1 Type of Question

Task-oriented Question that should eventually result in a Recommendation.

2 Motivation

Studies are currently under way in several countries, on ways to improve the security of conditional access systems used for subscription, pay-per-view and similar services distributed to the home by cable television. The need for such studies immediately emerges when the security and viability of conditional access systems currently used in Europe, the United States and elsewhere is assessed.

Such an assessment shows the evident need to develop new, more performing, pirate-proof systems that would enable a cable television system to implement programme distribution to the home (be it a subscription or a pay-per-view service) with a security level adequate to make it commercially viable. Indeed, conditional access systems that were considered to be totally secure when they were developed only a few years ago for television distribution to the home, have been invariably "compromised" by pirates, who extract the conditional access enabling information and sell it at a fraction of the regular subscription fee.

Any conditional access system can be expected to eventually be compromised, irrespective of its sophistication, if the compromised enabling information can be sold to a sufficiently large base of customers.

It seems that a conditional access system will be more secure if the conditions below are met:

• the scrambling process is highly secure;
• the cryptographic algorithm is highly secure;
• the key and the entitlement information are changed at frequent intervals;
• subscribers are divided into small sub-entities, each with its own key and entitlement.

The concurrence of these conditions makes it expensive to compromise the system, and it reduces the pirate's customer base, to the point where piracy is no longer financially viable.

Another very important aspect that is related to conditional access is the provision of measures to prevent a distributed programme from being copied, unless the owner of its intellectual property rights authorizes such copying. Two approaches, which are not mutually exclusive, are being investigated to achieve this goal:

• The conditional access system could be designed in such a way as to separate viewing authorization from copying authorization. In other words it would provide a viewable output to those users that are authorized to view the programme, but it would provide a recordable output only to those users that are separately authorized to copy it. The issue is further complicated by the need of intellectual property holders to have various degrees of authorization, namely: no copy, one copy or any number of copies.
• The programme could be "watermarked" with a hidden coded information, which can neither be removed nor altered, and would identify the holder to the programme intellectual property rights, thus allowing to trace the history of unauthorized copies and take appropriate legal action against pirates.

The study should thus focus on the following lines:

• the specification of a highly secure scrambling system;
• the specification of a highly secure cryptographic system that can be implemented at a viable cost for cable television distribution to the home, namely, in a mass-produced consumer equipment environment;
• the specification of a key and an enabling information distribution system that has adequate capacity and flexibility to serve the diversified requirements of various cable television systems and their various subscribers;
• the development of a set of guidelines on the optimal time interval at which the key and the enabling information should be updated, and on the optimal size of the subscriber population to which the same enabling information is assigned;
• the specifications for an application of the cryptographic system appropriate to implement copy protection at various levels of authorization (no copy, one copy only, any number of copies);
• the specifications for a highly secure watermarking system that would not affect the quality of the distributed programme.

3 Questions

• What scrambling approaches can be recommended for digital cable television distribution to the home?
• What is the capacity required of a conditional access system for cable television distribution to the home, in terms of number of individually addressable subscribers or subscriber groups, etc.?
• What are the specifications for a (preferably unique) cryptographic approach appropriate to such conditional access system?
• What are the specifications for an application of the cryptographic system, appropriate to implement copy protection at various levels of authorization (no copy, one copy only, any number of copies)?
• What are the specifications for the (preferably unique) removable (e.g. ISO-7816, PCMCIA, etc.) cryptographic device (e.g. smart card), if one is used in such a conditional access system?
• How often should the conditional access key be updated?
• Which criteria should be used to time the replacement of the (removable) cryptographic device or of the enabling information in it?
• What is the optimal size of the subscriber population to which the same key and enabling information may be safely assigned?
• Can conditional access solutions developed for terrestrial and satellite broadcasting be used for cable television also?
• What are the specifications for a highly secure watermarking system that would not affect the quality of the distributed programme?

4 Expected results and anticipated target dates

Depending on the contributions that will be received, and on progress in the preparatory activity of the Rapporteur, the studies will likely result in the preparation of draft new Recommendations by 2003, providing specifications and recommended operating practices.

5 Relationships

Exchange of information with ITU-R Study Group 6 would be useful, to take into account possible parallel studies of Study Group 6. However, it is not clear at this moment whether it would be desirable, or indeed possible to develop a conditional access system, capable simultaneously and optimally to meet the different requirements of cable television and of broadcast television.