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Cryptanalysis of C2

2009; Springer Science+Business Media; Linguagem: Inglês

10.1007/978-3-642-03356-8_15

1611-3349

Julia Borghoff, Lars R. Knudsen, Gregor Leander, Krystian Matusiewicz,

Coding theory and cryptography

We present several attacks on the block cipher C2, which is used for encrypting DVD Audio discs and Secure Digital cards. C2 has a 56 bit key and a secret 8 to 8 bit S-box. We show that if the attacker is allowed to choose the key, the S-box can be recovered in 224 C2 encryptions. Attacking the 56 bit key for a known S-box can be done in complexity 248. Finally, a C2 implementation with a 8 to 8 bit secret S-box (equivalent to 2048 secret bits) and a 56 bit secret key can be attacked in 253.5 C2 encryptions on average.