On the provably secure CEW based on orthogonal decomposition

• We propose a provably secure CEWod scheme for multimedia content protection.
• CEWod offers a seamless fusion of encryption and watermarking.
• CEWod has enough flexibility to select suitable encryption and watermarking algorithms.
• The security analysis of CEWod validates its security.
• Experimental results prove that CEWod has better feasibility and robustness.

Commutative Encryption and Watermarking (CEW) combines encryption and watermarking to protect confidentiality and ownership. CEW based on Orthogonal Decomposition (CEWod) has been recommended as a mechanism to implement CEW. CEWod has great potential for multimedia content protection applications if its security is validated. This study investigates the security issues of CEWod and their resolution. By redefining the encryption and watermarking operations and performing security analyses, it is proven that the security of the CEWod scheme is based on the security of the orthogonal transformational matrix, B, as well as on its sub-matrixes, R and S. Applying the principle of computational security in cryptography, the security of B, R and S can be assured by selecting appropriate parameters. With respect to the security requirements used in the existing multimedia content protection solutions, other issues that arise from the CEWod approach are addressed. Experimental results and analysis show the feasibility and robustness of CEWod. This study provides evidences that CEWod can provide the promising solution for a buyer–seller protocol-based security system. The discussion also shows that CEWod can be used to build multi-watermarking systems or re-encryption watermarking combined systems. The latter is very useful for cloud computing security.