Supporting secure transcoding in JPSEC

ABSTRACT The capture, processing, delivery, and display or printing of digital images is important today and will become even more important in the future. Important additional future challenges include the remote browsing of images, image adaptation to support diverse clients, and providing security services such as confidentiality and authentication. In this context, an important functionality is secure transcoding : providing end-to-end security between the content creator and the content consumer, while enabling a potentially untrusted mid-network node or proxy to adapt the content to be best matched for delivery to the consumer  where the adaptation is performed without requiring the node or proxy to unprotect (i.e., decrypt) the content. In prior work, secure transcoding was shown to be possible through a framework referred to as Secure Scalable Streaming, which was originally designed for video streaming applications. Secure transcoding was identified as being possible within the ISO/IEC JPEG-2000 Security (JPSEC) standardization effort, and this paper describes how the JPSEC standard was designed to support rate-distortion (R-D) optimized secure transcoding. 1. Introduction Digital imagery is an important application driver today and will become even more so in the future. Future cell phones and PDAs will include built-in multi-megapixel cameras, satellite imagery is becoming available to every consumer (e.g. terraserver.microsoft.com), and digital cinema (e.g. digital distribution and screening of Hollywood movies) is undergoing standardization. Similarly, display devices and printers are increasing in quality and dropping in cost, size, power requirements, etc. Because of these trends, digital imagery is likely to become increasingly important in the future. Along with this importance comes challenges of efficiently compressing, delivering, adapting, and securing these images. The goal of the emerging ISO/IEC JPEG-2000 Security (JPSEC) standardization effort is to provide a standardized framework for the security of digital images [1]. JPSEC required the development of protection tools and a signaling syntax that allows independent and networked components to interoperate with one another. The tools and syntax must be simple to allow for widespread adoption, flexible to satisfy most security needs, efficient to provide high performance, and of course must provide the different security services and levels of security needed by the diverse range of possible applications. In this paper, we describe how the JPSEC standard suppor ts cofidentiality and authentication in a manner that allows secure scalable streaming and secure tran scoding. Specifically, we discuss three elements of the JPSEC design that are important for secure imaging. x Encryption that enables secure transcoding: We define secure transcoding to mean the capability to adapt a protected media object without requiring to unprotect it. For example, secure transcoding enables an encrypted image to be transcoded without requiring decryption. This can also be performed in an R-D optimized manner and the end-user can verify that the adaption was performed in a valid and permissible manner (next). x Distortion field: We defined a distortion field that describes R-D hints that enable intelligent (but content-unaware) processing of an encrypted JPSEC file. These R-D hints include the distortion that would be incurred if a JPSEC segment is not available at the deco der, as well as the tile, resolution, quality level, color component, and precinct (spatial-freq region) attributes associated with different parts of the JPSEC bitstream. These R-D hints enable R-D optimized secure transcoding to be performed  that is R-D optimized transcoding without knowing what the content is. x Authentication: JPSEC supports authentication (digital signatures or MACs) in a manner that allows the JPSEC creator to determine and specify the allowed mo difications, and allows the JPSEC consumer or end-