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The Cryptomeria cipher, commonly referred to as C2, is a proprietary block cipher defined and licensed by the 4C Entity. It is the successor to CSS algorithm (used for DVD-Video) and was designed for the CPRM/CPPM Digital Rights Management scheme which are used by DRM-restricted Secure Digital cards and DVD-Audio discs.
[edit] Cipher detailsThe C2 symmetric key algorithm is a 10-round Feistel cipher. Like DES, it has a key size of 56 bits and a block size of 64 bits. The encryption and decryption algorithms are available for peer review, but implementations require the so-called "secret constant", the values of the substitution boxes, which are only available under a license from the 4C Entity. No cryptanalytic attacks on the cipher have been published as of December 2006. [edit] Distributed brute force cracking effortFollowing an announcement by Japanese HDTV broadcasters that they would start broadcasting programs with the copy-once broadcast flag starting with 2004-04-05, a distributed Cryptomeria cipher brute force cracking effort was launched on 2003-12-21. To enforce the broadcast flag, digital video recorders employ CPRM-compatible storage devices, which the project aimed to circumvent. However, the project was ended and declared a failure on 2004-03-08 after searching the entire 56-bit keyspace, failing to turn up a valid key for unknown reasons.[1] [edit] References
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