Selective encryption of the MC-EZBC bitstream and residual information

When selective encryption is used for security in DRM schemes some information of the original bitstream is intentionally left in plain text. This can have various reasons, e.g. generating preview versions for try and buy scenarios. In the case of the MC-EZBC there is also the goal of retaining the scaling capability in the encrypted domain. However, since parts of the bitstream remain in plaintext this information is available to a potential attacker at all times. In this paper we will assess which attacks can be done with this residual information. Consequently we will extend a prior version of selective encryption for the MC-EZBC to include motion vectors.