## 1 Introduction  
Information protection is an important element of human life, from both a private and a professional standpoint. To protect information that is electronically stored or processed, various methods are used, based on solutions that are not always accepted by all users. Those processes can be a source of electromagnetic emissions correlated with the processed information, which become fully useful in the electromagnetic infiltration process. In the TEMPEST evaluation process, all digital signals transferred from the communication ports of the tested equipment are considered to be compromising signals, such as PS/2 port connector [1], USB (Universal Serial Bus ports or peripherals) [2; 3], RJ45 modular connector [4], video signals from VGA (Video Graphics Array), DVI (Digital Visual Interface), HDMI (High-Definition Multimedia Interface) and other display ports [5; 6; 7] or RS232 serial port [8]. Output devices such as printers [9; 10; 11; 12] and video projectors [13] are also being investigated. The video display signal is considered to be the most unsafe in terms of vulnerability to electromagnetic intrusion attacks from all compromising signals that can be emitted by a personal computer. This is also recognized by the TEMPEST procedures [14], which assign to this type of signal the most restrictive corresponding category as a compromising signal. The successive video frames are similar to each other and, for this reason, the video signal has the attributes of a repetitive signal, which means that it is almost periodic [15]. This feature can allow a potential attacker to apply the mediation processes that highlight the video signal, reducing the effect of ambient noise in this way. The effectiveness of the electromagnetic infiltration can be limited in several ways: limiting levels of electromagnetic emissions correlated (having distinctive features) with processed information [14; 15; 16; 17], a disturbance of existing revealing emissions [18; 19] or appropriate shaping of the emission source to eliminate features that enable identification e.g., of text data characters [20; 21; 22]. TEMPEST protection countermeasures now involve hardware modification of Information Technology and Communications (IT&C) equipment by applying shielding measures (shielded housings and shielding window), power and signal filtering, or modifying printed circuit boards in order to minimize the total amount of the equipment electromagnetic radiation and not only those containing information (compromising emanation). This is reflected in the cost of the shielded equipment, which is often 5-8 times higher than the modified commercial equipment. It is true that the security of sensitive information is related to national security issues and must be applied regardless of the costs involved, but maintaining the level of security of this information with reducing costs is the target of the TEMPEST protection measures, which is specified by official documents as the \"protection zone model\". The disturbance of existing revealing emissions does not lower the levels of these emissions. It introduces additional sources of electromagnetic disturbances, some of which can reach significant levels. This solution is not recommended, due to the deliberate introduction of additional sources of electromagnetic emissions into the environment. Shaping the sources of such emissions is another method that limits the effectiveness of electromagnetic infiltration. This is achieved by changing the colors of the text and the background. An appropriate selection of color pairs may reduce the effectiveness of the source of unwanted emissions [15; 16]. However, this method is not universal from the point of view of application in video standards. A certain properly selected text and background color pairs can be effective for the analogue VGA standard, but, in the case of the digital DVI (HDMI) standard, the efficiency of a color pair may not be so obvious [16].