نوع مقاله : مقاله پژوهشی
نویسندگان
1 استادیار، گروه امنیت شبکه و رمزنگاری، پژوهشکده فضای مجازی، دانشگاه شهید بهشتی، تهران،
2 کارشناس ارشد مخابرات امن و رمزنگاری، پژوهشکده فضای مجازی، دانشگاه شهید بهشتی، تهران
چکیده
کلیدواژه‌ها
عنوان مقاله [English]
نویسندگان [English]
Impossible differential attack is one of the strongest methods of cryptanalysis on block ciphers. In block ciphers based on SPN (substitution permutation network), the only layer that resists the difference is the nonlinear layer. Obviously, paying attention to the features of nonlinear layer is important for the sake of preventing statistical attacks, such as the differential attack. Therefore, this layers’ features regarding attack tolerance should be carefully investigated. The existence of such a nonlinear layer with the required features and applying it in the entire length of the block can lead to more resistance against differential attacks. Over the past few years, a new set of block ciphers based on SPN has been introduced, in which the nonlinear layer is applied only to a particular part of the state. In this paper, a general framework for finding the characteristics of the impossible difference in this type of new block cipher is presented. Contrary to the previous miss-in-the-middle methods, which are used to find the impossible differences, the method presented in this article is independent of the feature of linear layer of the algorithm and allows the attacker to systematically find the effective impossible differential even in cryptographic algorithms with highly complex linear layer. In order to demonstrate the efficiency of the proposed method, the family of LowMC ciphers that use bitwise linear layer are examined in this paper and based on this framework some impossible differential characteristics are proposed for some versions of reduced LowMCs. This proposed impossible differential characteristics can be easily applied in key-recovery attacks based on the framework presented in this paper. As an example, we show that based on the impossible difference characteristic obtained for 63 rounds of the LowMC (128,128,2,128), a key-recovery attack is applied to the 64-round of this algorithm. In proposed attack, the complexity of memory is 289, the complexity of the time is 2123.7, and the complexity of the data is equal to 2123.1 of the chosen plain text.
کلیدواژه‌ها [English]
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