Unformatted text preview: left and right halves are equal, or SINGLE which contains only 56 bits. The CCA functions specify hardware enforcement of certain key types to be used for some operations. The CV is checked in a secure hardware processor: It must conform to the permitted CCA rules for each CCA function. If the CV successfully passes the test requirements, a variant of the KEK or MK is obtained by the XOR of the KEK or MK with the CV, and the plaintext target key is recovered for use internally with the CCA function. When new keys are generated, the CV specifies the uses of the generated key. Those combinations of key types that could be used in attacking the system are not generated or imported into a CCA-compliant system. CCA uses a combination of public-key cryptography and secret-key cryptography for key distribution. The KDC shares a secret master key with each user and encrypts session keys using that master key. Master keys are distributed using public-key cryptography. The system’s designers chose this hybrid approach for two reasons. The first is performance. Public-key cryptography is computationally intensive; if session keys are distributed using public-key cryptography, the system might bog down. The second is backwards compatibility; this system can be overlaid on existing secret-key schemes with minimal disruption. CCA systems are designed to be interoperable. For systems that are non-CCA compliant, a Control Vector Translate (CVXLT) function permits keys to be passed between the two implementations. Initialization of the CVXLT function requires dual control. Two individuals must set up the required translation tables independently. Such dual control provides a high degree of assurance concerning the integrity and pedigree of any keys introduced into the system. A key of type DATA is provided for compatibility with other systems. A DATA key is stored with a CV that identifies the key as a DATA key. DATA keys can have broad uses and as such must be regarded with suspicion and used with care. DATA keys may not be used f...
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- Fall '10
- Cryptography, Bruce Schneier, Applied Cryptography, EarthWeb, Search Search Tips