Key schedule algorithms play an important role in modern encryption algorithms, and their security is as crucial as the security of the encryption algorithms themselves. Many studies have been performed on the cryptographic strength evaluation of the encryption algorithms; however, strength evaluation of the key schedule algorithms often obtains less attention that can lead towards the possible loophole in the overall encryption process. In this paper, a criterion is proposed to evaluate the cryptographic strength of the key schedule algorithms. This criterion includes different methods of data generation from subkeys and a suitable set of statistical tests. The statistical tests are used to explore the cryptographic properties such as diffusion, confusion, independence, and randomness in the subkeys generated by the key schedule algorithm. The proposed criterion has been applied to some of the key schedule algorithms of different block ciphers. The results confirm that the proposed criterion can effectively differentiate between strong- and weak-key schedule algorithms.

中文翻译：

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密钥调度算法的密码强度评估

密钥调度算法在现代加密算法中起着重要作用，其安全性与加密算法本身的安全性同样重要。关于加密算法的密码强度评估，已经进行了许多研究。但是，密钥调度算法的强度评估通常会引起较少的关注，这可能导致整个加密过程中可能出现漏洞。本文提出了一种评估密钥调度算法密码强度的准则。此标准包括从子项生成数据的不同方法和一组适当的统计测试。统计测试用于探索由密钥调度算法生成的子密钥中的加密属性，例如扩散，混乱，独立性和随机性。所提出的标准已经应用于不同分组密码的一些关键调度算法。结果证实了所提出的准则可以有效地区分强键和弱键调度算法。