Abstract: Using the linear property of the key schedule algorithm, the authors give a related-key attack on 5-round IDEA (the international data encryption algorithm) that has a time complexity of 2^70.5 5-round IDEA encryptions, and then present an improved meet-in-the-middle attack, which on 5-round variant of IDEA only requires 2⁷ chosen plaintexts and 2¹²⁰ 5-round IDEA encryptions.

Key words: block cipher, IDEA, cryptanalysis, related-key

摘要： 利用IDEA密钥扩展算法的线性特点,结合IDEA算法的性质提出了两种对5轮IDEA算法的攻击。第 1 种攻击采用相关密钥的思想,计算复杂度约为2^70.5 次加密5 轮IDEA 算法;第2⁷种攻击利用密钥特点, 攻击5轮仅需要27个选择明文, 计算复杂度约为2¹²⁰ 次加密 5 轮 IDEA 算法。

关键词: 分组密码, IDEA, 密码分析, 相关密钥