Ireneusz Kubiak

Ireneusz Kubiak

Computer fonts can be one of solutions supporting a protection of information against electromagnetic penetration. This solution is called -Soft TEMPEST-. However, not every font has features which counteract the process of electromagnetic infiltration. The distinctive features of characters of font determine it. This article presents two sets of new computer fonts. These fonts are fully usable in everyday work. Simultaneously they make it impossible to obtain information using the non-invasive method. Names of these fonts are directly related to the shapes of the characters. Each character of these fonts is built only with vertical and horizontal lines. The differences between them consist in the different widths of the vertical lines. The Symmetrical Safe font is built from vertical lines with the same widths. The Asymmetrical Safe font is built from vertical lines with two different widths of lines. However, the appropriate proportions of the widths of the lines and clearances of each character of the safe font have to be met.

Ireneusz Kubiak, Joe Loughry

Protection of information against electromagnetic eavesdropping is an important issue. Information may be derivable from the shape of an unintended electromagnetic signal. The resulting electromagnetic emanations can be correlated with processing of classified information. The problem extends to computer printers. This article presents a technical analysis of LED arrays used in monochrome computer printers and their contribution to unintentional electromagnetic emanations. We analysed two printers from different manufacturers, designated $A$ and $B$. The forms of useful signals and their dependence on parameters of printing data are presented. Analyses were based on realistic type sizes and distribution of glyphs. Pictures were reconstructed from received radio frequency (RF) emanations. We observed differences in legibility of information receivable at a distance that we attribute to different ways used by printer designers to control the LED arrays, particularly the difference between relatively high voltage single-ended waveforms and lower-voltage differential signals. To decode the compromising emanations required knowledge of---or guessing---printer operating parameters including resolution, printing speed, and paper size. The optimal RF bandwidth for detecting individual pixels has been determined. Measurements were carried out across differences in construction and control of the LED arrays in tested printers, and the levels of RF emissions compared for selected operating modes (fast, high quality, or toner saving mode) of the printing device.