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...watermarking to discourage and detect piracy through a registration-based system. In the second approach, based on the parallels between games and premium audio and video content, we propose the use of current physical-media copy-protection technologies for gaming content. In particular, we focus on broadcast encryption technology. The use of an open, standard-based architecture enables the development of a more restrictive protection system for games. Finally, we demonstrate how the proposed protection mechanisms can be applied to video-game copy protection through five scenarios.
INTRODUCTION
Before the extensive availability of the high-speed Internet, the distribution of pirated software involved the transfer of a physical copy, that is, the transfer of a storage device such as a diskette or a compact disk. This limited the rate at which illegally copied games could be distributed, and thus the associated losses could be absorbed. However, the recent advances in technology, the ease of access to the Internet, and the widespread use of peer-to-peer applications made the physical copy obsolete. Software piracy is now a widespread, decentralized problem in which millions of people take part. The protection afforded by the legal system is no longer easy to enforce or cost effective. Thus, the gaming industry now relies on technological mechanisms to deter, detect, and prevent piracy.
In 2004, when sales of video games in the United States set a record at $7.3 billion, (1) the industry lost more than $1.8 billion to global piracy. (2) Unfortunately, the lost revenue is due to a variety of different piracy-related attacks, such as illegal copying, counterfeiting, and distributing. The ramifications associated with piracy propagate throughout the gaming community. The obvious victims are the game-producing companies, but the more peripheral victims are often not recognized. Hardware producers rely on video game players to buy the newest, fastest, and most expensive products to play increasingly resource-intensive new games. For example, in September of 2003 a significant portion of the source code of the game Half-Life ** 2 was stolen. When the theft, which occurred before the release of the game, was discovered, the game maker delayed its release in order to develop a new and different version of the game. This delay led to potential revenue losses for ATI, a graphics card company. As a marketing strategy to entice consumers to upgrade, they planned to distribute free versions of the game with their latest graphics. Due to the delayed release, the game was not available in time. The video game industry must also contend with unscrupulous retailers who are able to significantly increase their profits by producing and selling illegal copies.
To develop techniques for the protection of gaming content it is necessary to understand the mechanisms used by attackers to bypass copy-protection technologies. The attack mechanisms in use today target both the executable software and the console devices on which many games are played. In this paper we are concerned with the following types of attacks:
1. Sharing of installation media (e.g., illegal sharing of an installation CD from a legally purchased game package).
2. Creating and distributing illegal copies of installation media.
3. Disabling or bypassing copy-protection technology so that the game can be illegally redistributed (e.g., disabling the license check by modifying the game code).
4. Execution of illegally copied games on a traditional PC.
5. Execution of illegally copied games on a console gaming system.
6. Execution of illegally copied games on a gaming system that has been modified to run games using alternate media formats such as a standard CD.
It is important to note that the third type of attack, in which the game itself is modified, is distinct from the last one, in which the gaming system is modified. Modification of the gaming system to bypass copy protection is commonly referred to as modding.
In this paper we present two novel approaches for game protection. The first approach is based on a particular software watermarking technique, the branch-based software-watermarking algorithm, developed by the authors at the IBM Almaden Research Center. (3) Software watermaking is one of many techniques currently being studied to prevent or discourage software piracy and copyright infringement. The basic idea of watermarking is to embed a unique identifier in the program. Depending on the identifier, it can be used to indicate the author or the legal purchaser of the program. By incorporating ideas from code obfuscation (to aid in preventing reverse engineering) and software tamper detection (to thwart attacks such as the application of semantics-preserving transformations), the technique makes it possible to detect theft through the implementation of a registration-based system. The algorithm involves redirecting branch instructions to a special function known as a branch function. This function is responsible for computing the program's "fingerprint" and controlling the execution. The branch-based software-watermarking algorithm makes several improvements over previously proposed watermarking techniques:
* The technique simultaneously provides proof of authorship and the ability to trace the source of the illegal distribution.
* The technique demonstrates a significantly higher level of resilience to attack without significant overhead.
* The technique provides a means for distributing prepackaged, fingerprinted software whose link to the consumer is established at registration time.
In the second approach we show how games are similar to premium audio and video content in their need for copy protection. Based on these parallels, we propose the use of current copy-protection technologies for physical media in the battle against video game piracy. In particular, we focus on the broadcast encryption technology developed by 4C Entity, LLC, a consortium founded in 1998 by IBM, Matsushita Electric Industrial Corporation, Toshiba Corporation, and Intel Corporation to implement CPRM (Content Protection for Recordable Media). In this scheme, the game executable is stored in an encrypted state on a disk and depends on the presence of protected media (such as an SD memory card) to execute. As a consequence, multiple copies of a game can be created by an end user, but they cannot be executed concurrently. This is a more user-friendly approach than a per-PC license, which does not allow an end user to install a game on a second machine.
Content protection in the gaming industry is obviously an area of intense interest for developers and producers of games. It is also of interest to game device makers, who often sell the device at a loss and instead draw their profit from royalties on software sales. Unfortunately, the gaming industry currently makes use of proprietary methods in the development of copy-protection technologies. Whereas this approach is generally effective against the occasional copier, such protection is usually vulnerable to an attack by an experienced hacker. Our approaches are based on open standards: the branch-based watermarking algorithm is publicly available, and the techniques for protection of physical-media content are based on open standards. Consequently, the techniques we discuss here are likely to be scrutinized for pitfalls by a large community, are based on a strong technical basis, and are likely to lead to more robust protection mechanisms for games.
The rest of the paper is structured as follows. In the section "Gaming and piracy," we present an overview of the state of the art in copy-protection technologies for PC and console-based gaming. Then, in the section "Using software watermarking to combat game piracy," we discuss our branch-based software-watermarking algorithm and the ways it can be used to prevent game piracy. In "Content protection for physical media," we briefly review the evolution of copy protection for audio/ video content and for recordable media, with a particular focus on broadcast encryption, a cryptographic-key management technology. Finally, through five deployment scenarios described in the section "Content protection for games: Deployment scenarios," we demonstrate the viability of the proposed techniques to prevent common game piracy attacks. We thus demonstrate that current copy-protection techniques that were developed either for software or for video and audio content can be successfully applied to combat piracy in video games. In the "Conclusion" section, we summarize our main results.
Throughout the paper we use a variety of terms which could have multiple meanings. This paragraph clarifies our usage. We use the term video games (or games, for short) to refer to games that are played either on a PC (PC-based game) or specialized hardware known as a video game console (console-based game). The techniques we discuss here apply both to prepackaged games and games that are downloaded from the Internet.
Whereas copy protection refers to preventing copying of copyrighted material, content protection is more general and includes other violations of intellectual property, such as performing illegal modifications to proprietary software. We use the term premium audio and video content interchangeably with premium entertainment content. We use the term optical media to refer to media such as the compact disk, for which the reading or writing of information is performed through optical techniques. We use the term hackers to refer to people involved in software piracy.
GAMING AND PIRACY
To combat the high level of piracy, the video game industry has taken a variety of actions that include both deterrent and preventative techniques. In this section we present the current state of the art in both hardware- and software-based protection mechanisms.
Hardware-based protection techniques
A variety of hardware-based techniques have been used in video game anti-piracy measures. These techniques are typically able to provide a higher level of protection than their software-based counterparts. However, the techniques are generally more expensive to produce and often cumbersome for the end user.
One of the first hardware-based, anti-piracy techniques deployed in the game industry was the dongle. (4) The dongle, a hardware device commonly distributed with a piece of software to prevent unauthorized execution, is typically connected to an I/O port, such as a serial or parallel port. As the software executes, it periodically queries the dongle, which returns the output of a secret function. If communication fails or the result of the query is incorrect, the software will eventually produce incorrect results or fail entirely.
The use of a dongle as a protection mechanism has several drawbacks, the first of which is the cost. The cost of the dongle, approximately $10 in the United States, further increases the cost of the game. Second, the use of a dongle limits the distribution options. In particular, when a game is sold and distributed over the Internet, the inclusion of a dongle is not feasible. Finally, code for dongles is often "cracked" shortly after release. This is generally accomplished by "disassembling" the game code, identifying the calls to the dongle, and then bypassing those calls. After the dongle is cracked, a code patch is usually distributed so that anyone can play the game without the required dongle. Such an instance occurred with the Robocop ** 3 game for the Amiga ** platform. The antipiracy dongle had to be connected to one of the joystick ports for the game to run. A few days after its release in April of 1992, the dongle was cracked.
A second hardware-based piracy prevention technique is tamperproof hardware. (5) Tamperproof hardware is a way to secure parts of the hardware, such as the use of a computer chip, from being observed by a hacker. By executing the software in a secure context the pirate is unable to gain access to the application code and identify the code to be bypassed. This piracy prevention technique is feasible for console-based systems but has limitations for PC games. Because a user must purchase a console to even play a game, the game developers can make use of this technology, but the additional cost of requiring all PC game users to have tamperproof hardware is not currently a viable solution.
The development of the Trusted Platform Module (6) (TPM) is one example of using tamperproof hardware to prevent software tampering. The TPM is a special chip developed to enable trusted computing features. The four essential features include:
1. Secure I/O--Input and output are verified by performing a checksum of the software used for I/O.
2. Memory curtaining--The hardware prevents a program, including the operating system, from reading or writing memory used by another program.
3. Sealed storage--Information is protected by encrypting it with a key derived from the hardware or software currently being used.
4. Remote attestation--Changes to the computer are detected by having the hardware generate a certificate stating what software is in use. The certificate is presented to the remote party, generally through the use of public key cryptography, to demonstrate that the system has not been altered.
The TPM features have been incorporated into chipsets by Intel Corporation, Advanced Micro Devices, Inc., and IBM.
One mechanism used by hackers to bypass copy protection is the mod chip. This is a special chip added to the game console that is capable of modifying or disabling security mechanisms. Through the use of the mod chip a user can play games from other regions (installation CDs implement restrictions that make the game functional only in certain geographic areas) and create backup copies on CD-R and DVD-R media. Although it is legal in some countries for the purchaser to make a back-up copy in case the original is lost or damaged, game consoles contain protection mechanisms that prevent the user from playing the copies. The mod chip makes it possible to bypass these protection mechanisms by supplying the appropriate information. Currently, this is a very common attack mechanism for popular console systems such as the Xbox ** and PlayStation ** 2. In fact, Microsoft has taken action to prevent those who have modified their consoles from Xbox Live ** play (7) (online environment). When a user logs onto an online gaming forum, his or her system is checked for the presence of mod chips. If mod chips are detected, the unit's serial number is recorded, and the device is permanently banned from the network. As a counterattack, mod chips are being produced that can be temporarily disabled to prevent detection.
Software-based protection techniques
The success of online gaming has led to a new set of concerns for the industry. These concerns revolve around maintaining a fair and consistent gaming environment in which players will continue to participate. If some players are able to modify their games, for example, by making their character immortal, the entire gaming experience can suffer. One technique that has been explored by researchers and that could...
NOTE: All illustrations and photos
have been removed from this article.
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