Information Hiding Algorithms Based On Digital Television Conditional Access System

With the coming of Information Age, especially the spread of computer networkingtechnology, the way people transmit information varies and trends to get more convenientand rapid. However, the protection of much information covered national security, tradesecret, personal privacy, et al, has received more attention, and security problems need to besolved. To ensure data security, the general technique is encryption, whereas it is likely todraw the adversary‘s attention. In addition, the decoding speed becomes faster since thecomputing power of computers is growing. Even if the password is enough strong, there aremany methods to distort or destroy the cipher text. In this case, a branch of informationsecurity technology–the information hiding technology has attracted people‘s attention. Sofar, lots of achievements have been made on the information hiding utilizing multimediaand Internet protocols. However, hiding information based on the digital television systemis rare. Compared with other carriers, digital television has many significant advantages:1.Mass of digital TV signal data provide abundant carriers for information hiding.2. DigitalTV system has prefect infrastructure and wide coverage area for widespread transmission.3.That few intermediate apparatus in digital TV network make hidden message difficult to bechanged. Digital TV Conditional Access (CA) system is used to control the user to receivethe service. Security is the most pressing issue of the CA system.At first, we divide DVB network into four layers according to the research results inInternet covert channels, after that we introduce the conception of hiding information inDigital TV system and analyze the feasibility of hiding information based on DVB network.Then two covert channels based on padding area and the reserved bits of PCR field weredesigned, through analyzing the characteristics of TS packet‘s adaption filed, and theirperformance were evaluated. By an in-depth study on the conditional access system, threekinds of covert channels based on the special field of CA table were proposed according totheir features, They are the covert channels based on reserved bits of CA message header,CA_section_length field of EMM message header and modifying the structure of ECMmessage. And then we evaluated the performance on stealthiness, capacity and robustness.Finally, we accomplished the simulation and capacity analysis of covert channels abovewith C++language. a modified information hiding method was proposed based on the different values in CA_section_length area. Theoretical analysis and experimental resultsshow this method can enhance the channel capacity.