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The Content Scrambling System (CSS)

The Content Scrambling System (CSS). Carlos Garcia Jurado Suarez 03/10/2006. What is CSS?. CSS is the mechanism for encrypting data on DVDs. Created and administered by the DVD Copy Protection Association around 1996.

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The Content Scrambling System (CSS)

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  1. The Content Scrambling System (CSS) Carlos Garcia Jurado Suarez 03/10/2006

  2. What is CSS? • CSS is the mechanism for encrypting data on DVDs. • Created and administered by the DVD Copy Protection Association around 1996. • The need: DVDs contain digital and high quality versions of movies so perfect copies can be made if the data is not protected. • CSS is not very effective.

  3. CSS basics • Each DVD has a main disk key, which is encrypted with 409 keys (the keys are owned by the CCA). • DVD players have a subset of keys embedded in them (licensed from the CCA) • The players use one of these keys to decrypt the disk key. The decryption is validated against a hash of the decrypted key that is included in the disk.

  4. The CSS Cipher

  5. Why did CSS fail? • Weak cipher. The CSS encryption primitive uses a 40 bit key and is based on LFSRs (a 216 attack is possible). • Software DVD players. These have to ship keys in software so they are easily obtainable. Decrypted data is present in memory at some point. • No revocation mechanism.

  6. DeCSS • Software created by three Norwegian programmers than can rip most DVDs to a hard drive. • Was created be reverse engineering the Xing player (by Real Networks). • Widely available online.

  7. What’s next? • At this time all 409 keys are public. • New standard being developed: AACS (Advanced Access Content System). • Based on AES. • Watermarking for detection of illegal copies • NNL/Media Key Blocks for key management and revocation.

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