The impact of digital rights management on network security design--Part I

Symmetric encryption is the backbone of security design as it permits high performance encryption and decryption of data with modest overhead. Symmetric encryption requires that identical keys are available at each end of the network and the keys are usually generated by algorithmic methods or distributed through out of band communications.

Cryptographers now equate symmetric algorithms to the Advanced Encryption Standard (AES) as it is the cipher recommended by NIST and is the default candidate for any new security design. There are some venerable ciphers in broad use including the Data Encryption Standard (DES) and RC4 (primarily in SSL) which are used in Microsoft Windows Media DRM for Mobile. The table below outlines the cipher choices selected by the DRM implementers or licensing bodies.

One observation is that DRM system designers often optimize for a specific application. This is certainly the case for HDMI where a proprietary cipher design was developed by the Digital Content Protection, LLC with the goal of implementing a streaming cipher capable of achieving up to 5 Gbps of throughput.

The HDCP cipher encrypts and decrypts uncompressed, high-definition digital video in a low cost format suitable for consumer electronics such as flat panel TVs or high definition DVD players. While the cipher is extremely efficient, the design was broken in a matter of months and remains open to exploits despite its widespread use. There are no shortcuts in good security design and re-inventing the wheel is seldom the right path to follow. Although it has a slightly higher gate count, the licensing authority for HDCP should convert to a NIST approved cipher with GCM-AES being the right choice.

About the Author Al Hawtin is VP Marketing and Business Development at Elliptic Semiconductor. Elliptic develops and licenses security designs for semiconductor intellectual property and middleware for rights management, storage and network applications.

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