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Source PDF: /mnt/main/jmc-storage/docs/DVB/ETR 289 Support for use of scrambling and Conditional Access (CA) within digital broadcasting systems.pdf Like all conversions the text below should be fully readable as UTF-8 unicode text. --------------------------------------------------------------- ETSI ETR 289 TECHNICAL October 1996 REPORT Source: EBU/CENELEC/ETSI-JTC Reference: DTR/JTC-DVB-14 ICS: 33.020 Key words: DVB, digital, video, broadcasting, TV, CA, security European Broadcasting Union Union Européenne de Radio-Télévision Digital Video Broadcasting (DVB); Support for use of scrambling and Conditional Access (CA) within digital broadcasting systems ETSI European Telecommunications Standards Institute ETSI Secretariat Postal address: F-06921 Sophia Antipolis CEDEX - FRANCE Office address: 650 Route des Lucioles - Sophia Antipolis - Valbonne - FRANCE X.400: c=fr, a=atlas, p=etsi, s=secretariat - Internet: secretariat@etsi.fr Tel.: +33 4 92 94 42 00 - Fax: +33 4 93 65 47 16 Copyright Notification: No part may be reproduced except as authorized by written permission. The copyright and the foregoing restriction extend to reproduction in all media. © European Telecommunications Standards Institute 1996. © European Broadcasting Union 1996. All rights reserved. Page 2 ETR 289: October 1996 Whilst every care has been taken in the preparation and publication of this document, errors in content, typographical or otherwise, may occur. If you have comments concerning its accuracy, please write to "ETSI Editing and Committee Support Dept." at the address shown on the title page. Page 3 ETR 289: October 1996 Contents Foreword .......................................................................................................................................................5 Introduction....................................................................................................................................................5 1 Scope ..................................................................................................................................................7 2 References ..........................................................................................................................................7 3 Definition and abbreviations ................................................................................................................8 3.1 Definition ..............................................................................................................................8 3.2 Abbreviations .......................................................................................................................8 4 The DVB Scrambling Algorithm ..........................................................................................................9 4.1 The DVB Scrambling Algorithm custodian.........................................................................10 5 Use of the scrambling algorithm in an MPEG-2 environment ...........................................................10 5.1 Scrambling control field .....................................................................................................10 5.2 Registration of CA System ID ............................................................................................10 5.3 PES level scrambling issues..............................................................................................11 6 Trans-control issues when crossing distribution media boundaries..................................................11 7 Conditional Access (CA) data ...........................................................................................................11 History..........................................................................................................................................................13 Page 4 ETR 289: October 1996 Blank page Page 5 ETR 289: October 1996 Foreword This ETSI Technical Report (ETR) has been produced under the authority of the Joint Technical Committee (JTC) of the European Broadcasting Union (EBU), Comité Européen de Normalisation ELECtrotechnique (CENELEC) and the European Telecommunications Standards Institute (ETSI). This ETR may be converted into an ETS after market feedback. For this purpose, the wording of an ETS rather than of an ETR is used. ETRs are informative documents resulting from ETSI studies which are not appropriate for European Telecommunication Standard (ETS) or Interim European Telecommunication Standard (I-ETS) status. An ETR may be used to publish material which is either of an informative nature, relating to the use or the application of ETSs or I-ETSs, or which is immature and not yet suitable for formal adoption as an ETS or an I-ETS. NOTE: The EBU/ETSI JTC was established in 1990 to co-ordinate the drafting of ETSs in the specific field of broadcasting and related fields. Since 1995 the JTC became a tripartite body by including in the Memorandum of Understanding also CENELEC, which is responsible for the standardization of radio and television receivers. The EBU is a professional association of broadcasting organisations whose work includes the co-ordination of its Members' activities in the technical, legal, programme-making and programme-exchange domains. The EBU has Active Members in about 60 countries in the European Broadcasting Area; its headquarters is in Geneva *. * European Broadcasting Union Case Postale 67 CH-1218 GRAND SACONNEX (Geneva) Switzerland Tel: +41 22 717 21 11 Fax: +41 22 717 24 81 Introduction This ETR addresses the addition of Conditional Access (CA) elements to the ISO/IEC 13818-1 (MPEG-2) [1]. The Conditional Access System (CAS) is a very sensitive area, and this ETR describes the minimum set of common CA elements necessary to achieve interoperability between different CA Systems. It is reasonable to expect these common CA elements to be incorporated in every piece of consumer receiver equipment for digital TV. In additional clauses, some CA elements are defined which are not needed from an interoperability point of view, but will enhance commonality in cable TV (CATV) receiver equipment. Page 6 ETR 289: October 1996 Blank page Page 7 ETR 289: October 1996 1 Scope This ETSI Technical Report (ETR) specifies the common DVB Conditional Access elements. It was developed principally to provide support for a wide range of Conditional Access Systems (CASs) which are based on ISO/IEC 13818-1 (MPEG-2) [1] and the DVB specifications. The ETR specifies those aspects which are required for co-existence of multiple Conditional Access Systems in a single data stream. 2 References For the purposes of this ETR, the following references apply: [1] ISO/IEC 13818-1: "Information Technology - Generic coding of moving pictures and associated audio: Systems, Recommendation H.222.0". [2] ISO/IEC 13818-4: "Information Technology - Generic coding of moving pictures and associated audio: Compliance". [3] ETR 162: "Digital broadcasting systems for television, sound and data services; Allocation of Service Information (SI) codes for Digital Video Broadcasting (DVB) systems". [4] ETS 300 468: "Digital Video Broadcasting (DVB); Specification for Service Information (SI) in DVB systems". [5] ETR 211: "Digital broadcasting systems for television; Guidelines on the implementation and usage of Service Information (SI)". [6] ETR 154: "Digital Video Broadcasting (DVB); Implementation guidelines for the use of MPEG-2 Systems, Video and Audio in satellite, cable and terrestrial broadcasting applications". Page 8 ETR 289: October 1996 3 Definition and abbreviations 3.1 Definition For the purposes of this ETR, the following definition applies: Custodian: Distribution authority for the DVB Scrambling Algorithm. 3.2 Abbreviations For the purposes of this ETR, the following abbreviations apply: AF Adaptation Field bslbf bit string, left bit first CA Conditional Access CAS Conditional Access System CATV Community Access TeleVision DVB Digital Video Broadcasting ECM Entitlement Control Message EMM Entitlement Management Messages ID Identifier IEC International Electrotechnical Commission ISO International Organization for Standardization MPEG Moving Picture Experts Group NDA Non-Disclosure Agreement PES Packetized Elementary Stream PID Packet Identifier PMT Program Map Table PSI Program Specific Information SMS Subscriber Management System TS Transport Stream uimsbf unsigned integer, most significant bit first Page 9 ETR 289: October 1996 4 The DVB Scrambling Algorithm The Scrambling Algorithm specified for common DVB applications has been designed to minimise the likelihood of piracy attack over a long period of time and thus contains highly security sensitive information. The technical details of the scrambling algorithm can only be made available to bona-fide users upon signature of a Non-Disclosure Agreement (NDA) administered by a Custodian. This clause contains a summary of the scrambling method and some of the implementation issues. The scrambling algorithm operates on the payload of a Transport Stream (TS) packet in the case of TS-level scrambling. A structuring of PES packets is used to implement PES-level scrambling with the same scrambling algorithm. The PES level scrambling method requires that the PES packet header shall not be scrambled (as required in ISO/IEC 13818-1 [1]) and TS packets containing parts of a scrambled PES packet shall not contain an Adaptation Field (with the exception of the TS packet containing the end of the PES packet). The header of a scrambled PES packet shall not span multiple TS packets. The TS packet carrying the start of a scrambled PES packet is filled by the PES header and the first part of the PES packet payload. In this way, the first part of the PES packet payload is scrambled exactly as a TS packet with a similar size payload. The remaining part of the PES packet payload is split in super-blocks of 184 bytes. Each super- block is scrambled exactly as a TS packet payload of 184 bytes. The end of the PES packet payload is aligned with the end of the TS packet (as required in ISO/IEC 13818-1 [1]) by inserting an Adaptation Field of suitable size. If the length of the PES packet is not a multiple of 184 bytes, the last part of the PES packet payload (from 1 to 183 bytes) is scrambled exactly as a TS packet with a similar size payload. A schematic diagram describing the mapping of scrambled PES packets into TS packets is given in figure 1. Figure 1: PES level scrambling diagram The PES level scrambling method puts some constraints on the multiplexing process in order to make the de-scrambling process easier. Subclause 5.3 gives recommendations for the mapping of scrambled PES packets into TS packets. This method may create some bit-rate overhead if Adaptation Fields (AFs) are needed in TS packets carrying scrambled PES packets. In that case a TS packet containing only an Adaptation Field needs to be inserted. For applications that scramble MPEG-2 Sections, a problem occurs as the MPEG-2 specified syntax does not include any scrambling control bits. Therefore, the scrambling of Sections shall be at the TS level and shall be signalled by the scrambling control field bits. Clear and scrambled Sections cannot be combined in a single TS packet. The MPEG-2 defined padding mechanism can be used to create TS packets with only clear or only scrambled Sections. This means that the end of a TS packet carrying a Section shall be filled with bytes having a value of 0xFF, in order to separate clear and scrambled Sections into different TS packets. The algorithm is designed to minimise the amount of memory in the de-scrambler circuit at the expense of the complexity in the scrambler. The exact amount of memory and the de-scrambling delay depend on actual implementations. Page 10 ETR 289: October 1996 4.1 The DVB Scrambling Algorithm custodian The Scrambling Algorithm for DVB applications is made available by the Custodian upon signature of a Non-Disclosure Agreement and provided potential users are bone fide. The Custodian is ETSI itself and for information can be obtained by contacting: European Telecommunications Standards Institute (ETSI) Administration Department F-06921 Sophia Antipolis Cedex FRANCE Tel.: +33 4 92 94 42 00 Fax: +33 4 93 65 47 16 5 Use of the scrambling algorithm in an MPEG-2 environment This clause contains syntactical definitions and some operational recommendations for MPEG-2 bitstreams allowing efficient use of the common scrambling algorithm. 5.1 Scrambling control field The MPEG-2 Systems specification contains a scrambling control field of two bits, both in the TS packet header and in the PES packet header. The meaning of these two bits is only partially defined in MPEG-2 , as only one value is defined. Table 1 gives a full definition of the scrambling control bits in the TS packet header. Table 1: Transport_scrambling_control values Bit values Description 00 No scrambling of TS packet payload (MPEG-2 compliant) 01 Reserved for future DVB use 10 TS packet scrambled with Even Key 11 TS packet scrambled with Odd Key The first scrambling control bit now indicates whether or not the payload is scrambled. The second bit indicates the use of Even or Odd Key. If the TS packet payload is not scrambled at the TS level, scrambling of data still might be defined at the PES level. Table 2 defines the scrambling control bits in the PES packet header which are similar to those at the TS level. Similarity in the scrambling control bits and in the scrambling methods for both levels, allow efficient descrambler implementations to be realised. Table 2: PES_scrambling_control values Bit values Description 00 No scrambling of PES packet payload (MPEG-2 compliant) 01 Reserved for future DVB use 10 PES packet scrambled with Even Key 11 PES packet scrambled with Odd Key 5.2 Registration of CA System ID Some registration needs to take place on the CA_System_ID field in the MPEG-2 CA_descriptor() to indicate the various CA Systems Specifiers. The CA_System_ID field allows easy filtering of relevant CA information for a particular Digital TV receiver. ETR 162 [3] specifies a range of 256 values (8-bit) for each of the CA System Specifiers. ETSI, as Custodian, co-ordinates the allocation of new CA System Specifiers to acquire an unique range of CA_System_ID values for their private use. Typical usage of the private 8 bits assigned to each CA System Specifier is for purposes such as version indication and/or for differentiation between different SMS providers using the same CA System. The registration procedures shall adopt the information given in ETR 162 [3]. Page 11 ETR 289: October 1996 5.3 PES level scrambling issues Maximum flexibility in the operation of a broadcast infrastructure requires scrambling to be allowed at the PES level. In order to avoid complex implementations at the consumer receiving equipment, only a single de-scrambling circuit shall be required. Some additional constraints are defined in this subclause in order to achieve PES level scrambling with a limited implementation overhead. These recommendations clearly do not apply to unscrambled PES packets or in the case of TS-level scrambling. Recommendation 1: Scrambling shall only occur at one level (TS or PES) and is not allowed to occur at both levels simultaneously. Recommendation 2: The header of a scrambled PES packet shall not exceed 184 bytes. Recommendation 3: The TS packets carrying parts of a scrambled PES packet, shall not have Adaptation fields with the exception of TS packets containing the end of a PES packet. The TS packet carrying the end of a scrambled PES packet, may carry an Adaptation Field to align of the end of the PES packet with the end of the TS packet. 6 Trans-control issues when crossing distribution media boundaries The Program Specific Information (PSI) part of the MPEG-2 specification contains syntactical elements defining where to find CA system information. The CA table and the Program Map Table (PMT) contain CA descriptors which has a CA_PID field to reference PID values of TS packets that are used to carry CA information such as EMMs and ECMs. It may be desirable to replace (part of) the CA information in these TS packets with other CA data at broadcast distribution media boundary. The following constraints make it possible to have a flexible replacement of the TS packets which carry CA information. Recommendation 4: All TS packets with PID values which are equal to a CA_PID value given in a CA_descriptor of the MPEG-2 specification, shall only contain CA System information. No CA information shall be carried in any other place (e.g. Adaptation Fields). Recommendation 5: Two different CA suppliers shall not have common CA_PID values in the same TS. These recommendations are sufficient to allow efficient trans-control to occur at broadcast delivery media boundary by filtering out CA data and replacing it with new CA information. 7 Conditional Access (CA) data This clause specifies a section mechanism as defined in the ISO/IEC 13818-1 [1] for the transport of Conditional Access (CA) information, such as ECMs, EMMs and future entitlement data. The structure of this CA information is specific to each CA System Specifier. Two types of tables are identified by two different table_id values (see table 4), which are intended for the transmission of ECMs. The header of the CA_message_section() may be used for filtering. The ISO/IEC 13818-1 [1] describes how sections are carried in TS packets. CA_message_sections shall be treated as ISO/IEC 13818-1 [1] private_sections, when inserting them into a TS. The CA message sections specified in table 3 shall have a maximum length of 256 bytes. Page 12 ETR 289: October 1996 Table 3: Syntax for the CA Message Table (CMT) Syntax No. of bits Identifier CA_message_section() { table_id 8 uimsbf section_syntax_indicator 1 bslbf DVB_reserved 1 bslbf ISO_reserved 2 bslbf CA_section_length 12 uimsbf for(i=0; I