The Differential Analysis On Lightweight Block Cipher RECTANGLE

The design and analysis of the lightweight block cipher is the hotspot problems in the field of information security. Differential cryptanalysis is one of the most effective ways to attack iteration block cipher. This paper mainly discusses the differential analysis of lightweight block cipher, designs the algorithm of searching biggest differential characteristics. And we use the search algorithm to attack RECTANGLE. In order to achieve a better differential resistance performance, the Permutation layer is improved.First we discuss what the design characteristics of the lightweight block cipher is. The data throughput is small because limited resources environment just need a small scale of processing data. Also limited resources environment require weak security. Again in addition to security, we should consider the space and efficiency needed for the hardware implementation of algorithm in resource-constrained environments. Therefore, the design of lightweight algorithm is mainly the game between security and efficiency. Usually, we can use two methods to design lightweight block cipher. The first one is to improve the existing algorithm, which only need small amount of work and its security analysis is easy. Since the different original algorithm need different environment, the improved algorithm may appear new problems. The second one is to design a new lightweight algorithm, which requires large workload and its security analysis is difficult. But the limitation of the new algorithm has not been fixed before, the designer can use some ways to make it more possibly accord with the standard of lightweight.Differential cryptanalysis is a kind of chosen-plaintext attack, which could restore some bits of the key by analyzing the effect of the particular differences in plaintext pairs on the differences in ciphertext. Although the differential cryptanalysis is proposed to analyze DES which is one of the most effective ways to attack iteration block cipher, it is also an effective cryptanalysis method for other similar ciphers with fixed S boxes. Since the differential cryptanalysis method is proposed, the ability of resisting differential attack is an important indicator to measure the security of block cipher system when a block cipher is designed. In this paper we firstly analyze the differential analysis method, and put forward an algorithm of searching the best differential path for lightweight block cipher with SPN structure. In this algorithm the design of confusion layer and diffusion layer is separated, and the best differential characteristics of each round could be obtained by recursion calculation. Finally, the best differential characteristics of each round couldbe obtained.RECTANGLE lightweight block cipher algorithm is proposed by Wentao Zhang, Zhenzhen Bao and Dongdai Lin in 2014. The algorithm uses SPN structure and 4×4bit S boxes. As the author said, it has low resource consumption and simple hardware implementation. The author use Bit-slice technology on software implementation, so the RECTANGLE algorithm has more advantages in software implementation than other lightweight block ciphers. We have achieved the search algorithm for differential iterative characteristics of RECTANGLE, and get the same result with the writer. At the same time, we change the left shift digit of the second or third line to improve the P Permutation which breaks a group of differential characteristics with higher probability per round in original algorithm, and we choose a new P Permutation under the situation of only one full spread round added which makes the probability of the best differential path higher than before. The improvement of the algorithm is proved to be more effective in defensing the differential attacks.