Cobra-H64/128算法的相关密钥-差分攻击

本文研究了Cobra-H64/128分组密码算法在相关密钥-差分攻击下的安全性.针对Cobra-H64算法,利用新构造的相关密钥-差分路径和CP逆变换存在的信息泄露规律给出攻击算法1,恢复出了全部128bit密钥,相应的计算复杂度为2^40.5次Cobra-H64算法加密,数据复杂度为2^40.5个选择明文,存储复杂度为2^22bit,成功率约为1;针对Cobra-H128算法,利用新构造的相关密钥-差分路径给出攻击算法2,恢复出了全部256bit密钥,相应的计算复杂度为2^76次Cobra-H128算法加密,数据复杂度为2^76个选择明文,存储复杂度为2^16.2bit.分析结果表明,Cobra-H64/128算法在相关密钥-差分攻击条件下是不安全的.

Related-Key Differential Attacks on Cobra-H64/128

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.