Controlled derivative rights on the digital content
FIELD OF THE INVENTION
The present invention relates to methods, devices, data signals and memory storage for digital rights management of distribution and control of items such as digital content. In particular the present invention relates to derivative rights on the digital content.
BACKGROUND OF THE INVENTION
In a Digital Rights Management (DRM) system, different types of rights have been defined [B. Rosenblatt, Digital Rights Management: Business and Technology, Hungry Minds Inc., U.S.]. Typical rights expression language (REL) such as XrML and ODRL are sufficiently flexible to capture these rights which include rendering of digital content such as play, view or read; transferring of digital content such as give, loan or sell; and derivative rights of digital content which include extract, embed and edit.
Rendering and transferring of digital content have previously been described extensively in DRM and authorized domain [US2005/0060571, US20050210261 US2003/0023564, US6824051B2]. A typical embodiment is an authorized domain of a DRM-system, where there are a number of compliant devices. Each of these devices has a built-in DRM Client (a firmware or a software tool) which is capable of interpreting a license (constructed by a REL) and enforcing the rights and states correctly corresponding to the license. Therefore, each device in the domain needs an approved license in order to render or transfer the digital content.
Management of derivative rights and how derivative rights can be enforced correctly and securely in a DRM system and the effects of derivative rights on the license and the associated content have not been described explicitly in the early work. The derivative rights are useful from the user's perspective, because the user's experience in using the digital content can be expanded while his/her convenience in using the digital content can be improved. For instance, the following scenarios require derivative rights:
1. A father wants to mix a music clip with his family's vacation video as background music. 2. A disc jockey (DJ) wants to use two music clips to produce a new one to be used in a party.
3. A doctor inserts some new information in a patient's record, which is inspected by different doctors. 4. A user wants to recommend a movie to another friend so he/she clips the movie into one minute and sends it to his/her friend.
Three main subcategories of derivative rights have been defined [B. Rosenblatt, Digital Rights Management: Business and Technology, Hungry Minds Inc., U.S.], namely Extract where a part of the digital content is extracted to produce another digital content, Embed where two digital contents are mixed to produce a digital content and Edit where some features of the digital content are altered and a new version is produced.
In the first instance the father embeds the music clip into his own video clip and derivative rights of the music clip have been made. If the DRM system does not allow derivative rights, the father could not use the music clip in his personal video. In the second instance the DJ embeds two licensed (copyrighted) music clips generating a "new" derivative music clip. In the third instance the doctor edits the content of the patient's record and the digital rights may be altered resulting in a derivative patient record. In the last instance a part of the movie is extracted from the movie and a derivative short clip is produced.
From the content owners' perspective, the following problems can be caused by exercising the uncontrolled derivative rights:
1. Lost control of the derivative content:
When a user exercises the extract rights on the source content, the derivative content is produced. The derivative content may not be controlled by the license, which is associated to the source content. The usage of the derivative content is not confined, thus rights violation is bound to happen. For instance, the user can continuously exercise the extract rights and distribute the derivative content freely.
2. Rights conflicts of different licenses:
When a user exercises the embed rights on two source contents, which are controlled by two different licenses that may have different rights, conflicts of rights may occur e.g. due to different rights and state information. For instance, one of the contents can only be played twice, and the other can only be played once.
3. Revocation problem of derivative content:
Furthermore, severe problems may occur when a user decides to transfer a certain license and the associated digital content to another user because the derivative content is not really confined by the license of the source content. In other words, if the source license and the associated content are revoked by the owner, the derivative content can still be used.
In short, if the derivative rights are not managed properly or controlled, a user can easily cheat the rights enforcement.
OBJECT AND SUMMARY OF THE INVENTION
The object of this invention is to reduce at least one of the above-mentioned problems.
This is achieved by a method of generating derivative digital content from at least one piece of source content associated with a source license identifying rights related to said source content. Said license comprises a content key to be used for accessing said source content. The method of generating said derivate digital content comprises the step of creating at least one derivate license associated with said generated derivate digital content. The derivative license identifies the rights related to said derivative content, and the derivative license further comprises key information linking the derivate license to said content key of said source license, where said key is to be used when accessing said derivative content. Thereby it is possible for at user to make derivative digital content without the owner of the content loosing control of the derivative content, because the rights of the derivative content are defined by the rights of the source content. Thus, a dependency between the derivative content and the source content is established. This is achieved because the derivative license does not contain the content key and therefore needs to obtain and derive the derivative content key from the source license which contains the source content key using the key information. The user can therefore not access the derivative content if the owner of the content has revoked the source license. The owner therefore has control of all licenses and content including the derivative content. Furthermore, rights conflicts are avoided because the access to the derivative content is controlled by the source license which has up to date information about the usage rights. Finally, revocation problems of the derivative content are avoided when a user decides to transfer a certain license and the associated digital content or the derivative license and the associated derivative digital content to another user because the derivative content is now confined by the source license of the source content.
In another embodiment of the method described above, the derivative digital content has been generated by embedding source content associated with different source licenses, and said key information links said derivate license to said content key of each of said different source licenses. Each content key is to be used when accessing said derivative content. Thereby it is achieved that a user can embed source content with different source licenses, and the owner of the different source licenses does not loose control of the licenses, because the user need to obtain a content key from each source license in order to access the derivative content. The owner of one of the different source licenses can therefore prevent a user from using the derivative content by revocation of his/hers source license.
In another embodiment of the method described above each of said content keys are used in a key derivation function to generate a new key to be used when accessing said derivative content. This makes it possible to make a content key for the derivative digital content made by embedding different source content and at the same time make this content key dependent on the content key form the source licenses.
In another embodiment of the method described above, said derivative digital content has been generated by editing said source content. This makes it possible for a user to edit the source content or add additional content without the owner of the source content loosing control of the license. This is achieved because the new derivative content is still dependent of the source license and therefore needs to receive a content key from the source license. If the user wants to protect his/her additional content it is possible to add an additional license protecting the additional content. The derivative content would in this case be dependent of both the source license and the additional license.
The present invention further includes a method of accessing derivative digital content generated from at least one piece of source content, wherein said source content is associated with a source license identifying rights related to said source content and further comprises a content key to be used when accessing said source content. Said derivative content is associated with at least one derivate license. The method of accessing derivative content comprises the step of reading said derivative license, wherein said license identifies rights related to said derivative content and further comprises key information linking the derivate license to said content key of said source license. The method further comprises the step of reading said content key of said source license based on said key information in said derivative license where said content key is to be used when accessing said derivative content. Thereby it is possible for at user to access the derivative content without the owner of the source content loosing control of the derivative content and license. This is achieved because the owner of the source content can revoke the source license and the user of the derivative content can thereafter not access the derivative content.
In another embodiment of the method of accessing derivative digital content described above said derivative digital content has been generated by embedding source content associated with different source licenses, and said derivative license comprises key information linking the derivate license to said content key of each of said different source licenses, and each of said content keys are read and are to be used when accessing said derivative content. This ensures that a user can access derivative content made by embedding different digital content with different source license and the owners of the source licenses do not lose control of the licenses. This is achieved because the user needs to read the content key of each source license in order to access the derivative content. The owner of the source content can therefore revoke a source license in order to prevent a user from accessing the derivative content. In another embodiment of the method of accessing derivative digital content described above said content keys are used in a key derivation function to generate a new key to be used when accessing said derivative content. This makes it possible to access the derivative content using one content key. However, since this content key depends of the content key of the source license, the owner of the source content is still able to prevent the users' access to the derivative content.
In another embodiment of the method of accessing derivative digital content, when there is a conflict between said source licenses, then a set of rules defining how said conflicts must be handled is used when accessing said derivate content. Hereby rights conflicts between two source licenses could be avoided. This could e.g. be derivative content made by embedding two source contents with different usage rights, where the first license allows the user to access the first source content 5 times, and the second license allows the user to access the second source content 3 times. The set of rules could then define that the source license with the most restrict rights defines the usage rights of the derivative content. In this case the derivative content could only be accessed 3 times. The rights conflicts rules depend on the business model used in the method/system and could therefore be varied and fitted for a certain purpose.
Further, the invention relates to a computer-readable medium having stored therein instructions for causing a processing unit to execute a method as described above. The present invention also includes a device for generating derivative digital content generated from at least one piece of source content associated with a source license identifying rights related to said source content, and said license comprises a content key to be used for accessing said source content, said device comprising means for creating at least one derivate license, said derivative license identifying rights related to said derivative content and said derivative license further comprising key information linking the derivate license to said content key of said source license, where said key is to be used when accessing said derivative content; and means for associating said derivative license with said generated derivate digital content. The advantages achieved by the device are described above. The present invention also includes a derivative digital content generated from at least one piece of source content associated with a source license identifying rights related to said source content, and said license comprises a content key to be used when accessing said source content, where said derivative content is associated with at least one derivate license, and said device comprising means for reading said derivative license, wherein said license identifies rights related to said derivative content and further comprises key information linking the derivate license to said content key of said source license and means for reading said content key of said source license based on said key information in said derivative license where said content key is to be used when accessing said derivative content. The advantages achieved by the device are described above. The present invention also includes a computer data signal embodied in a carrier wave comprising a derivative license wherein said derivative license is associated to derivative digital content, said derivative content being generated from at least one piece of source content associated with a source license identifying rights related to said source content, and where said source license comprises a content key to be used when accessing said source content, said derivative license identifying rights related to said derivative content and further comprising key information linking the derivate license to said content key of said source license. Hereby the same advantages as described above are achieved, and furthermore it is possible to send and to control the rights of the derivative content in a network of devices. The present invention also includes a memory for storing data comprising a data structure describing a derivative license wherein said derivative license is associated to derivative digital content, where said derivative content is generated from at least one piece of source content associated with a source license identifying rights related to said source content, and where said source license comprises a content key to be used when accessing said source content, said derivative license identifying rights related to said derivative content and further comprising key information linking the derivate license to said content key of said source license. Hereby the same advantages as described above are achieved, and furthermore it is possible to store and to control the rights of the derivative content. BRIEF DESCRIPTION OF THE DRAWINGS
In the following preferred embodiments of the invention will be described referring to the figures, where Figure 1 illustrates an authorized domain of a DRM system in which the present invention is implemented.
Figure 2 illustrates the structure of a typical license and the structure of a derivative license introduced by the present invention.
Figure 3 illustrates what happens when a user extracts a part of a digital content and produces a derivate digital content.
Figure 4 illustrates what happens when a user embeds two pieces of digital content and produces a new derivative digital content.
Figure 5 illustrates what happens when a user edits an item and produces an edited derivative digital content.
DESCRIPTION OF PREFERRED EMBODIMENTS
Figure 1 illustrates an authorized domain of a DRM-system (100) comprising a number of devices, a DRM-server (101), a stereo (102), a monitor/TV/DVD player (103), a portable device (104), a personal computer (105), a wireless network comprising an antenna (106), a mobile phone (107) and a PDA (108). The devices are interconnected via a network (110), e.g. the Internet. The devices are able to play/render different types of digital content; a personal computer (105) could for instance use a software program; a stereo (102) could play a piece of music; a DVD player (103) could show a movie. Many of these digital contents are copyright protected, and the different devices therefore need to obtain a license in order to be able to play/render the digital content. The devises could e.g. obtain a license through the DRM-server (101) and thereby get access to the digital content. The DRM-server manages the licenses and the user rights of the digital content e.g. by issuing and revocating licenses. However, some users might alter the digital content and the corresponding license e.g. by extracting a part of the digital content and thereby produce a new digital content, embedding two digital contents into a new digital content or edit some features of the digital content and thereby produce a new version. The result is that the DRM-server could loose control and track of the derivative content. The present invention could be implemented in the above-described system and prevent the DRM-server from loosing control and track of derivative content. Figure 2 illustrates the structure of a typical source license (201) and the structure of a derivative license (202) introduced by the present invention. A license is associated with the digital content like software, music, movies, etc. and makes it possible for a DRM-system to manage and control copyright protected content, and it furthermore makes it possible for a device to render the digital content.
A typical license (201) may contain Metadata (203), which encapsulates some meta-data information about the content, user, etc.; Rights Information (204), which expresses the usage rights, terms and conditions, e.g. after a period of time the movie cannot be watched anymore; State Information (205), which captures the state information that restricts the rights; and Content Key (206), which is used to decrypt and then access the protected content.
In an authorized domain, the content key is encrypted using the domain key, which is shared among the devices in the authorized domain. Thereby, a device which belongs to the authorized domain can access the content. The states information (205) could e.g. be defined as an interval specifying a period of time during which the permissions can be exercised over the digital content; a count specifying the number of times the rights may be exercised over the digital content, an expiry specifying the time range, respectively the time limit for the rights or an accumulation specifying the maximum period of metered usage time during which the rights can be exercised (the accumulated state is decremented).
The structure of a derivative license (202) is shown to the right in Figure 2 and has metadata (203), rights information (204) and state information (205) like a typical license (201), but it does not contain the protected content encryption key (206) as a typical license does. However, a derivative license has some information about the protected content key which is used to protect the derivative content; this information is called key information
(207) which includes the location to obtain the source content key (206), etc. The derivative license is associated to the derivative content and is used when a device wants to render the content.
In order to explain how the invention should be implemented the following notation is used:
License {content Jd, rights _stats, keys/key Jnfo) to describe a license associated to the digital content identifier content Jd where content Jd is the digital content identifier; rights _stats is a list of rights information and corresponding state information, which could take the form of:
[{rights i, stats ι), (rightS2, stats 2), , (rightsn,statsn)]
keys are the protected content key(s) used to access the content. Note that a derivate license does not have the real key, but has keyjnfo, which is a structure:
key _info{contentn_id)
where contentn_id indicates that the key required to access the derivative content is from the license which is associated to the content with contentn_id.
Figure 3 illustrates what happens when a user extracts a part (302) of a source digital content, (301) and produces a derivate digital content (302').
Using the above introduced notation the digital content (301) has an associated license, which takes the following form:
License {content i_id, rights _states, keys)
A derivative license is generated to be associated to the derivative content (302') and the derivative license takes the following form:
License {content i_id', rights _states, key_info)
The derivative license inherits the rights information of the source license. Intuitively the process is similar to making a copy/replica of a license, where a digital content is copied and a new copy of license may be replicated to be associated to the newly copied content. The derivative license does not have the real key for decrypting the protected content. The derivative license contains the key information which may direct the DRM Client to the license, where the DRM Client could retrieve the required key:
key_info {contentijd) In other words, the derivative content (302) is also protected by using the same content key of the source content (301). Thereby, the problems of "lost control of the derivative content" and "revocation problem of the derivative content" can be solved. Consider this scenario: when the user illegally gives away the original content (301), the derivative content (302') cannot be used anymore because the license of the original content is revoked.
Figure 4 illustrates what happens when a user embeds two pieces of digital source content (401, 402) and produces a new derivative digital content (403').
The license of the first content (401) is License (content 401 Jd, rights _states 401, keyset), and the license of the second content (402) License (content 402 Jd, rights _states 402, keys 402)- The derivative license of the derivative content (403') is:
License (content403 _id, rights _states 403; key_infθ403-)
The newly derivative content is encrypted by using the combination of both keys from the licenses corresponding to content (401) and (402):
kev4o3' = f(kev4oi, key402)
The function f (ki,k2) is a key derivation function for generating a new key for protect-ting the derivative content. The function takes two different keys, namely ki and k2 to derive the new key. Thereby, the new key is related to both the keys. In practice, a one-way hash collision- free function can be used to generate a new unique key. Note that it is not required that the derivative license stores the new derived key for the derivative content. A strong dependency between the derivative license and the two source licenses could be achieved when the derivative license has the following key information which is required to generate the key for using the derivative content:
key_infθ403: = (content4oι_id , content 402 Jd)
When the user tries to access the derivative content using the DRM Client, the DRM Client retrieves the key information from the derivative license, locates the licenses corresponding to the key information and generates the key on-demand using the content keys stored on those licenses. The prior requirement is that the DRM Client must be acquainted to the key derivation function, which is reasonable. Thereby, if one of the licenses of the source content has been revoked due to e.g. illegal copying and distribution of the items, the derivative content cannot be further used. If the derivative content is used to further produce derivative content, the key derivation method can be further used to derive a new key for newly produced derivative content. For instance, if the derivative content (403') and source content (404) have been embedded to produce a new derivative content (405'), a new derivative license has been associated with the derivative content (405'):
LicensG(content405 _id, rights _states 405; keyjnfθ4os) where key_infθ405: = {content 401 Jd , content 404 Jd)
The content key for the derivative content (405') is:
kev4o5' = f(kev4o3', key404)
In other words, the derivative content access always depends on the source content due to the dependencies of the content keys. In order to render the derivate content (405') a device therefore needs to require an access key through the digital content (404) and the derivative content (403') and further back to source content (401) and (402).
Figure 5 illustrates what happens when a user edits a piece of source content (501) and produces an edited derivative digital content (501 '). A user editing an item is a distinct form of embedding an item because the user adds his/her own unlicensed content to the digital content. For instance, a user adds his/her personal (i.e., unlicensed) textual information in a report or the user adds his/her own personal music clip in a music piece. If the user wants to control other users' usage of his/her content, he/she can create an additional license for his/her personal content. The derivative rights are then generated as described in figure 4. However, if the user does not want to control other users' usage of his/her personal content, the rights of the usage rights of the new derivative content would be defined by the usage rights of the source content.
In order to prevent rights conflicts a set of rules defining how the different rights should be handled in case of conflicts could be implemented in the method/system. For instance, when two digital contents are embedded into a new digital content, the rights of the new digital content would depend on the rights of the two source digital contents. However, the rights of the two source digital contents could conflict e.g. by the amount of times the user is allowed to exercise the items. A rule defining which right defines the rights for the derivate content could then be introduced. This could e.g. be that the source content with the most restrict rights defines the rights for the derivate content. The rights conflicts rules depend on the business model used in the method/system and could therefore be varied and fitted for a certain purpose.
The above description describes how the present invention could be embodied and it must be understood that the invention is not limited to the embodiment described. The present invention may be changed, modified and further applied by those skilled in the art. Therefore, this invention is not limited to the details shown and described previously, but also includes all such changes and modifications within the scope of the appended claims and legal equivalents.