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Definition
C2 is a 64-bit block cipher developed by 4C Entity. It has a 56-bit key and a secret S-box mapping on eight bits.
Background
C2 is the short name for Cryptomeria, a proprietary block cipher defined and licensed by the 4C Entity (a consortium consisting of IBM, Intel, Matsushita and Toshiba) [3]. According to Wikipedia, “It (...) was designed for the CPRM/CPPM Digital Rights Management scheme which is used by DRM-restricted Secure Digital cards and DVD-Audio discs.” [4]. 4C Entity has published a specification of C2 in [2].
Theory
C2 is a 10-round Feistel cipher with 64-bit blocks and 56-bit keys. The S-box is secret and available under license from the 4C Entity. Therefore, one might consider the S-box as part of the secret key. A CPRM compliant device is given a set of secret device keys when manufactured. These keys are used to decrypt certain data of the media to be protected, in order to derive the media keys which have been used in the...
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Recommended Reading
Borghoff J, Knudsen LR, Leander G, Matusiewicz K (2009) Cryptanalysis of C2. In: Halevi S (ed) Advances in cryptology – CRYPTO 2009. Lecture notes in computer science, vol 5677. Springer, Berlin, pp 250–266
C2 Block Cipher Specification, Revision 1.0.http://www.4Centity.com, 2003. Used to be available online from 4C Entity, can be downloaded e.g. from: http://edipermadi.files.wordpress.com/2008/08/cryptomeria-c2-spec.pdf. Accessed 14 Mar 2011
4C Entity, Wikipedia article. http://en.wikipedia.org/wiki/4C_Entity. Accessed 11 Feb 2009
Cryptomeria cipher, Wikipedia article. http://en.wikipedia.org/wiki/Cryptomeria_cipher. Accessed 11 Feb 2009
4C Entity, C2 facsimile s-box. http://www.4centity.com/docs/C2_Facsimile_S-Box.txt. Accessed 14 Mar 2011
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Knudsen, L.R., Leander, G. (2011). C2 – Block Cipher. In: van Tilborg, H.C.A., Jajodia, S. (eds) Encyclopedia of Cryptography and Security. Springer, Boston, MA. https://doi.org/10.1007/978-1-4419-5906-5_552
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DOI: https://doi.org/10.1007/978-1-4419-5906-5_552
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