
    </sec>
    <sec id="sec-6">
      <title>6. Conclusions</title>
      <p>The article reveals the complex and multifactorial nature of threats and vulnerabilities of information
large systems and hybrid cloud ecosystems in cyberspace. The following properties of such systems are
important to take into account: heterogeneity, hierarchy, multifactoriality, flexibility, and high speed of
complex changes. Traditional approaches to building defense systems and corresponding algorithms
are not efective enough and usually do not take into account a whole group of threats associated with
the architectures of the developed defense systems.</p>
      <p>To research and develop new approaches to building data protection systems in hybrid cloud
ecosystems and analyze their efectiveness, it is proposed to use DES technologies to model protection systems,
taking into account the characteristics of hybrid complex systems.</p>
    </sec>
    <sec id="sec-7">
      <title>Declaration on Generative AI</title>
      <p>The authors have not employed any Generative AI tools.
[1] I. B. Tregubenko, V. Y. Kotetunov, Problems of information security of hybrid integration
ecosystems based on cloud technologies, in: Proceedings of the III International Scientific and Practical</p>
    </sec>
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