关键词: 密码分析, Cobra-H64/128算法, 相关密钥-差分攻击, 差分传递特性, 比特传递特性

Abstract: The security of Cobra-H64/128 block cipher under related-key differential cryptanalysis was studied.For Cobra-H64,we use related-key differential attack to get the whole 128 bits key with probability 1 based on the new constructed related-key differential and loopholes in CP box,and the corresponding computational complexity is 2^40.5 Cobra-H64 encryptions,the data complexity is 2^40.5 chosen-plaintexts,the memory complexity is 2^22 bits.To recover the whole 256 bits key of Cobra-H128,we need a computational complexity of 2^76 Cobra-H128 encryptions,a data complexity of 2^76 chosen-plaintexts,a memory complexity of 2^16.2 bits.The analysis results show that Cobra-H64/128 are unsafe under related-key differential attacks.

Key words: cryptanalysis, Cobra-H64/128 block cipher, related-key differential attack, differential transmission characteristic, bit transmission property