Black-box Security of White-box Ciphers

White-box cryptography aims to ensure the security of cryptographic algorithms against a white-box attacker. Besides, a white-box cipher should resist against black-box attacks to be assumed secure. Hence, a detailed black-box analysis study for a white-box cipher makes a significant contribution to white-box cryptography. One of the proposed white-box secure block ciphers is SPACE that is based on the Feistel network. Studies on linear and differential cryptanalysis of Feistel Network can be found in the literature, but there is not enough analysis on the SPACE algorithm. The authors of the algorithm have discussed some attacks, including linear and differential attacks. However, especially the linear hull effect can be examined in the SPACE algorithm. According to the previous observation, linear attacks' accuracy can be improved with multiple trails are taken into account. If many trails that are in the same hull can be appropriately constructed, new results can be obtained. Similarly, it can contribute to white-box security by applying other black-box analysis techniques to white-box ciphers.