Research On Cryptanalysis Of Block Cipher

As an important part of symmetric-key cryptography, the block cipher is a core component of some cryptology systems. It can provide the information security such as confidentiality and data integrity. The security analysis of block cipher is always a very active branch in cryptanalysis. Therefore, the research on some new cryptanalytic tools brings a far reaching meaning in design and analysis of block cipher.The thesis has a deep research on the impossible differential attack, the multi-trail differential attack, the bit-pattern integral attack and the improved meet-in-the-middle attack. Based on the obtained conclusion in research, we then apply these cryptanalytic tools on block ciphers such as ARIA, AC and CLEFIA. Main contributions of this dissertation are summarized as follows:1. Research on the impossible differential characteristic of a class of SP structure block cipher. A new method is designed to classify the linear diffusion input values by the weight of differential, and the impossible differential characteristics of the SP structure block cipher are analyzed. We specifically construct a new general kind of 6-rond ARIA impossible differential in detail, and prove there are only two classess of impossible differential when the input-and-output weight of differential is ten. The impossible differential structures and count values are also proposed. Finally, we prove there is no 6-round impossible differential with the input-and-output differential weight less than ten based on this new method.2. Research on the multi-trail differential attack of ARIA. We prove there are only two differentials reaching the upper bound of maximal probability. What's more, when it comes to the multi-trial differentials, 2-round recycled multi-trial differential with maximal probability is presented.3. Research on the bit-pattern integral attack. The bit-pattern integral attack is improved with the definition of pattern period. Then we apply the improved bit-pattern integral attack on the AC block cipher, construct 3-round integral distinguisher, and finally analyze the security of 4-round AC against bit-pattern integral attack. With 213.5 chosen plaintexts and 247 4-round AC encryption, we successfully recover 128-bit final round key.4. Research on the improved meet-in-the-middle attack. We analyze the security of 4-branch generalized Feistel structure against the improved meet-in-the-middle attack and concretely take CLEFIA as an application example. Without the key whitening, we construct three classes of distinguishers and successfully attack 10-round CLEFIA-128/192/256, 11-round CLEFIA-192/256 and 12-round CLEFIA-256 respectively. The results show that 10-round CLEFIA-128/192/256, 11-round CLEFIA-192/256 and 12-round CLEFIA-256 are not immune to the improved meet-in-the-middle attack. And compared to the existing cryptanalytic tools for attacking the same round CLEFIA, the improved meet-in-the-middle attack requires the lowest data complexity.