Research On Authentication And Key Management Techniques In Digital Content Protection Systems

With the rapid development of network and digital technology, digital contents play a more and more important role in our daily working, learning and living. Digital contents are commonly copyrighted, the holders sell them and expect to win the maximal economic interest. However, while the digitalization feature of digital content allows for efficient storage, transmission and process for legal users, it also results in a shortcut for piracy. How to protect the copyrights of digital content through technological means has become an active research field for industrial and academic community. This paper focuses mainly on the problems of authentication, key management and revocation in digital audio and video content protection systems. Several new methods and schemes are proposed to improve the performance of digital content protection systems by deeply analyzing the techniques, specifications and systems available. The major contributions of this paper are summarized as follows:1. A digital rights management system suitable for IPTV is designed to protect the H.264 contents from piracy in video-on-demand and download service. Some key modules of the system such as H.264 video encryption and decryption, license acquisition and operation at client side are presented.2. A forgery attack on a self-certified signature scheme is presented. An improved scheme with the same security features of Schnorr signature is proposed to resist this kind of attack. If used in digital content protection systems, our scheme can greatly reduce the computational complexity of both parties executing a public-key authentication protocol. A self-certified signature with message recovery is proposed on the basis of the improved self-certified signature.3. An efficient scheme for identity authentication and private key distribution in identity-based cryptosystem is proposed by using the concept of public-key certificate in traditional PKI. In the scheme, a trusted third party is employed to transfer trust and an additional public key is used to set up the secure channel for transmitting the private key. Not only is the number of authentication needed decreased significantly, but the private key distribution problem which had never been dealt with in the original scheme and relating applications is addressed in the new scheme. Based on IBE, we propose an encryption scheme which has one public key with two corresponding private keys. Both of the private keys can be used for decryption, one of which is escrowed to a trustedthird party, the other for non-repudiation signature.4. Based on the secure smartcard assumption under which both attackers and card holder are not able to obtain the private and group key stored in it, a system for multicast content protection and payment is designed by making use of identity-based encryption and identity-based signature schemes. This system can guarantee the secrecy of content transmission with other features like anonymity for payments and simplicity for identification, content authentication and key management.5. A comparison between CVT and CRL in respect of computation time, storage requirement, and communication complexity shows that both of them have the same performance as a whole. An extended scheme of CVT is proposed which inherits most of the advantages of CVT and CRL. The extended scheme gains the advantage of minimal cost of computation and communication at the expense of more storage requirement of the signer.6. After introducing and analyzing the certificate revocation mechanism of some digital content protection systems available, we point out their factors of insecurity. We then propose a universal model for dealing with certificate revocation problem to overcome these deficiencies. This model takes the security of every links in the content protection chain into account. Based on the one-way authentication across the cascading devices in the direction of content flowing, this universal model ensures that the system revocation messages can be processed and spread accurately.7. There is a predictable imperfection and high demand on the device memory capacity when current content protection systems are used to solve the certificate revocation problem. A scheme that needs lower memory and has the ability to deal with revocation information perfectively is proposed based on the universal model. In this scheme, only the serial numbers of local legal devices and illegal devices need to be recorded by limiting the total number of other devices linked with the main device to a constant. Although the capacity needed decreases to a smaller, it is enough for the system to treat with system revocation messages perfectively without increasing computational cost.