# Side Channel Leakages Against Financial IC Card of the Republic of Korea +
## 3 Evaluation Methodology for the Financial IC Card Protocol
### Security Evaluation Methodology of Side Channel Analysis Under Black Box Model
#### 3.2.3 Recovering the Master Key via Some Round Keys
Finally, the master key was recovered via the brute force attack defined in Algorithm 1. ### Identifying the Public Information

This section elaborates upon the security evaluation methodology defined in Figure 3, except for the defined enumeration. For this, the experimental setup described in Figure 2 was utilized. In Figure 4, three identical areas should be identified, due to the \(DEA\) algorithm being computed three times in the financial IC card protocol. Therefore, when performing correlation power analysis, the plaintext or ciphertext information was searched through until the occurrence of a peak. Due to time and memory limitations, not all points can be collected simultaneously. Thus, a proportion of all points should be measured after estimating the plaintext/cipher operation. Finally, the \(DEA\) algorithm operation in the red box of Figure 4 was found. Figure 3: Security evaluation methodology for financial IC card protocol. In particular, block cipher SEED was composed of 16 rounds. However, 16 identical rounds cannot be found in Figure 5. It can be estimated that the area of dimensions \(0.9\times 10^{4}\) to \(1.5\times 10^{4}\) is divided into 12 identical areas. There are also two identical areas in the front and rear of the middle part. Therefore, it can be estimated that some countermeasures are applied to 1, 2, 15, and 16 rounds. Additionally, the plaintext information was revealed in the front part in Figure 6. The detailed description is given in the next section. In order to analyze the plaintext operation, the front part of the \(DEA\) algorithm operation was re-collected. Additionally, as shown in Figure 3, the plaintext operation was analyzed by repeating trial-and-error to obtain the best solution. The best solution is as follows. Figure 4: Measured trace when performing the financial IC card protocol. Figure 5: A trace for the \(DEA\) algorithm. Figure 6: Result of correlation power analysis with plaintext information. * Compression scheme: sum of squares
* Compression Ratio : 800

The sum of squares scheme indicates that \(N\) points were squared and summed up to a single point, where N implies the compression ratio. All 16 bytes of plaintext were analyzed at the front part of the foremost \(DEA\) operation. The alignment based on correlation was performed as a default pre-processing scheme with extensive trial-and-error. Finally, the best solution was obtained. Afterwards, the best solution was utilized to perform side channel analysis for a main target. ### Security Evaluation for Financial IC Card Protocol

As shown in Figure 3, the security for a financial IC card, including state-of-the-art attack schemes described in Section 3.2.1, was evaluated. Before performing the side channel analysis defined in Section 3.2.1, the applied countermeasure was estimated in block cipher SEED by investigating some power traces. As discussed in Section 4.1, it can be estimated that some countermeasures may be applied to only 1, 2, 15, and 16 rounds in the \(DEA\) operation of Figure 5, since the middle part can be divided into 12 rounds. Additionally, 1, 2, 15 and 16 rounds were thicker than the middle part. The first round can be split into three parts, due to the identical operation being repeated three times in 1 round. Therefore, the first part of 1 round can refer to the red box in Figure 5.

Five different behaviors were also confirmed in all the collected traces. As seen in Figure 7, the different points are the middle part of the five behaviors. The middle part of the first behavior is composed of four negative peaks. By the same logic, the middle part of the fifth behavior consists of eight negative peaks. The second, third, and fourth behaviors also have same features. Naturally, it was predicted that these behaviors may be connected to S-box operation, since the G-function of the first round has four S-box operations. It seems that the random dummy operation may be applied to that if this computation is a real S-box operation.