# Protecting Data at Risk of Unintentional Electromagnetic Emanation: TEMPEST Profiling
## 4 From van Eck Phreaking to TEMPEST Profiling
### RED/BLACK Separation and Filtering  
Careful design can greatly reduce conductive information leakage by properly filtering and suppressing power supplies and signal cables [89]. The RED/BLACK separation is a TEMPEST security strategy for separating systems, components, cables, and circuits handling sensitive information from those that do not [44]. The NSA uses the term base-band RED signal to describe compromising emanations that can reveal national security information. RED is a generic term referring to conductors, optical fibers, components, devices, and systems transmitting unencrypted and classified defense signals and the areas where those signals occur. The TEMPEST specification can be applied to RED devices as protection against EM leakage. BLACK is a generic term describing conductors, optical fibers, components, equipment, or systems transmitting unclassified or encrypted signals and the areas where those signals occur. It is necessary to separate the part processing the RED information and the part processing the BLACK information. The RED/BLACK concept allows for defining the architecture and needs of TEMPEST protection, the protective device type, and these device locations. The goal is that an unauthorized entity can only access BLACK information (Figure 3) [90]. Several designs need to be considered to ensure physical and logical RED/BLACK separation and minimize the risk of data leakage and compromise. One aspect is efficient cable management within the RED/BLACK engineering installation. This includes using separate conduits, pathways, or dedicated cable trays for RED and BLACK cables. The possibility of data leakage is significantly reduced by physically separating the cables. Another \begin{table}
\begin{tabular}{c c c} \hline \hline
**Zone** & **Distance** & **Environment** \\ \hline Zone 0 & Up to 1 m & An attacker is expected to have almost immediate access. \\ \hline Zone 1 & \(\sim\)20 m & An attacker’s access or building materials provide attenuation equivalent to 20 m. \\ \hline Zone 2 & \(\sim\)100 m & Free space or building materials provide attenuation equivalent to 100 m. \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Level of protection according to zones. Figure 3: RED/BLACK separation (source [90]). key factor is the careful selection and configuration of equipment. Routers, switches, and firewalls play a vital role in ensuring the secure flow of information. Proper configuration of these components is essential to preventing data leakage. Maintaining RED/BLACK separation requires robust network architecture. This can be achieved by using separate networks, virtual local area networks (VLANs), or physically isolated network segments. The author of [91] described the concept of separating classified and unclassified information as a RED/BLACK separation through physical distance and the implementation of appropriate shielding measures. According to NSTISSAM TEMPEST/2-95 (the document specifies the shielding or minimum physical distance between wires or equipment that transmits or processes RED and BLACK signals), RED and BLACK computers should be kept a minimum distance of \(1\) m (39 inches) from each other. In [92], however, the authors demonstrated a technique for effective communication over this distance. This technique used silent high-frequency sounds emitted by the target device speakers to transmit data to a nearby computer equipped with a microphone. The authors of [93] introduced RED/BLACK separation within the power supply. The uninterruptible power supply (UPS) was tested to evaluate asymmetric, symmetric, and non-symmetric isolation. The results indicated an exceptional level of isolation that, in combination with the existing power transmission line filters in the equipment, adequately met the necessary isolation requirements for RED/BLACK separation.