## 4 Countermeasures against Thermal Covert Channel Attacks  
Our proposed work has different steps to detect and fight against such thermal covert channel attacks. For the detection step, we used frequency scanning-based detection, which was presented by [PERSON] et al. [3; 5].  
* Step 1 (Detection): The detection algorithm uses the module of bandpass filtering to filter out the thermal signals that are out of every band of interest. The detection algorithm is also designed in a way that it can manage TCC, whose receiver and transmitter runs through two different channels. While designing the countermeasure method, we consider that the receiver and the transmitter have access to the same thermal data files, and also that the transmitter and the receiver threads are both suited in the same physical core and share the same thermal sensors, known as Intra-core channel [3; 5]. The frequency scanning process is used to detect any existing TCC channels.  
In addition, each core specifies the signal's maximum amplitude from the frequency scanning process and leads it into a module known as the decision-making module. The decision-making module compares the signal's amplitude against a threshold \(\rho\) (\(\rho\) is the pre-set threshold for the signal amplitude in a detection cycle.) and decides whether a signal (e.g., 1 0 1 0) is from a covert channel or not. If the amplitude of the signal is higher than \(\rho\), an attack is present; otherwise, there is no attack happening. Statistically, the threshold \(\rho\) is selected experimentally to be 0.02 dB [5]. Based on frequency scanning, if the defender, denoted as, global manager, identified the TCC channel exists, the proposed countermeasure is applied;
* Step 2 (Classify bits): For applying the proposed countermeasure, we need to classify bits into \"1\" and \"0\" according to the thermal signal changes. In our work, the bit \"1\" represents changes in the thermal signal, while the bit \"0\" illustrates no changes;
* Step 3 (Check bits): For this step, the system checks if the bit is \"1\" or not by considering the changes in the thermal signal. Then, if the bit is \"1\" the operation will start;
* Step 4 (Adding an extra noise): The last step is adding an extra noise to the temperature signal, which results in generating more heat to the system where the bit is \"1\", therefore, there is no bit change for a long duration, as Figure 4 shows.  
In the proposed method, once a core is determined to be associated with a thermal covert channel, a countermeasure shall apply to fight any future thermal covert channel transmission. Here we assume that a thermal covert channel thread is running on a dedicated logical core all over a full communication session.  
We add extra noise to the thermal signal to generate more temperature when the thermal signal is at high temperature (\(t_{h}\)), which results in increased duration of \(t_{h}\) and changing the pattern of the thermal signal and making it secure.  
Note that the global manager cannot immediately apply countermeasure to control the suspicious core. First, the global manager scales down the temperature of the suspicious core for a few seconds (e.g., 0.5 s) to decrease the risk, and then a countermeasure is implemented to block any future TCC transmission [3; 5]. As for the simulation results, from Figure 5, one can see that the average temperature of a thermal signal without countermeasure is around 72 \({}^{\circ}\)C (Figure 5a) and when the countermeasure is applied the average temperature increases to 76 \({}^{\circ}\)C (Figure 5b).