A reliable optical disk identification technique for protection purposes☆
Graphical abstract
Introduction
Optical disks are used for the distribution and backup of any type of digital content, such as software applications, multimedia applications, games, books, and maps. There are many types of optical disks available in the market, such as CDs, DVDs, and Blue-Rays. While CDs and DVDs are commonly used for the distribution of digital content, Blue-Rays are used for backup purposes. Almost all computer systems have a CD or CD/DVD drive.
Every year, the education and entertainment sectors produce thousands of new titles or new versions of the existing titles. Sometimes, individual authors produce their titles and distribute them directly or indirectly. Therefore, millions of copies are produced, distributed, and then sold to end users. This number has been slightly affected by the increasing use of the Internet to distribute software. Moreover, optical disks are still being used for distributing copyrighted digital content.
This considerably large industry of software distribution through CDs and DVDs is threatened by piracy [1], [2], [3]; the entire content of an optical disk can be duplicated using any optical disk drive with write support. Nowadays, most PCs and laptops come with a very fast CD/DVD writer. Further, there are many copy machines that can write to a batch of writable disks at once.
Piracy affects the optical disks industry and causes losses that amount to millions of dollars. In order to counter piracy, digital content providers use different copy protection techniques to protect their copyrights. There are many such techniques that provide different security strengths [4].
Strong techniques [5], [6], [7], [8] are very complex to apply and require a special manufacturing process. These techniques are secure but suffer from many problems. Normally, they support a subset of optical disk drives, particularly the new ones. Sometimes, they fail to identify a disk and prevent legal users from using their software. Some other times, they take a considerably long time to perform the optical disk identification. Hence, these strong copy protection techniques are not used.
Average and weak techniques [7], [9] are commonly used for optical disk protection because of their stable performance at end-user computers. Companies decide to choose weak techniques to avoid the dissatisfaction of customers. Their point of view is as follows: It is sufficient to reduce piracy to a certain percentage and satisfy customers instead of preventing the piracy completely and dissatisfying their customers.
The main challenge for strong copy protection techniques is to support all types of optical disk drives with any capability and in any condition. However, any special protection technique could lead to an unstable response in the case of some drive types. The failure of a single drive type affects thousands of users.
Optical disk drives may have different capabilities and may function under different conditions; this may lead to an unstable performance or a false result. Optical disk drives with different capabilities such as the support of CDs or DVDs or both, ability to read or read/write variables or at a constant reading speed, weak or strong lenses, hardware detection and correction of errors, automatic error recovery, and variable read/write speed.
Optical disk drives function under very different conditions. Further, new drives exhibit different performance levels compared with old drives. The long usage adversely affects the performance of the mechanical system, and the presence of dust adversely affects the lenses and the reading process. Further, optical disks may suffer from scratches and may be covered with a thin layer of dust. Scratches and dust adversely affect the reading operation and impose a delay in the case of some drives. Some drives have the special capability to overcome reading errors inside the hardware without affecting the reading performance. Other drives have an intermediate solution with a very different performance.
The protected software should identify and then check the originality of an optical disk. The software should use the optical disk drive to apply the identification technique. Optical disk drives may provide various services depending on the brand and the type of these drives. Hence, it is necessary to use only the common services supported by any optical disk drive even the very old drives.
It is known that the optical disk drive is a measuring unit. It used for measuring a signal related to the inserted disk. The signal may vary from one technique to another. It could be digital content or a dynamic behaviour that varies depending on the supplied parameters. Further, the captured signal may suffer from variation and noise depending on the device and disk configurations and conditions.
In order to develop an optical disk identification technique, we need to solve the problems of a noisy signal and the variation of system parameters. Hence, we need to build a simulation model for optical drives and to study the behaviour of the measured signal and the noise.
The rest of this paper is organized as follows: Section 2 states the optical disk characteristics. Section 3 presents the optical disk drives characteristics. Section 4 provides an overview of the existing digital content protection techniques. Section 5 provides an overview of the existing optical disk identification techniques. Section 6 introduces the proposed technique. Section 7 presents the proposed model for the optical disk. Section 8 describes the proposed model for the optical disk drive. Section 9 introduces the proposed model for the entire system. Section 10 discusses the development of the simulation software. Section 11 presents the verification of the entire system model. Section 12 describes the proposed identification technique for optical disks. Section 13 presents the new optical disk protection technique. Section 14 discusses the actual implementation of the technique in the industry. Section 15 presents the conclusion and briefly describes the future work.
Section snippets
Optical disk characteristics
Two major types of disks are commonly used [10]. The compact disks (CD) and the DVDs. CDs can hold information up to 650 MB, and single-layer DVDs can hold up to 4.7 GB. CDs are normally used for storing software applications, videos in VCD format, and 65-min audio tracks. DVDs are used for storing software applications with a large amount of content and high-quality video and audio files.
Digital content consists of bits. Bits are represented using eight to fourteen modulation (EFM) [11], [10],
Optical disks drives characteristics
Optical disk drives are responsible for reading the digital content of optical disks. They use a laser beam for detecting the changes between hills and lands. Different laser frequencies are used for penetrating the layers and reading multi-layer DVDs. The optical system used for reading the content is called the head.
The head motion is controlled by a motor. This motor produces a linear motion to move the head from one track to another. Another motor is used for rotating the disk. The disk is
Introduction to digital content protection techniques
The purpose of digital content protection is to prevent the illegal distribution of copied content. Thus far, many techniques have been developed to do so [2]. This section provides an overview of the existing techniques irrespective of whether they depend on the optical disks or not.
Optical disk content protection techniques
This section discusses the optical disk protection techniques mentioned earlier in detail. The basic idea is to alter the manufacturing process of the optical disk. The alternation may prevent the normal copying of a disk or can be identified by the protected software. Some of the following techniques are published as patents, and the others are known in the optical disk piracy societies.
Proposed technique
Clearly, none of the optical disk protection techniques can provide an efficient way to stop piracy. Some techniques provide weak protection with stable performance; the other techniques provide strong protection with unstable performance. This instability can be attributed to the following reasons:
First: It is required to support very old optical disk drives. Some drives are not able to perform any operations except reading. Operations such as reading device configuration, acquiring writing
Optical disk mathematical model
Bits are arranged in a spiral (Fig. 6) shape along disk tracks [10], [20]. Normally, original disks contain one track, and several tracks are used by writable disks to allow users to append content.
A track starts from the inner radius (≈25 mm) and extends to the end of the stored data. The outer radius may vary depending on the content; for instance, in the case of a 650-MB CD with normal specifications, the outer radius is ≈58 mm. Two factors affect the value of the outer radius, the TRP and the
Optical disk drive dynamic model
The optical disk drive consists of three mechanisms, namely the rotational mechanism, the seeking mechanism, and the disk insertion/removal mechanism. The third mechanism is out of scope because it does not affect the reading operation.
The rotational mechanism consists of a brushless DC motor and a speed-control circuit. Some models use the sensor-less type for a longer life time and low power consumption.
The seeking mechanism consists of a servo DC motor and a position-control circuit. Stepper
System model
In order to develop an identification technique for the optical disks, we need to understand the system behaviour under different parameters and conditions. It is not easy to have all drive models or to manufacture optical disks with different parameters. Hence, we need to build a simulation model for the system. The system model consists of the following components: the angular speed control module, the head position control module, the gearing system, the optical disk model, and the digital
Simulation software development
The proposed system model is implemented using C/C++ in order to carry out the simulation simultaneously with the actual experiments. The system consists of optical disk and disk drive models. The entire system is illustrated in Fig. 12. The optical disk model is directly used by the final identification technique to predict the system behaviour and compare it with the actual results. Further, in order to simulate the control elements, a simulation library is developed. The library uses
System model verification
In order to test the system model, we need to conduct two types of tests: internal tests and external tests.
The purpose of internal tests is to examine the internal behaviour of the system after applying a set of read commands. Signals like head position and angular speed can be recorded and analyzed in these tests. Further, such tests can be applied to the proposed system model. It is difficult to measure the internal signals in the real system case.
The purpose of external tests is to examine
Original disk identification technique
The purpose of the identification technique for optical disks is to determine the deviation of the manufacturing parameters in order to differentiate between original disks and copies. There are three parameters to consider: BPL, which is the starting radius of the data; SVY, which is the scanning velocity that directly affects the bit width; and the TRP, which is the track pitch.
According to the existing CD standards, the SVY value may vary between 1.259 m/s and 1.261 m/s. TRP may vary between
Optical disk protection technique
As described in the section on the proposed identification technique, there is a noticeable variation between the behaviour of the copied disks and that of the original disk. From the experiments, it is clear that there is a variation in the slope. However, there are many time shifts and considerable noise. Therefore, we need to develop an algorithm to calculate the variation in the slope and to ignore the time shift and the noise. This section proposes such an algorithm.
Fig. 29 shows the
Final implementation
It is important to ensure that this technique works successfully in any optical disk drive and under any operating condition. Thousands of drive models are available in the market or at end-user computers. The operating condition may also depend on the condition of the drive, the disk, the computer, and the operating system.
Hence, it is important to perform a wider test. A real sample with demo software is produced. The demo software is programmed to report the testing conditions and results to
Conclusions
The proposed technique succeeds to differentiate between original optical disks and copies. It requires manufacturing the disk with special TRP value without affecting the reading stability. Any factory can apply this configuration without a need for special equipments. Also, the proposed technique does not require reserving a data area for protection purposes as required by other techniques.
Furthermore, the proposed technique uses the disk drive as a measurement device and the time of read
Mohamed Sobh received the Ph.D., M.Sc., and B.Sc. degrees in Computer Engineering from Ain Shams University in 2006, 2002, and 1996, respectively. He is an Assistant Professor in the Department of Computer and Systems Engineering, Ain Shams University, Cairo, Egypt. His research interests include cryptography, software protection, cloud security, computer programming and algorithms, and computer simulation and modelling.
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Cited by (0)
Mohamed Sobh received the Ph.D., M.Sc., and B.Sc. degrees in Computer Engineering from Ain Shams University in 2006, 2002, and 1996, respectively. He is an Assistant Professor in the Department of Computer and Systems Engineering, Ain Shams University, Cairo, Egypt. His research interests include cryptography, software protection, cloud security, computer programming and algorithms, and computer simulation and modelling.
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Reviews processed and recommended for publication to Editor-in-Chief by Associate Editor Dr. Khurram Khan.