# Evaluating the Functioning Quality of Data Transmission Networks in the Context of Cyberattacks
## 1 Introduction
The technique of replication through removable media, i.e., moving over the network using removable devices, was used in cyberattacks of a cybergroup called the \"Equation Group\", which is one of the most powerful groups and has functioned since 2001. It was discovered by the Russian company Kaspersky Lab. The cybergroup was named the \"Equation Group\" because their members actively used encryption algorithms, advanced masking methods and other smart technologies. The Fanny Trojan created a hidden section on a USB drive, where the commands were recorded as received from the control server. When an employee connected a USB flash drive to a computer of an isolated network, these commands were executed automatically. The Equation Group used a zero-day vulnerability in the.lnk file handler, so autorun shutdown on removable devices could not stop the Trojan spreading. The collected data were again written in the hidden section of the USB flash drive, and then, when the USB flash drive was connected to a computer with Internet access, the data were transmitted to the malefactors' server [2]. By carrying out cyberattacks on automated systems and technological DTNs, malefactors disrupt the normal functioning of the power complex elements [3]. Therefore, the automation systems and technological DTNs that are being implemented in power complexes must provide operational management of energy resources, as well as meet the high cybersecurity requirements for both automation system elements and technological DTNs. Therefore, the task of evaluating the quality of the functioning of the technological DTN of the energy complex is relevant when a malefactor implements cyber actions. This paper proposes and discusses one of the possible mechanisms to measure the impact of cyberattacks against the network elements of a technological DTN when assessing the quality of its functioning by the value of the probability of the successful delivery of data packets that provide control of the power complex elements. By means of the mathematical tools of graphical evaluation and review technique (GERT) networks [4; 5; 6], the paper proposes a novel method, the essence of which is to represent the process of the functioning of the data transmission network, when malefactors realize a cyberattack, as a stochastic network, to specify the type of individual distributions, to determine an equivalent function, with the initial and central moments of distributions of the original random values calculated by means of numerical methods and specification of the final distribution function of the data packets' delivery time. The method proposed by the authors allows one to remove restrictions on the type of distributions which are used as original ones, and this method is free from the assumptions, indicated in [7; 8], about the exponential distribution of the duration of packet waiting and service (transmission) in modern technological data transmission networks. The novelty of the proposed method lies in defining the parameters of the quality of the service of the network in the context of cyberattacks in the absence of restrictions on the type of distribution functions of the transmission time, the duration of the successful realization of cyberattacks, the recovery time of the network elements and the type of network traffic. The paper proposes the following new results:  
* a mechanism taking into account the influence of cyberattacks on the quality parameters of a technological DTN is developed;
* a set of expressions for calculating the values of the distribution function and the times of the delivery of data packets in cyberattack conditions is obtained in an explicit form;
* the sensitivity of the results obtained on the type of traffic in the technological DTN is shown. The rest of the paper is structured as follows. Section 2 reviews relevant papers on the research topic. Sections 3 and 4 describe the theoretical foundations of the proposed approach: Section 3--the problem statement, Section 4--the method to measure the impact of cyberattacks.