Security Analysis of Selectively Encrypted MPEG-2 Streams

Selective encryption exploits the relationship between encryption and compression to reduce encryption requirements, saving in complexity and facilitating new system functionality. Selective encryption of MPEG video streams has been proposed in a number of variations, yet has seen little application to date. Here we focus on high encryption savings, targeting 10% of the bit stream or less encrypted, moderate security in the sense that the content is degraded to the point that purchase would be preferred over consuming free content, no impact on compression efficiency, and a cryptanalytic approach to validating security. We find that adequate security is plausible if the compressor is cooperative or at least neutral with respect to the selective encryption system, but implausible if the compressor is operated antagonistically. The unusually low encryption targeted makes application of this solution appealing.