«ICS: 33.020 Key words: Digital, video, broadcasting, DVB, TV, CA, security Union Européenne de Radio-Télévision European Broadcasting Union ...»
ETSI ETR 289
TECHNICAL October 1996
Source: EBU/CENELEC/ETSI-JTC Reference: DTR/JTC-DVB-14
Key words: Digital, video, broadcasting, DVB, TV, CA, security
Union Européenne de Radio-Télévision
European Broadcasting Union
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: email@example.com 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
3 Definition and abbreviations
4 The DVB Scrambling Algorithm
4.1 The DVB Scrambling Algorithm custodian
5 Use of the scrambling algorithm in an MPEG-2 environment
5.1 Scrambling control field
5.2 Registration of CA System ID
5.3 PES level scrambling issues
6 Trans-control issues when crossing distribution media boundaries
7 Conditional Access (CA) data
Page 4 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.
Introduction This ETR addresses the addition of Conditional Access (CA) elements to the ISO/IEC 13818-1 (MPEG-2) . 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)  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.
For the purposes of this ETR, the following references apply:
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 ) 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 superblock 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 ) 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.
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.
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.
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.
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  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  describes how sections are carried in TS packets. CA_message_sections shall be treated as ISO/IEC 13818-1  private_sections, when inserting them into a TS.
The CA message sections specified in table 3 shall have a maximum length of 256 bytes.
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section_syntax_indicator: This is a 1-bit indicator which shall always be set to "0".
DVB_reserved: This term indicates that the field may be used in the future for DVB applications and therefore shall not be used for private applications.
ISO_reserved: The term "ISO_reserved" indicates that the value may be used in the future for ISO defined extensions and therefore is not be specified by DVB.
CA_section_length: A 12-bit field. It specifies the number of bytes that follow the section_length field up to the end of the section.
CA_data_byte: This is an 8-bit field which carries private CA information. Up to the first 17 CA_data_bytes may be used for address filtering.
ISBN 2-7437-1032-2 Dépôt légal : Octobre 1996