Key-assignment strategies for CPPM

ABSTRACT

CSS, the first system to protect multimedia content on the new DVD medium failed badly, because both its encryption algorithm and its key management could easily be broken. A new industry initiative, the 4C Entity, LLC (founded by IBM, Intel, Matsushita and Toshiba), presents a more mature approach, called "Copy Protection for Prerecorded Media" (CPPM), which has already been adopted in DVD-Audio.A key-feature of CPPM is its advanced key-management, which allows for system renewability by revoking compromised devices. Renewability means that content provider can encrypt the content, such that compromised devices cannot decrypt it, whereas non-compromised devices still can.In this paper, we review the basic concepts of CPPM and propose a framework to study its cryptographic strengths based on the published specifications. We will focus our assessment especially on CPPM's key-management scheme, which, unfortunately, is not completely specified in the official publicly available specification. As a consequence, it is currently unknown, how the 4C Entity selects the device keys that are assigned to devices. As a main contribution we propose several suitable key-assignment strategies based on finite geometric structures and study their security.

REFERENCES

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INDEX TERMS

Primary Classification:
  D. Software
  D.4 OPERATING SYSTEMS
      D.4.6 Security and Protection
          Subjects: Access controls

Additional Classification:
  D. Software
  D.4 OPERATING SYSTEMS
      D.4.6 Security and Protection
          Subjects: Cryptographic controls

  K. Computing Milieux
  K.4 COMPUTERS AND SOCIETY
      K.4.4 Electronic Commerce
          Subjects: Intellectual property
  K.6 MANAGEMENT OF COMPUTING AND INFORMATION SYSTEMS
      K.6.5 Security and Protection (D.4.6, K.4.2)

General Terms:
Algorithms, Security, Standardization, Theory

Keywords:
CPPM, content protection, device revocation, key-assignment, key-management