分组密码算法CTC的立方分析

Cube Cryptanalysis of Block Cipher CTC

立方攻击是在2009年欧洲密码年会上由Dinur和Shamir提出的一种新型密码分析方法，该方法旨在寻找密钥比特之间的线性关系。CTC（CourtoisToyCipher）是N．Courtois设计的一种用于密码分析研究的分组密码算法，该算法的密钥长度、明文长度和迭代轮数都是可变的。文中利用立方攻击方法针对密钥长度为60bit的4轮CTC进行了分析，在选择明文攻击条件下，结合二次测试可恢复全部密钥，密钥恢复阶段仅需要不到2^10次加密算法。

The cube attack is proposed introduced by Dinur and Shamir as a new cryptanalysis method at EUROCRYPT 2009, it aims to find linear relations among between the key bits. The CTC algorithm, as a block cipher designed by N. Courtois for cryptanalysis research, has scalable number of rounds, block size and key size. The cube attack is applied to the four-round CTC with 60-bit key. By combining quadraticity tests with cube attack, the full secret key bits could be acquired. In key recovery phase, less than 2^10 times of evaluations for CTC cipher are required.