Use Case 2: Template Attack Using Two Devices in Profiling Phase Sample Clauses

Use Case 2: Template Attack Using Two Devices in Profiling Phase. In order to improve the performance of the portable template attack, we try building templates with two different devices and attacking a third one. Thus, a model is built with 20 000 profiling traces from D1 and 20 000 profiling traces from D2. The traces are preprocessed as in previous experiments and the SOST function is calculated (Fig. 13, Device 1+2). This figure, when compared with the SOST of each device separately (Fig. 11), suggests that the new SOST is a combination of the other two. We select 7 POIs in each one of the significant spikes ([95, 142, 153, 173, 207, 218, 237]) and generate the 256 templates. In the attacking phase 1 000 power traces of devices D1 and D2 storing a fixed 8-bit value are used (500 from each one). Then the model is applied and the fixed value is guessed. The results of this non-portable attack using two devices for profiling are excellent and they can be seen in Table 4 (Step 0, [D1+D2] vs [D1+D2]). For the portable attack, the model is applied to 1 000 power traces from D3 storing the same fixed value. As it can be seen in Table 4 (Step 0), the results are quite bad because the model does not suit this device. The same happens with D4. As in the first use case, the similarity assessment method is applied. Thus, 20 000 power traces from the third and fourth device storing random 8-bit values are taken and labeled with the stored value. The traces are preprocessed and the SOST function is calculated (Fig. 13, D3 and D4). We can see that both shapes are completely different and hence the attack is not successful because we are not selecting representative POIs for all the devices. To improve the POI selection, we apply our technique, as shown in Sec. 5.2. First, we analyze the performance of each POI individually (Table 4, Step 0). Note that the results are almost the same in D3 and D4 because these devices are very similar. Then, different combinations of the 7 POIs are tested (Table 4, Step 2). The combination which throws best results is 2+3+6. After that, we try to adjust the POI of interest, achieving the attack using the points [143, 157, 217] (Table 4, Step 3).