Zero-Correlation Linear Cryptanalysis with FFT and Improved Attacks on ISO Standards Camellia and CLEFIA

Zero-correlation linear cryptanalysis is based on the linear approximations with correlation exactly zero, which essentially generalizes the integral property, and has already been applied to several block ciphers -- among others, yielding best known attacks to date on round-reduced TEA and CAST-256 as published in FSE'12 and ASIACRYPT'12, respectively. In this paper, we use the FFT Fast Fourier Transform technique to speed up the zero-correlation cryptanalysis. First, this allows us to improve upon the state-of-the-art cryptanalysis for the ISO/IEC standard and CRYPTREC-portfolio cipher Camellia. Namely, we present zero-correlation attacks on 11-round Camellia-128 and 12-round Camellia-192 with $$FL/FL^{-1}$$ and whitening key starting from the first round, which is an improvement in the number of attacked rounds in both cases. Moreover, we provide multidimensional zero-correlation cryptanalysis of 14-round CLEFIA-192 and 15-round CLEFIA-256 that are attacks on the highest numbers of rounds in the classical single-key setting, respectively, with improvements in memory complexity.