Robust Encryption Schemes for 3D Content Protection

SINCE the 1970s, a large number of encryption schemes have been proposed, among which some have been standardised and widely adopted all over the world, such as data encryption standard (DES) and advanced encryption standard (AES). However, due to the special features of three-dimensional (3D) content, these encryption standards are not a suitable solution for 3D applications. The problem of 3D content encryption is beyond the application of established and well-known encryption algorithms. This is primarily due to the structure of 3D content and the way it is used commercially. Unlike data encryption, where a complete bitstream is encrypted, 3D content encryption introduces several challenges. One of the greatest challenges of 3D content encryption is that, in comparison with traditional data and 2D images, 3D content implies a higher level representation or semantics, and in many 3D applications, it is necessary to maintain 3D semantics, such as the spatial and dimensional stability. The major aim of this thesis is to investigate innovative solutions for encrypting 3D content which ensures the usability of encrypted content through maintaining the spatial and dimensional semantics. To this end, we overviewed the relevant background of 3D content and data encryption. We also investigated the limitations of the current techniques in addressing the challenges of 3D content encryption. The literature review delineated the scope of the research and identified the existing problems and limitations. The important research problems in the field of 3D content encryption are summarised as follows: i) the current encryption technology is not able to preserve the dimensional and spatial stability of 3D content; ii) the correlation between the texture image information and 3D surface geometry discloses the hidden geometry of protected 3D objects; iii) direct application of encryption algorithms to 3D content requires high computational power and introduces delay in real-time communication; and iv) there are no design principles for the construction of secure cryptographic primitives for 3D content, that is, those which are resistant to well-known attacks such as surface reconstruction attacks. To solve these research problems, we investigated several existing 2D and 3D encryption schemes in which we found several security flaws. These cryptanalyses helped us in designing resistant ciphers against well-known attacks. In addition, as efficiency is an important concern in 3D applications, we investigated efficient and fast primitives for 3D content encryption. We established a new mathematical notion which ensures the usability of encrypted 3D content in 3D applications by maintaining the dimensional and spatial stability of encrypted 3D content. We proposed the first solution, which is both theoretically and practically important, for the design and evaluation of an appropriate 3D content encryption scheme. Theoretical and experimental analyses demonstrated the effectiveness of our design principles. The design approach is convincingly supported by a number of new cryptanalytic results. Furthermore, the results of our rigorous cryptanalysis can be used in the future design and analysis of complex encryption schemes for multimedia applications.