CD/DVD Copy Protection Tim G¨uneysu 02/12/2004 Advanced Seminar for ITS Ruhr-Universit¨at Bochum Chair for Communication Security Advisor: Andre´ Weimerskirch Contents 1. Introduction 1 2. Specifying the Medium 2 2.1.CharacteristicsofanOpticalDataMedium............. 2 2.2.CDSpecifications........................... 3 2.2.1.RedBook........................... 4 2.2.2.YellowBook.......................... 4 2.3.DVDSpecifications.......................... 5 2.3.1.DVD-ROM.......................... 6 2.3.2.DVD-Video.......................... 6 3. Copy Protection in Theory 8 3.1.TargetApplicationsandBusinessAreas............... 8 3.2.ClassificationofProtections..................... 8 3.2.1.AbusingtheMediumSpecification............. 9 3.2.2.InjectingReadErrorsIntentionally............. 10 3.2.3.VerificationoftheOriginal.................. 10 3.2.4.DigitalSignaturesandCryptography............ 10 4. Protection Implementations 11 4.1.ProtectingDataonCD-ROMs.................... 11 4.1.1.SuitableApproachesforDataProtection.......... 11 4.1.2.ImplementationsprovidingDataProtection........ 11 4.1.3. Efficiency of recent Data Protection Mechanisms . .... 14 4.2.ProtectingAudioContentonCD-DAs............... 14 4.2.1.SuitableApproachesforAudioProtection......... 15 4.2.2.ImplementationsprovidingAudioProtection........ 15 4.2.3. Efficiency of recent Audio Protection Mechanisms . .... 15 4.3.ProtectingDataonDVD-ROMs................... 17 4.3.1.SuitableApproachesforDataProtection.......... 17 4.3.2.ImplementationsprovidingDataProtection........ 17 4.3.3. Efficiency of recent Data Protections ............ 17 4.4.ProtectingVideoContentonDVD-VideoDisks.......... 18 ii Contents 4.4.1.SuitableApproachesforVideoProtection......... 18 4.4.2.ImplementationsprovidingVideoProtection........ 18 4.4.3. Efficiency of recent Video Protection Implementations . 18 5. Legal Aspects 20 5.1.DigitalRightsProtectioninGermany................ 20 5.2.CircumventingCopyProtections................... 20 6. Conclusions 21 A. Appendix 22 A.1.ListingofCDProtections...................... 22 A.2.ListingofCD&DVDProtections.................. 28 1. Introduction This paper was written for the advanced seminar ”CD and DVD Copy protection” accomplished during the author’s ITS master studies at the Ruhr-Universit¨at Bochum. It represents an overview about mechanisms, technologies, and available implementations for protecting optical media discs as a widespread commodity against further and uncontrolled replication. It will further outline options how to circumvent and deactivate copy protections of optical media - but of course without giving details. This report definitely refuses to be considered as some sort of a hacker’s guide to rip contents illegally from Compact Disks (CD) and Digital Versatile Disks (DVD). As a first step in the jungle of protection systems, this paper will commence to classify and assess the operation and performance of several copy protection schemes. But to do so, it is required to start with introducing the reader to the limi- tations and specification of the considered media. This information will barely be necessary for understanding the different variants of hardware based copy pro- tections. The next topic is dedicated to available protections suitable for preventing a CD from being duplicated without authorization. This chapter will also dis- cuss diverse implementation approaches to assess their means and effectiveness. This includes a presentation of ways how to break inefficient CD based protec- tion mechanisms. To accommodate with the different options for CD contents like data and audio, an evaluation will be performed separately of both content types. Accordingly, the DVD as second medium is analyzed using same criteria as al- ready determined for CD evaluation. As a last important fact, the legal aspects of making copies of protected and unprotected media and the employment and development of tools to support this action is highlighted in a separate chapter. The discussion of regulations in pub- lic laws will give a clue if authors and originators of content and software will receive backup support by a country’s legislative. For simplicity, this part will only relate to German laws. Finally, the employment of copy protections for optical media will be discussed as a whole in respect to options what needs to be improved and if it makes sense to ship products with copy protections. 2. Specifying the Medium 2.1. Characteristics of an Optical Data Medium It is evident to have a closer look onto the medium itself. This basic information will help to get a more thorough understanding of protection mechanisms and their technical operation. Both, the Compact Disks (CD) and Digital Versatile Disks (DVD) are disks with normally 12 cm diameter and 1.2 mm thickness. In common, the physical body of such an optical medium is called dye. The disk dye itself comprises a sandwich of a polycarbonate substrate containing pits molded into the upper surface and coated with aluminum. This layer is then protected by a lacquer on which the disk label is printed. The dye for CDs and DVDs measures 15mm diameter centric hole. The audio or computer data is stored between two disk circles of 25 mm (after the lead-in) and 58 mm maximum where the lead-out starts. The basic layout of a CD/DVD/ is depicted in Figure 2.1. Data on an optical disk media is stored using two states Figure 2.1.: CD/DVD Layout which are represented on the surface, the so called pits and lands [Ser02a]. A laser beam is required to focus on the data lane consisting of pits and lands through the clear optical grade polycarbonate plastic. 2.2 CD Specifications 3 The data on the disk is divided into three main areas: • Lead-in (from 23 mm to 25 mm on disk) which contains digital silence in the main channel plus the Table of Contents (TOC) in a subcode Q-channel. It also allows the laser pickup head to follow the pits and to synchronize to the audio or computer data before the start of the program area. The length of the lead-in is determined by the need to store the Table of Contents for up to 99 tracks. A track is a data segment which is placed in one sequence on the disk and represents a logical data group. • Program area (from 25 mm to at most 58 mm) contains up to about 80 minutes or 700 MB of data divided into a maximum of 99 tracks. • Lead-out contains digital silence or zero data. This defines the end of the CD program area. 2.2. CD Specifications On a CD the data is stored in a helix of pits and lands where pits are about 0.12 microns deep and their length varies from 0.8 microns minimum (3 units in length) to 3 microns maximum (11 units in length) depending on the data. The laser which will read out the bits represented by pits and lands operates on a wave length of 780 nm [Ser02a]. The data is arranged in sectors which are the smallest addressable unit for a CD-ROM device operating according to Yellow Book specification. Each sector itself is composed out of 98 frames which build a subunit containing basic data segments like a laser synchronization area, a set of subchannels or control code, 24 bytes of data payload and an error correction code. Frames are intricately interleaved so that damage to the disk will not destroy any single frame, but only small parts of many frames [Sto00]. An important role for copy protection systems is due to the subchannels. They are defined as eight separate one bit channels, each designated by a character from P to W. The subchannels are important for defining the Lead-In, Lead-Out and Track areas of a disk (P-Channel) as well the complete TOC or the remaining time index (Q-Channel). It should be annotated that not all subchannels are in use (R-W are usually empty for most formats). After having shortly discussed the physics of the disk dye, it is evident to highlight the logical disk structure next. Several different formats for arranging data on CDs have been defined. Those ”books” of the Compact Disk family were named for the color of the binder covers in which the specification was issued. Red Book is the specification for CD Audio, Yellow Book is CD-ROM, Orange Book is CD Recordable, Green Book is CD interactive (CD-i), Blue Book is Enhanced CD, and White Book is Video CD. All of these books are based on the Red 4 Specifying the Medium Book physical disk specification, but some also define the types of content the disk may contain, such as 44.1 MHz PCM audio for Red Book, and MPEG 1 video for White Book. Other disk formats, such as Mixed Mode or HFS, do not have books, but are logical variations of one or more of the book formats. For example, the Yellow Book defines CD-ROM as far as the physical characteristics of the disk, addressing schemes, and error correction are concerned, but the file system and type of content can be user defined. A Yellow Book disk could use the HFS file system, the ISO 9660 file system, or a user-defined file system, and could contain text, raw data, or multimedia elements. As copy protections are usually only deployed on Red and Yellow Book CDs, those standards will be subject of investigation in the following. 2.2.1. Red Book The Red Book, which defines CD-Audio, is the compact disk pioneer. The CD was created, after all, to be nothing more or less than a universal delivery medium for one type of content only, namely music digitized at 44,100 samples per second (44.1KHz) in a range of 65,536 possible discrete values (16 bits). The resulting logical format, the Red Book, or Compact Disc-Digital Audio (CD-DA), was defined by Philips N.V. and Sony Corporation in 1980. Data on an audio disk is organized into frames in order to ensure a constant read rate. Each frame consists of 24 bytes of user data, plus synchronization, error correction, and control and display bits. One of the first crucial things to understand about CD-Audio is that its data is not arranged in distinct physical units.