White-Box Cryptography - the Key to Bulletproof Windows Vista DRM

White-box cryptography is the key to bulletproofing Windows Vista digital rights management technology. DRM designates a content protection scheme designed to restrict the usage of digital media. The Windows Media DRM is the term associated with the Windows Vista Content Protection Infrastructure. Microsoft revealed that the decision of including DRM into their latest operating system is a direct result of the necessity to ensure that commercial audiovisual content can be played inside the operating system.

In the context of the evolution of the software implementation of DRM, the inherent cryptography associated with content protection has moved from black-box attack models to white-box attack models. "The traditional threat models used for cryptographic applications are all black-box attack models. In this type of model, an attacker is assumed to have control over almost everything to do with the encryption; only the secret key and the details of the code’s execution are unknown. With software implementations of DRM, this is not the most appropriate threat model," revealed Nick Sullivan, Symantec Security Response Researcher.

DRM cryptography automatically implies a decryption key. Compromising a DRM scheme is equivalent to gaining access to the decryption key. Content protection systems such as CSS and AACS (a platform also included in Vista) have been already breached. And with full access to Vista along with a plethora of disassembly and debugging programs, DRM is no longer an impassible limitation. This type of scenario justifies a white-box attack model.

"In this model, the attacker has full visibility into the software implementation and control over the execution environment. Under such conditions, storing the private key in memory is not a secure option because the attacker has access to the entire system during execution. The most common approach is to integrate the key into the encryption algorithm so that the algorithm performs the encryption properly but the key is never made explicit. None of the new techniques have been proven to be secure; however, their initial successes indicate that it may be possible to achieve the seemingly impossible feat of performing an encryption in full view of an attacker without ever revealing the key," Sullivan added.

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