The FESH algorithm is a block cipher algorithm based on finite field operations. Currently, no research has been conducted on its side-channel attack security. Therefore, this study proposes two methods to address this issue: a correlation power analysis attack method targeting the FESH algorithm, and a template attack method based on an improved TransNet model. The first method theoretically analyzed the vulnerabilities of the FESH algorithm and successfully obtained valid leaked information through a correlation power attack; The second method introduced BlurPool blurring and downsampling techniques, as well as normalization operations, which reduced the training parameters of the improved model by approximately 50%. Additionally, the validation was performed on both the FESH dataset and the desynchronized ASCAD public dataset, which provided evidence that the entropy estimates were significantly better than those of the original TransNet model. The experimental results highlight the importance of considering side-channel security when implementing the FESH algorithm.
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