Abstract
This paper presents a linear cryptanalysis for reduced round variants of CAST-128 and CAST-256 block ciphers. Compared with the linear relation of round function with the bias 2− 17 by J. Nakahara et al., we found the more heavily biased linear approximations for 3 round functions and the highest one is 2− 12.91. We can mount the known-plaintext attack on 6-round CAST-128 and the ciphertext-only attack on 4-round CAST-128. Moreover the known-plaintext attack on 24-round CAST-256 with key size 192 and 256 bits has been given, and the ciphertext-only attack on 21-round CAST-256 with key size 192 and 256 bits can be performed. At the same time, we also present the attack on 18-round CAST-256 with key size 128 bits.
Supported by 973 Program No. 2007CB807902, National Natural Science Foundation of China Key Project No. 90604036, National Outstanding Young Scientist No. 60525201.
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Wang, M., Wang, X., Hu, C. (2009). New Linear Cryptanalytic Results of Reduced-Round of CAST-128 and CAST-256. In: Avanzi, R.M., Keliher, L., Sica, F. (eds) Selected Areas in Cryptography. SAC 2008. Lecture Notes in Computer Science, vol 5381. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-04159-4_28
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DOI: https://doi.org/10.1007/978-3-642-04159-4_28
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