A Survey of H.264 AVC/SVC Encryption

13as it is the current state-of-the-art can hardly be consideredsatisfactory in a scientific context. Thus further research shouldfocus on the development of objective metrics for the assessmentof the security of video encryption schemes for thedifferent security and application scenarios. A prerequisite forthe development of novel objective quality / security metricsare subjective tests, in which the actually perceived quality andintelligibility is determined by human observers. Contributionsto this line of research have already been made for transparentJPEG2000 encryption [58]. Objective assessment on the basisof face recognition rates has been proposed for the analysisof privacy preserving encryption [14]. For the assessmentof video encryption schemes in the application scenarios oftransparent encryption and sufficient encryption state-of-theartobjective quality metrics may be suited (however, this hasto be backed up by empirical evidence, i.e., subjective qualityevaluation tests [58]). For content confidentiality, however,novel intelligibility metrics as well as an evaluation frameworkfor these metrics are needed (again subjective tests will haveto be an integral part).Further efforts in the area of H.264 encryption should alsoconsider the standardization of security tools within H.264.Bitstream-oriented encryption, as well as other security features,such as authentication / message integrity and scalableauthentication / message integrity, could be optimally integratedinto the existing H.264 framework, as due to the welldesignedNAL abstraction a backwards-compatible integrationwould be possible. This can be done by using previouslyreserved NAL unit types for signalling security related data,such as encrypted NAL units. The security extension couldeven be implemented without the definition of a novel fileformat, as has been necessary in JPEG2000 [26], i.e., thesecured H.264 bitstreams could be completely backwardscompatible to current H.264 bitstreams.VII. CONCLUSIONIn this survey we have presented, evaluated and discussedvideo encryption schemes for H.264. The choice of a videoencryption scheme depends on the application-context, whatare the security threats in this scenario and which functionalityof the bitstream and video data has to be preserved inthe encrypted domain. 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