Encryption and Authentication for Scalable Multimedia: Current State of the Art and Challenges Bin B. Zhu 1 , Mitchell D. Swanson 2 , Shipeng Li 1 1 Microsoft Research Asia, Beijing, 100080, China 2 General Dynamics Advanced Information Systems, Bloomington, MN 55431, USA ABSTRACT Scalable coding is a technology that encodes a multimedia signal in a scalable manner where various representations can be extracted from a single codestream to fit a wide range of applications. Many new scalable coders such as JPEG 2000 and MPEG-4 FGS offer fine granularity scalability to provide near continuous optimal tradeoff between quality and rates in a large range. This fine granularity scalability poses great new challenges to the design of encryption and authentication systems for scalable media in Digital Rights Management (DRM) and other applications. It may be desirable or even mandatory to maintain a certain level of scalability in the encrypted or signed codestream so that no decryption or re-signing is needed when legitimate adaptations are applied. In other words, the encryption and authentication should be scalable, i.e., adaptation friendly. Otherwise secrets have to be shared with every intermediate stage along the content delivery system which performs adaptation manipulations. Sharing secrets with many parties would jeopardize the overall security of a system since the security depends on the weakest component of the system. In this paper, we first describe general requirements and desirable features for an encryption or authentication system for scalable media, esp. those not encountered with the non-scalable case. Then we present an overview of the current state of the art of technologies in scalable encryption and authentication. These technologies include full and selective encryption schemes that maintain the original or coarser granularity of scalability offered by an unencrypted scalable codestream, layered access control and block level authentication that reduce the fine granularity of scalability to a block level, among others. Finally, we summarize existing challenges and propose future research directions. Keywords: Multimedia encryption, multimedia authentication, selective encryption, scalable encryption, scalable authentication, security, digital rights management, DRM, layered access control, JPEG 2000, MPEG-4 FGS, fine granularity scalability 1. INTRODUCTION Recent advances in wired and wireless communications and increasing hardware capability have led to a phenomenal growth of multimedia applications in our daily lives. Many efforts have been pursued to enable users to access multimedia anywhere, anytime, with any devices. Networks may have different capacities and characteristics. Devices may have different display sizes and computing capabilities. To realize access to multimedia anywhere, anytime, and with any devices, a traditional approach is to compress a single multimedia signal into multiple copies, with each copy targeted at a specific application scenario such as a PC with wideband Internet access, a 3G cellular phone, etc. These multiple copies are all stored in a server to make them available for each individual user to select a copy that best fits his or her need. Another approach is to apply a transcoder at some node of the multimedia delivery path to generate a lower resolution or quality bitstream to fit the targeted network condition or device capability. Both approaches may need to be combined since multiple copies of a multimedia signal can only address a given number of preset client capabilities and network conditions. Author contact information: Bin Zhu (contact author): binzhu@ieee.org, Mitchell D. Swanson: Mitchell.Swanson@gd-ais.com, Shipeng Li: spli@microsoft.com