Cryptomeria cipher

Cryptomeria cipher

The Feistel function of the Cryptomeria cipher algorithm.
General
Designers	4C Entity
First published	2003
Derived from	DES
Related to	CSS
Cipher detail
Key sizes	56 bits
Block sizes	64 bits
Structure	Feistel network
Rounds	10

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.

Cipher details

The 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.

Distributed brute force cracking effort

Following 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. Because the attack was based on S-box values from DVD-Audio, it was suggested that CPRM may use different S-boxes.

References

Citations covering the entire article

• "C2 Block Cipher Specification" (PDF). 1.0. 4C Entity, LLC. January 17 2003. Retrieved 2009-02-13. {{cite journal}}: Check date values in: |date= (help); Cite journal requires |journal= (help)
• "Software Obfuscation from Crackers' Viewpoint" (PDF). Proceedings of the IASTED International Conference. Puerto Vallarta, Mexico. January 23 2006. Retrieved 2006-08-13. {{cite conference}}: Check date values in: |date= (help); Unknown parameter |booktitle= ignored (|book-title= suggested) (help)