CONDITIONAL ACCESS AND ENCRYPTION OPTIONS FOR DIGITAL COMPRESSION SYSTEMS 1V/COM Intemational 16516 Via Esprillo San Diego, CA 92127 Tony Wechselberger Executive Vice President Abstract Many methodologies have been developed for terrestrial, satellite and The development of digital cable distribution for both broadcast transport of television signals marks a and point-to-point applications. change from traditional approaches for "secure" distribution using analog For entertainment scrambling technology. The aU-digital distribution, true encryption nature of these signals makes hard techniques were introduced in the encryption of aU program services and early 1980's. Since that time there network information possible, and thus has been a steady increase in the our expectations for good security adoption of encryption techniques, performance over long periods of time leading (eventually) to a better in future digital compression systems awareness in, and utility of proper is high. application of cryptographic technology. At the same time there is much effort today to standardize elements Except for very high cost and subsystems of this new systems that could afford total technology, such that maximum digitization of the audio and video benefits accrue from interoperability material, virtually all existing with related developing technologies systems have employed techniques and markets. This paper discusses the that use the "randomizing" issues surrounding encryption in capabilities of encryption to digital compression systems, and deterministically "scramble" analog explores the possibUities for encryption program components, and reorder or standardization in certain areas of the otherwise reassemble these transport level. Included are comments components at the receiving end. on replaceable "Smart Card" and Examples of this are line shuffling, "Processor Card" approaches and cut-and-rotation, and random benefits. inversion of video. The fundamentally analog INTRODUCTION nature of the above randomizing approaches has problems. For The consumer and commercial example, in most implementations business and entertainment (but not all) enough recognizable television industries have now some information remains in the received twenty years of experience in the programming to sometimes not design, fielding and operation of satisfy desired requirements of a privacyI conditional access systems. good conditional access security 1993 NCTA TECHNICAL PAPERS -- 144 system-namely that the scrambled positive and negative reactions information contain no useful throughout the operator /user base. remnants of its original form, and In addition the esoteric nature of that reconstruction of the signal not cryptographic technology, in be possible by examination of the combination with the veil of secrecy scrambled waveform alone. (For a that surrounds most products tends good treatise on desirable attributes to shroud reality from view. The of security systems, see reference [1].) result is that decisions regarding the whole subject become driven in part In addition, the ways in which by sound technical judgments and the need for security systems part by emotion. developed and solutions evolved have resulted in a plethora of different The very mention of systems which are not only "standardized conditional access" in incompatible with each other, but the wrong circles will frequently be also with other types of equipment met by cries of eventual disaster. Yet used at the source, transit, storage many who have studied the issue or display chain. (Most obviously from a neutral position have evidenced by the consumer concluded that when theory and environment situation, and the experience are applied properly, there resultant quagmire of "opportunities" are indeed procedures and structures to be solved there.) that can be implemented to provide some basis of commonality in future Today we find ourselves at the generation systems. Note the many crossroads of a technological digital non-military implementation revolution: one where participation standards used by the U.S. in going forward forces decisions to government and the longevity of the be made that involve significant DES algorithm, for example. departures from previous generation technology. This change begs the The motivation for the examination of opportunities to consideration of standardization attain improvements over the current develops primarily from compatibility situation in several areas, such as and interoperability issues. More and consumer friendliness, compatibility more relationship and and interoperability, improved interdependency exists today between security, ... all topics where some heretofore unrelated markets. This degree of standardization has trend will dramatically expand. The important potential. One of the more merging of the television and controversial areas is computer industries into a standardization of conditional "multimedia environment" is in the access. The all-digital nature of sights of many wishing to put to use compression systems provides at the broadband highways that lie in least the technical opportunity for our future. The growth accomplished future-friendly advances in this area. by these new markets will be throttled by interoperability issues. STANPARDIZATION Surrounding digital compres­ sion developments are significant The experiences of our industry efforts to define standards. Driven with encryption products over the primarily through the International past decade has left a trail of both Standards Organization (ISO), the 1993 NCTA TECHNICAL PAPERS -- 145 global unification of digital television stream will be "packetized"; that is, program generation, editing, storage, consist of packets of data (sizes of retrieval, transport and display is the packets are in the 130 byte to leading to a set of agreed upon 192 byte range) containing digital methodologies for audio and video information from a single elementary compression, and transport of stream or data type. The packets will complex multiplexes of associated each be preceded by a "header" of up data and ancillary digital services. to 4 bytes of packet-specific These standards, known as information such as packet ID, "MPEG-2," cover the primary areas of clearI scrambled indicator, even/ odd audio compression, video key, continuity counter and other compression and transport. They will information. The "generalized" digital serve as the guides to intemational nature of these packets makes for utility of future systems for most very flexible opportunities in the area indus trial and consumer of encryption and conditional access, applications. and the packets can be easily and singularly protected (scrambled) In the transport area, the work throughout their distribution and has led to the development of a routing "life." working draft which defines: In order for the digital • Program Stream-A grouping of television market to fully and freely audio, video and data elemental develop, it is very important not only components having a common that specific audio and video time relationship, and being compression techniques be codified, generally "associated" for delivery, but this transport area as well. The storage, playback, etc. requirements vary greatly between various applications for digital • n-ansport Stream-A collection of storage media (DSM) and direct program streams or elementary broadcast satellite (DBS), for streams (video, audio, data) which example. Yet it is essential that easy have been multiplexed in a non­ movement between such mediums be specific relationship for purposes available. Many factors come into of transmission. play, such as timing, program stream reconstruction, synchronization, While discussions are de I remultiplexing, (re)packetizing, continuing at the time of this and of course the need for encryption writing, these "system layer" efforts in certain applications. are aimed at providing a basic data structure, the "semantics and It has been an objective of the syntax" of a data stream, that can ISO systems working group to limit serve as a common format for local the extent of "specification" to a and broadcast transmission. minimum ... to defme only as much as is generally agreed to provide Entities working within the meaningful interoperability. The ISO MPEG-2 System Layer Group remainder of this paper discusses the have agreed to a number of basic implications of encryption on structural elements that are expected interoperability, and the issues to become part of the system layer regarding separation of systems and syntax. Fundamental to this long term security. structure is that the transport 1993 NCTA TECHNICAL PAPERS -- 146 CONDITIONAL ACCESS video/sound/data service (i.e. RECOMMENDATIONS television program or service) in order to prevent unauthorized Both the European (through reception of the information in a the CCIR) and the North American clear form. The alteration is a (primarily through the ATSC) specific process under the control communities have considered the of the conditional access system issues surrounding conditional (sending end). access standardization, and both have extensive expertise and • Access Control-The function of experience in the subject matter. The the conditional access control at conclusions and recommendations of the sending end is to generate the both groups are very similar [1].(2]; scrambling control signals, and that: the provision of information to enable authorized users to conditional access systems can be