Windows Media Security Issues
Introduction
In the Internet age, security and IPR are sensitive to those who hold copyrighted information. For this paper, the copyrighted information is in the form of songs that are held by music companies. Since the advent of the Internet, a sizable amount of information is available for free; this includes copyrighted information. There are numerous sites offering free downloads of compressed songs that are copyrighted. It is estimated that the music industry suffers a loss of about $5 billion annually.
The music companies and the software industry are exploring ways to counter this free trade and piracy of copyrighted songs. Microsoft, after discussion with the music companies, have brought out a security model that would counter piracy of copyrighted songs. Furthermore, they have also brought out an encoding format that compresses songs to a greater magnitude than most other formats without loss in CD quality.
In this paper, we discuss the features of Windows Media Rights Manager, and how it can prove beneficial to music companies that want to host their songs online in a secure manner.
Windows Media Rights Manager is an end-to-end Digital Rights Management (DRM) System that provides content providers and retailers a flexible platform fpr the secure distribution of digital media files. Content owners can now deliver music, video, and other media over the Internet in a protected format.
- Importance of DRM for Artists and Corporations
- SDMI
- DRM
- Windows Media Media Rights Manager
Importance of DRM for Artists and Corporations
The Internet is the electronic world existing in the public domain where many services are provided at no extra charge - email, software utilities, and music - to name a few. The use of MP3 as a format for exchanging music has caused consternation in the music industry. The music industry, a multibillion dollar global business, feels threatened by the exchange of free music on the Internet. The Internet is a burgeoning electronic behemoth, a labyrinthine maze of interconnected networks where information travels in a flash. The widespread practice of exchange of copyrighted songs has caused consternation in the music industry. It is estimated that the music industry suffers an annual loss of about $ 5 billion because of what it terms as piracy on the Internet.
SDMI (Secure Digital Music Initiative)
To check this rampant piracy, the music industry is looking at various options. The (SDMI) is a forum that brings together the worldwide recording, consumer electronics, and information technology industries to develop open technology specifications for protected digital music distribution. The specifications released by SDMI will enable copyright protection for artists' work by developing a comprehensive system to prevent music piracy. Central to this system is watermarking in which an inaudible message is hidden in music to provide copyrighted information to devices such as MP3 players and recorders. Devices may refuse to make copies of this music depending on the meaning of the watermark contained in therein.
DRM (Digital Rights Management)
Microsoft's Windows Media Rights Manager is an end-to-end DRM system that provides content providers and retailers a flexible platform for the secure distribution of digital media files.
Digital media files can be easily copied and distributed, without any reduction in quality. Thus, digital media is being widely distributed on the Internet through both authorized and unauthorized distribution channels. Piracy is a concern when security measures are not in place to protect content. The Rights Manager addresses these concerns by making it . Content owners can now deliver music, videos, and other media over the Internet in a protected format.
Windows Media Rights Manager
Overview
The music industry estimates a loss of about $ 5 billion annually because of unauthorized access and distribution of music. The Internet contributes to this in no small measure by any means. Hitherto,With Windows Media Rights Manager, retailers and record labels can set up Internet radio stations and music stores to distribute music without any fears. Content providers can breath free by knowing that their media files will stay protected, no matter how widely they are distributed. A very strong DRM encryption scheme is used that would take days of supercomputing time to decode. To further raise the protection level, the content owner can change the media file encryption keys daily or every few hours. In addition, the PC-by-PC licensing policy acts as a strong deterrent to international piracy.
Rights Manager features and benefits
Rights Manager lets content providers deliver songs, videos, and other media over the Internet in a protected, encrypted file format. Windows Media Rights Manager features include the following:
- Secure Distribution of Digital Media
- Flexible Business Models
- Highly Scalable Platform
Secure Distribution of Digital Media
- Persistent Protection - Rights Manager locks media files with an license key to maintain content protection. Each license is uniquely assigned to each computer. This prevent illegal distribution of media files.
- Strong Encryption - Rights Manager includes proven encryption schemes that ensure distributed digital media files are not exposed to piracy or illegal use.
- Individualization - Rights Manager makes each player unique by linking the player to the computer. This prevents a compromised player from being widely distributed over the Internet. with individualization, any compromised player can be identified and disabled from the licensing process.
- Secure Audio Path - Rights Manager ensures content protection in the operating system from the player to the sound card driver in Windows® Millennium Edition. This secure relationship reduces the likelihood that any unauthorized program will capture a digital media stream within a PC.
- Improved Revocation - Windows Media Rights Manager 7 introduces a new level of security, enabling the revocation of compromised players when new players become available.
- Secure End-to-End Streaming and Downloads - Media files are protected during download and on the consumer's PC through secure cryptographic protocols.
Secure Distribution of Digital Media
New licensing rights have been introduced with Windows Media Rights Manager 7 to help enhance the creation of new, innovative business models.
- Separately Distributed Licenses and Media - Licenses are issued independently of the actual media files, providing maximum flexibility and allowing wide distribution of content. Each time a media file is played, Rights Manager checks to see if the consumer's computer has a license. Consumers who do not have a valid license are directed to a license registration page.
- Easy-to-Change Licensing Terms - Because licenses and media files are stored separately, licensing terms can be changed on the server, without needing to redistribute or repackage the media file.
- Innovative Rental or Subscription Models - Content providers can control license start times, stop times, and duration to create innovative business models. Using these different rights enables content providers to optimize their own business rules.
- Limited Play Previews - Using the counted operations (playback) option in the new license structure, content providers can create rental or preview licenses for viewing media files.
- Transparent Licensing - Features such as predelivery of licenses and silent licensing improve the consumer's media experience by removing barriers to acquiring and playing secure media files. Silent licensing means that a content provider may "silently" deliver the license to the consumer, without the need for the consumer to type more information.
- Controlled Transfer to SDMI Portable Devices - Windows Media Device Manager permits the secure transfer of protected media files to Secure Digital Music Initiative (SDMI) portable devices or media.
Highly Scalable Platform
Windows Media Rights Manager 7 is a highly scalable technology ready for implementation in medium to large e-commerce applications.
- Easy Integration - Published application programming interfaces (APIs) are easily integrated with existing e-commerce solutions. Rights Manager can scale to meet the needs of the largest entertainment companies and retailers.
- Streaming and Downloadable Media - This single digital rights management system reduces costs by enabling content providers to secure all digital media assets with one system, regardless of delivery method.
- High-Volume Licensing - High-volume delivery of licenses means that license servers can deliver 500,000 licenses per day on a single server.
- High-Volume Media File Packaging - A single server can protect over 500,000 music files per day.
- COM-based Platform - Component object model (COM) objects are used to protect media files and issue licenses, enabling you to integrate the license acquisition process with your current business model.
- Over 100 Million Installed Players - Support for Windows Media Rights Manager versions 1 and 7 is widespread, ensuring broad compatibility.
How Windows Media Rights Manager Works
- Packaging - The Rights Manager packages the media file by encrypting and locking it with a key. This key is stored in a license which is distributed separately. Other information is added to the file such as the URL from where the license is acquired.
- Distribution - The protected file can be placed on a web server for download, placed on a media server for streaming, distributed on a CD, or e-mailed to consumers.
- License Server - The content provider can stores the specific rights of the license and implements the Windows Media License Service. The consumer's request is authenticated for the license. media files are stored and distributed separately making it easier to manage the system.
- License Acquisition - To play the protected media file, the consumer must acquire the license key to unlock the file. The Rights Manager either sends the consumer to a registration page where information is requested or payment is required, or delivers the license silently.
- Playing the Media file - To play the media file, the consumer needs a player that supports Windows Media Rights Manager. The consumer can then play the media files according to the rights that are included in the license. licenses can have different rights such as start times and dates, duration, and counted operations. if the consumer passes on this protected file to a friend, this friend must acquire his own license to play the media file. this PC-by-PC licensing scheme ensures that protected media files can only be played by the computer that has been granted the license key for that file.
The diagram below illustrates a high-level view of a typical scenario wherein a client requests for a song.
Key
- Client makes a request for a song
- Web server contacts database to see if client fulfills criteria for downloading. Some of the issues
- Registration
- Payment mechanism
- The web server receives the appropriate information to set the stage for downloading
- The web server selects the song that the client has requested from the song database
- The packaged song is ready for download along with the license
- The client receives the packaged song
THE BIG PICTURE
In the above diagram, the encoding, packaging, and distributing functionalities have may logical or physical separation:
- The content owner encodes the WAV files to WMA format.
- The content packager packages the WMA file i.e. encrypts and protects the file using Windows Media Rights Manager
- The content distributor delivers packaged WMA files to consumers
- The license issuer - or Windows Media License Server - resides in the Web Server and issues licenses for WMA files, either before of after a WMA file is played, or in response to a license request by a consumer's player
- The consumer plays the packaged WMA file. If the license is not found for the WMA file, the player requests the license. If the consumer does not have a WMRM client on his player, he is redirected to a URL from where he can download a player that has the WMRM client.
Encoding
- Codecs
- Profiles
- Batch Encoding
- Remote Administration
Codecs
Codecs are software used to compress audio or video data. Windows media audio and video are codecs used to decrease the bit rate of digital media files so they can be delivered efficiently over the network. Windows Media Encoder uses these codecs for compression, while windows media player decompresses the data for playback.
Profiles
A profile is a group of settings that match content type and bitrate with appropriate audio and video codecs. The windows media encoder can convert WAV and MP3 files to WMA format using a variety of profiles. The profiles of interest are:
- Audio for CD Quality (96 kbps)
- Audio for CD Quality transparency (128 kbps)
- Audio for near-CD Quality (64 kbps)
A sample WAV file of size 117 MB was encoded using the above profiles. It yielded the following results:
64
5.36
21.828
95
8.02
14.588
128
10.6
11.038
Batch Encoding
The Windows Media Encoder can encode multiple audio files. These files can be stored in a specific folder which is then traversed; or the files may be stored in various locations; these file paths are recorded in a text file.
Remote Administration
An administrator can control an instance of Windows Media Encoder running on a remote computer. The administrator can:
- Connect to and control a specific encoder
- Monitor the status of the encoding process
- Create encoder engines
Packaging
Packaged WMA files are files that have been protected using WMRM. Only files with ASF, WMA, or WMV extensions can be encoded.
- Cruptographic primer
- Key generation
- Content header generation
- File protection
The following diagram outlines the packaging process
Cryptography Primer
Cryptography is the science of using mathematics to encrypt and decrypt data. Cryptography enables one to store information or transmit it across insecure networks (such as the Internet) so that it cannot be read by anyone except the intended recipient.
Data that can be understood without any measures is called plaintext. The method of disguising plaintext by ina manner that would hide its substance is called encryption. Encryption results in human unreadable a file called ciphertext. The process of reverting ciphertext back to its plaintext is called decryption.
How cryptography works
A cryptographic algorithm or cipher is a mathematical function used in encryption and decryption process. A cryptographic algorithm works in combination with a key - a word number or phrase - to encrypt the plaintext. The same plaintext encrypts to different ciphertext with different keys. The security of the encrypted data depends on two factors - the strength of the encryption algorithm, and the secrecy of the key.
Conventional cryptography
In conventional cryptography, also called secret-key or symmetric-key encryption, one key is used for both encryption and decryption. The figure below is an example of the conventional encryption process. Conventional encryption is very fast especially useful for data that is not transmitted. However,conventional encryption as a means for transmitting secure data can be quite expensive simply due to the difficulty of secure key distribution.
For a sender and recipient to communicate securely using conventional encryption, they must agree upon a key and keep it secret between themselves. The danger of interception increases if the sender and recipient are in different geographical locations; they must trust a secure communications medium to prevent disclosure during transmission.
The persistent problem with conventional encryption is key distribution
Public Key Cryptography
The problems of key distribution are solved with public key cryptography. Public key cryptography uses a pair of keys for encryption - a public key for encrypting data, and a private key for decrypting data. The user publishes his public key to the world while keeping his private key secret. anyone who has a public key can encrypt information but cannot decrypt it. Only the person who has the corresponding private key can decrypt the encryption.
The primary benefit of public key cryptography is that people who do not have any preexisting security arrangement can exchange messages securely. The need for sender and recipient to share keys through some secure chanel is eliminated; all communications involve public keys; no private keys is ever transmitted or shared.
Keys
A key is a value that works with a cryptographic algorithm to produce a specific ciphertext. Keys are very large numbers measured in bits. In public key cryptography, the bigger the key the more secure the ciphertext. Public key size and symmetric key size are totally unrelated. A conventional 80-bit key is equivalent ot a 1024-bit public key.
While the public key and private key are mathematically related, it is very difficult to derive the public key given only the private key - it requires tremendous supercomputing power and not all users have access to supercomputers.
Digital Signatures
A major benefit of public key cryptography is that it provides a method for employing digital signatures. Digital signatures let the recipient of the information verify the authenticity of the information's origin, and also verify that the information was not tampered during transit. Thus public key digital signatures provide authentication and data integrity. A digital signature also provides non-repudiation - it prevents the sender from claiming that he or she did not send the information.
Instead of encrypting information using someone's public key, it is encrypted with the sender's private key. If the information can be encrypted with the sender's public key then it may be safely assumed that the information originated from the sender.
Key Generation
The WMRMKeys object generates the keyID, license key seed, key, private key, and public key.
- KeyID - The keyID is a value that identifies the key for a WMA file. this value is used to identify which license to issue from server and which license to use for client.
- License key seed - The license key seed is a shared secret value that is used to generate keys to encrypt Windows Media files. The license key seed must be shared between the person or organization that packages the Windows Media files and the license issuer.
- Key - is created from the keyID and the license key seed; it encrypts the WMA file.
- Private key - a value that is used to sign content headers during the packaging process. It is also a value used by license issuers to sign licenses when they are issued.
- Public key - a value that is used by the license issuer to verify that the signature in the content header has not been tampered with. It is also used by the DRM component in the player to verify that the content header has not been tampered with.
From the keyID and the license key seed, the WMRMKeys object generates a key. This key is used to encrypt the WMA file.
Header Generation
The WMRMHeader object, together with the key, keyID, contentID, and license acquisition URL, is used to create the content header.
To increase security and prevent tampering, the content header must be signed with the private key. For the license issuer to verify the signature, the public key must be shared with the license service.
- Content header - is a string that contains the following information - keyID, and license acquisition URL. optionally it can contain the contentID, attributes, and required individualization number.
- License acquisition URL - This points to the first web page that appears in the license acquisition process. This URL is included in every packaged WMA file. When a consumer tries to play a WMA packaged file that is not licensed, the player opens the license acquisition URL to acquire the license. Only players with DRM clients can acquire licenses.
- Attributes - can be added to the content header. They may be added to identify the source of the WMA file, the content owner, version number of the WMA file etc. these features allow the content owner, the content packager, the content distributor, and the license issuer to securely communicate track information about the file. the following attributes can be added to each content header:
- copyright, content type, artist name,
- artist web site URL, title,
- license distributor or issuer,
- license distributor URL,
- content distributor
- rating, and description
- ContentID - is a value that uniquely identifies the WMA file. this should be unique for the piece of content and is optional.
- Individualized Players - an individualized player is one whose DRM component has been individualized; it is like receiving a security upgrade. An individualized application is one in which the DRM secret value is different from all other applications. With individualized DRM components, a security attack on a DRM system should only.
If a consumer tries to playa WMA file that requires individualization on a player that has not been individualization, a license is not issued and the player prompts the consumer to get a security upgrade.
The content header is signed with the public key; for the license issuer to verify the signature, the public key must be shared with the licensing service. Before issuing the license, the license issuer can verify the validity of the license by using the content packager's public key. If these signatures do not match, the license is not issued.
File Protection
Ater generating the keys and the content header, the WMA file is now ready for protection. The WMRMProtect object encrypts the file, and packages both the encrypted content and the content header in a WMA file.
Rights
Rights specify how a consumer can play a WMA file and define any other actions that are allowed such as allow for play on PC, the number of times a song can be played, license duration, song transfer, etc.
The following rights are provided by the Windows Media Rights Manager:
- Using WMA files on a Computer
- Licenses
- Transferring WMA files
- Security Levels
Using WMA files on a Computer
- AllowPlayOnPC - allows the consumer to play the WMA file on the computer. This right is set by default.
- PlayCount - specifies the number of times the consumer is allowed to play the WMA file. By default this right is not set; unlimited plays are allowed.
- AllowBurnToCD - specifies if the consumer can copy the WMA file to a CD. By default this right is set.
- BurnToCDCount - specifies the number of times the consumer can burn the WMA file to a CD. By default this right is not set; unlimited copying is allowed.
- AllowBackupRestore - allows the consumer to manage licenses by backing up and restoring them. Consumres can restore licenses on the same computer or to different computers. By default this right is set.
Rights for Licenses
- BeginDate - specifies the date from which the license is valid. Before this date the WMA file cannot be played. By default this license is valid immediately.
- Expiration Date - specifies the date after which the license is no longer valid; the Windows Media file can no longer be played. By default this right is not set and the license never expires.
- DeleteOnClockRollback - this right deletes license if the consumer's computer clock is rolled back to an earlier time. By default this right is not set.
- DisableClockOnRollback - disables a license if the computer's clock is rolled back. The license is enabled again when the clock is corrected. By default, this right is not set.
Transferring Windows Media files
When a WMA file is transferred, a portable license is also created. The following rights are applicable for portable licenses.
- AllowTransferToNonSDMI - allows the consumer to transfer the WMA file to non-SDMI-compliant portable device. By default, this right is set.
- AllowTransferToSDMI - allows the consumer to transfer the WMA file to an SDMI-compliant device. By default, this right is set.
- TransferCount - specifies the number of times a consumer can transfer a WMA file to SDMI-compliant portable devices. By default, this right is not set; unlimited transfers are allowed.
- PMRights - specifies the rights given in portable licenses. By default this right is set to 19, which specifies the rights in the portable license to play the file on a portable device and transfer it.
- PMExpirationDate - specifies a date when a portable license expires. On expiry, the file cannot be transferred from the computer or portable device. if the portable license expires on a portable device, the file can no longer be played. By default this right is not set.
Security Levels
The application security level is a value that ranks the security of a playback device. Different device applications have different levels of security. For example, a playback device with a high security level can play SDMI-compliant content, whereas a less secure application cannot.
A minimum application security can be specified for playing WMA files. On playing a file, the minimum application security level specified in the license is compared to the application security level of the playback device. the result determines whether the file can be played.
What does the security level indicate to the content owner? The content owner can decide if he wants the WMA files to be available to a wide market (requiring low security level) or to restrict playback to very secure playback devices (requiring high security level)
The following table shows application security levels for different playback levels.
150
Application that produces clear content
Windows Media Player for Pocket PCs
450
The first level of security intended to meet the level of the SDMI specifications; portable media must have a hardware serial number
SDMI-compliant playback devices
1000
Audio players
Portable players
PCs with software obfuscation (software code with hidden information)
Windows Media Player
2000
PCs with protected audio stacks
Windows ME
The following rights specify the minimum security levels for playback devices:
- MinimumAppSecurity - the minimum security level that is required of a player application. By default this right is set to 150.
- PMAppSecurity - minimum security level required of a portable player or portable media. The default value is 150.
License Generation
- Issuing Licenses
- Reissuing Licenses
To play a packaged file, the consumer must obtain a separate license containing the key. The license for a WMA file is linked to the computer to which it is issued. Consumers can share the WMA file but each recipient must have a license to play it. In addition to unlocking files licenses can contain rights and other properties that specify the use of the WMA file. The properties are configured in the license separate from the WMA file, allowing for the issue of different licenses for the same WMA file and change license properties on the fly. For example, to promote a song the content owner can distribute a WMA file to an electronic mailing list with a license that enables consumers to play the song five times. When consumers purchase the song, a new license with the right to unlimited playback is issued. The following diagram shows the basic process for delivering packaged WMA files and issuing licenses.
To generate a license, the license issuer uses the license key seed with the keyID in the WMA file to generate the key, and then specifies the rights. The license issuer uses the Windows Media License Service to issue the license and bind it to the consumer's computer. Each license contains the following information:
- The key to unlock the WMA file
- The rights and conditions of the license
- Priority of the license with respect to other licenses for the same WMA file
- Attributes - name and description of the license
Issuing Licenses
- Pre-delivery
- License request delivery
- Non-silent
- Silent
- Version 1 and version 7 license delivery
The process of issuing a license is illustrated in the following diagram
- The player sends a request for a license to the windows media license manager
- This request - called a challenge - is received and put into a WMRMChallenge object. The challenge contains the content header, information about the consumer's computer, and a list of requested rights.
- The WMRMRights object generates the rights to be put into the license.
- The content header information is put into the WMRMHeader object to retrieve a keyID
- The keyID and license key seed are put into the WMRMKeys object to generate the key.
- The client information, the rights, the keyID, and the key are put into the WMRMLicGen object to generate the license. the license is put into the WMRMResponse object to generate a response that is sent back to the consumer and put into the license store on the consumer's computer.
Pre-delivery - the license is delivered before the WMA file is downloaded. A consumer, selects a song and purchases it; a license is issued. Then the consumer downloads the song and can play it immediately. the consumer is not required to follow additional steps to acquire a license after acquiring the WMA file.
License request delivery - the license is delivered in response to a license request which is made by the consumer's player. The consumer is allowed to download the packaged song. When he tries to play the song:
- Non-silent delivery - on requesting the license, the WM Licensing Service prompts the consumer for more information. A web site might request the consumer to provide an e-mail address for make payment for a license.
- Silent delivery - the licensing service has the required information; the consumer does not have to furnish any information. He may have registered or paid a subscription fee.
Version 1 and version 7 license delivery - this method accommodates those who have players that support only WMRM version 1. for a license request, both version 1 and version 7 licenses are issued to the consumer, who can now play the WMA file on a version-1 and version-7 enabled players If the consumer is using a version 1 player, only a version 1 license is issued.
Reissuing Licenses
Previously issued licenses can be reissued to the customer. A consumer's computer may be damaged or replaced; he might want to recover all the licenses issued to him. If backup and restore of licenses is not allowed, the only way for the consumer to recover licenses is for the site to reissue them. The content owner can set his own policy for reissuing licenses. For each license transaction, the userID and keyID for which the license was issued must be recorded, and the rights if the same type of license is to be reissued.
Conclusion
Windows Media Rights Manager provides music companies with safe and secure options to host their copyrighted songs on the Internet. It provides a great deal of flexibility in combining the rights model with a revenue model dictated by the content owner.
The use of encryption and public key cryptography provide a very secure environment for the content owner. Based on the various rights - playing, transfer of songs, portable player rights, and security levels, the content owner can devise a flexible revenue model based on these rights. Furthermore, the licensing options - pre-delivery i.e. before a song is downloaded, and post-delivery, after the song is downloaded - widen the scope of the revenue model.