WO2007113163A1

WO2007113163A1 - Improved digital rights management for domains

Info

Publication number: WO2007113163A1
Application number: PCT/EP2007/052891
Authority: WO
Inventors: Christian GÜNTHER; Anja Jerichow
Original assignee: Siemens Aktiengesellschaft
Priority date: 2006-03-29
Filing date: 2007-03-27
Publication date: 2007-10-11

Abstract

According to the invention, a device, e.g. a mobile telephone, laptop computer, or PC, comprises a rights management agent (RMA), i.e. a program which receives rights objects as input and derives new, typically modified rights objects therefrom. The rights objects generated by an RMA are transmitted to other devices, e.g. a television or a music player. Devices receiving such a rights object can decode digital rights management (DRM)-protected data contents therewith without having to establish a data link to a rights issuer (RI) first. The RMA is protected against modifications of the mode of operation thereof to ensure that the method is reliable. Such protection can be obtained with the aid of trusted platform module (TPM) or universal integrated circuit card (UICC) technologies, for example.

Description

description

Improved digital rights management for groups of devices

The invention relates to a method, a

Rights management program and device for managing rights of use of electronic data objects for groups of devices.

With the help of Digital Rights Management (DRM) data content (eg still images, video and audio data, data for news, weather forecast and stock exchange services) protected against unauthorized access and their use by so-called rights of use (eg five times, twice transmitted) regulated become. Rights are assigned in the form of rights objects (RO) by a rights issuer (RI) and transmitted in cryptographically protected form by the RI to one or more user devices. The data content is initially available to the device only in encrypted form. With the help of a suitable rights object, the device can decrypt the data content.

The standardization body "Open Mobile Alliance" (OMA) not only defines DRM procedures in which a rights object is valid for a single device, but also procedures in which a rights object is valid for several end devices.These groups of devices are called domains A characteristic feature of the OMA DRM procedure for domains is that the copyright holder is responsible for managing such domains (eg adding new devices to an existing domain, removing devices from one domain, distributing rights objects to the members of a domain) every single device of a domain in the Be able to establish a data connection to the right holder - either directly or through another device. This raises a number of disadvantages for both the rightholder and the rights applicant: 1) Rightholders have a great deal of work to do with the

Management of device groups (domains) and when creating and distributing rights objects.

2) The right-acquirers want to be flexible and can pass on data content without much effort. 3) The rights buyers typically have devices that can actually connect to rights holders (e.g., cell phones, laptops, personal computers), as well as devices that often can not (e.g., TVs, music players). Even if all the devices of a user (direct or indirect) can establish data connections to right holders, it is inconvenient for the user to configure and set up these connections before the transfer of rights objects can take place. For the right purchaser this can result in additional connection costs.

Thus, the present invention has for its object to provide a method for managing rights of use of electronic data objects for groups of devices, which remedies these disadvantages, while equally taking into account the interests of rights holders and rights buyers.

According to the invention this object is achieved by a method, a rights management program and a device having the features specified in claims 1, 5 and 7. Advantageous developments of the present invention are specified in the dependent claims.

The present invention will be described below

Embodiments explained in more detail with reference to the drawings. It shows Figure 1 is a Digital Rights Management (DRM) method for

Groups of prior art devices,

Figure 2 is a Digital Rights Management (DRM) method for

Groups of devices according to the present invention.

Previous solution

OMA DRM

The OMA (Open Mobile Alliance) specifies digital rights management (DRM) procedures in which rights objects (ROs) are valid not only for individual devices but also for groups of devices (domains). However, each individual device must be able to establish a direct or indirect data connection to rights holders. With the help of DRM data content (eg still images, video and audio data, data for news, weather forecasts and stock exchange services) can be protected against unauthorized access and their use can be regulated by so-called rights (eg listen to five times), see [OMA DRM] and [OMA REL]. For this purpose, the data content is encrypted by the file content publisher (Content Issuer - CI) to protect it from unauthorized access 101.

Only those devices that have the appropriate cryptographic key can decrypt the data content. For this purpose, the user of the device must acquire a so-called rights object (RO) from the copyright holder RI, in which the cryptographic key in question is contained (together with an identification of the associated data content and a specification of the rights). The protocol used between the device and the RI will be described below. Among other relevant for the creation of such a rights object The CI sends this cryptographic key to the RI 102 for information.

Those cryptographic keys can not usually be transmitted to the device in unencrypted form, otherwise they can be intercepted and used by devices that do not have a corresponding RO. The cryptographic key itself must therefore be transmitted encrypted to the device. The OMA DRM specifications use public key procedures. In the case of a rights object that is valid only for a single device, the OMA DRM procedure works as follows:

1. The device is provided with a certificate that assigns the device identity to a public

Encryption key (a pair (m, e) of natural

Numbers) binds. The belonging private

Decryption key d (also a natural number) only knows the device. 2. The RI verifies the device certificate.

3. The rights holder RI generates a key REK (Rights Encryption Key), a key MK (Message authentication code Key) and a random number Z in the range between 0 and m-1. The key MK is used to protect the rights object from changes ,

4. The RI derives a key KEK (Key Encryption Key) from a Z using a hash function.

5. RI encrypts Z using public device key (m, e): Cl = ENCRYPT [m, e] (Z). 6. RI encrypts REK | MK, the concatenation of REK and

MK, with the help of KEK:

C2 = ENCRYPT [KEK] (REK | MK).

7. RI encrypts CEK (Content Encryption Key) using REK: C3 = ENCRYPT [REK] (CEK). CEK is the key that helps the data content

C is encoded: EncC = ENCRYPT [CEK] (C). 8. RI sends to the device a rights object (an XML file) containing, among other things, Cl, C2 and C3.

The encrypted data content EncC is typically not received by the device from the RI but via another device

Communication channel (e.g., download from a website, or as a file on a storage medium). The device now has the encrypted data content EncC and an associated rights object with the cryptographic data Cl, C2 and C3 available. To decrypt EncC, the device does the following:

9. The device decrypts Z using Cl and its private device key d: Z = DECRYPT [d] (Cl). 10. The device derives the key KEK from Z in the same way as the RI did in step 4 above.

11. Using KEK, the device decrypts the keys REK and MK: REK | MK = DECRYPT [KEK] (C2).

12. Using MK, the device checks whether the rights object is unchanged.

13. Using REK, the device decrypts the key CEK: CEK = DECRYPT [REK] (C3).

14. Based on the knowledge of CEK, the device can now decrypt the encoded data content EncC: C = DECRYPT [CEK] (EncC).

To set up a device domain, all devices that are to become members of the domain must first request their inclusion in a domain with the right holder (RI). For this, the devices must have a direct or indirect

Data connection to the RI. The rights holder then first distributes to all devices whose request has been accepted by the RI, a so-called domain key DK. This means that the RI generates DK and then performs the following steps for each device in the domain:

1. The device is provided with a certificate that assigns the device identity to a public Encryption key (a pair (m, e) of natural numbers) binds. The belonging private

3. The rights holder RI generates a key MK (Message authentication code Key) and a random number Z in

Range between 0 and m - 1. The MK key is used to protect the message that KD transports to the device.

5. RI encrypts Z using public device key (m, e): Cl = ENCRYPT [m, e] (Z). 6. RI encrypts DK | MK, the concatenation of DK and MK, with the help of KEK: C2 = ENCRYPT [KEK] (DK | MK).

7. RI sends to the device a rights object containing, among other things, Cl and C2. With the help of Cl and C2, each device of the domain is now able to perform the following steps to decrypt the domain key DK:

8. The device decrypts Z using Cl and its private device key d: Z = DECRYPT [d] (Cl). 9. The device derives the key KEK from Z in the same way as the RI did in step 4 above.

10. With the help of KEK the device decrypts the keys DK and MK: DK | MK = DECRYPT [KEK] (C2).

11. Using MK, the device checks if the message is unchanged.

In order for the devices of the domain to be able to decrypt a particular data content C that is encrypted using a Content Encryption Key (CEK) (EncC), the RI performs the following steps: 12. RI generates two keys REK and MK '.

13. RI encrypts REK | MK 'with the help of DK: C3 = ENCRYPT [DK] (REK I MK'). 14. RI encrypts CEK using REK: C4 = ENCRYPT [REK] (CEK).

15. RI sends a rights object to at least one of the devices in the domain, including C3 and C4. Other devices can get this RO in a different way.

Since DK is only known to the members of the domain, only these can decrypt the key CEK. This is done as follows: 16. Each device decrypts REK and MK 'using DK: REK I MK' = DECRYPT [DK] (C3).

17. Each device checks with the help of MK 'that the rights object is unchanged.

18. Each device uses REK to decrypt the key CEK: CEK = DECRYPT [REK] (C4).

Based on the knowledge of CEK, each device can now decrypt the encoded data content EncC: C = DECRYPT [CEK] (EncC).

If data is passed on to non-members of a domain (so-called superdistribution) 105, then the new owner of the encrypted data has to request an RO at the RI 106 using the same procedure as described for 103.

Solution According to the Invention A device (e.g., cell phone, laptop, PC) is equipped with a

"Rights Management Agent" (RMA), i.e., a program that receives as input rights objects and derives new, typically modified rights objects, a device with RMA shall be called "RMA device".

The rights objects generated by an RMA are transmitted to other devices (e.g., TV, music player). Devices that receive such a rights object can use it to decrypt DRM-protected file holds without first having to

To establish a data connection to a Rights Issuer (RI). The RMA is against changes in his Function protected to ensure the safety of the process. Such protection can be achieved, for example, using Trusted Platform Modules (TPM) or Universal Integrated Circuit Card (UICC) technologies.

Figure 2 shows a typical embodiment of this invention. A laptop is equipped with an RMA program, the functionality of which is protected against change by means of a Trusted Platform Module (TPM). The user of the laptop would like to listen to a particular DRM protected piece of music on a music player. For this, the laptop asks the desired piece of music at the CI 201 and downloads the encrypted piece of music from a server 202. Subsequently, the piece of music is encrypted passed to the music player 203. The DRM-protected

Music can be listened to only with the help of an appropriate rights object containing the correct decryption key, along with the rights the user wants (for example, listen to five times). Therefore, the laptop, which has a suitable data connection to the right holder, requests from the latter such a rights object 204. The rights holder makes this rights object RO available to the laptop 205 (and typically charges the user). The TPM-protected RMA program on the laptop derives from the rights object RO a rights object RO 'for the music player. Contains RO the

Decryption key CEK and, for example, the right "listen five times", then the rights object RO 'could also contain the key CEK and the derived right "three times". The laptop sends the derived rights object RO 'to the music player 206. The RMA program modifies the original rights object RO by reducing the rights contained therein to "listen twice." With RO', the music player can decrypt the encrypted piece of music Play user three times, unlike the OMA DRM method for domains, the method described here thus does not require a data connection between rights holder and music player, via which the player obtains a rights object.

This embodiment can be varied in many ways:

1. The protection of the RMA program can not only be achieved by means of Trusted Platform Module (TPM) technologies, but also e.g. using Universal Integrated Circuit Card (UICC) technologies.

2. The RMA program and other data relevant to the functioning of the RMA can either

• transferred to the device or the chip card and activated during the manufacture of the device or the chip card

(i.e., the user can use the services of the RMA immediately), or

• transferred to the device or the chip card during the production of the device or the chip card, but only activated later (for example by the user if necessary), or

• are not yet transferred to the device or the chip card during the production of the device or the chip card, but are only loaded and activated at a later time (for example by the user if necessary) onto the device or the chip card ,

3. Of course, the type of data content is not limited to pieces of music. This invention is applicable to all types of data contents that can be protected by DRM techniques: audio data, video data, mobile television data, still images, office documents, texts, intelligence data, weather services, stock exchange services, etc.

4. In the context of this invention, it is irrelevant how the DRM-protected data content to the display device (the

Music player in Figure 2): In Figure 2, the DRM-protected data content was loaded from the RMA device and sent to the Presentation device forwarded. The DRM-protected data content can just as easily be made available to the presentation device via a fixed storage medium (eg CD, DVD, USB stick) or transmitted from another device via a wired or wireless connection to the presentation device. 5. The connection between the RMA device and the presentation device for the transmission of rights objects can be both wired and wireless. RMA device and display device need not be directly connected to each other, but can also communicate with each other via one or more intermediate devices.

In order to reduce the effort for the generation and transmission of rights objects for rightholders, these tasks are at least partially taken over by devices on the user side. In the context of this invention, these tasks are taken over by the RMA. In this way, the present invention increases user-friendliness by allowing the user to display data content on devices that have no communication link to rights holders. Here, however, there is a security issue: Rightsholders can not trust unprotected RMA programs whose functionality can easily be changed by the user in their favor. Therefore, this invention involves special protection of the RMA program, e.g. with the help of TPM or UICC technologies. The following describes these two protections:

TPM protection mechanisms

The Trusted Platform Module (TPM) is a chip that is firmly bound to a device (such as the motherboard of the PC, mobile phone, or other device) and has technical control mechanisms for the correct execution of

Programs or access to data. TPM is part of the TCG specifications [TCG TPM] provided by the TCG (Trusted Computing Group). TCG is an international, industry-driven standardization consortium that specifies open standards for trusted computing (see http://www.trustedcomputinggroup.org) Also part of TCG's security mechanisms is CRTM (Core Root of Trust Measurement), a bios extension to the CRTM is an executable code for measuring individual system states outside the TPM and the results are then stored within the TPM.

The following security mechanisms are provided by a TPM:

1. Keys and certificates can be generated by the TPM and stored securely next to passwords in the TPM. The TPM can sign data objects, verify signatures, as well as encrypt and decrypt. It is important that private keys that are generated in the TPM remain protected even when they are used in the TPM.

2. The authenticity of a TPM is verifiable on the basis of an endorsement certificate in which the manufacturer of the TPM confirms whether the TPM installed by him and the associated public key comply with the TCG specification.

3. TPM provides a measurement process that ensures the integrity of the platform. The measured by CRTM

System states are stored in the Platform Control Register (PCR) and allow verification of hardware integrity by generating hash values about the system state. Each modification calls a hash function with the chained old and new values. The Attestation Identity Key (AIK), an asymmetric key used by a user to prove the identity of their device to the outside, can only be used if the PCR value provides the same result as at the time of AIK generation.

Universal Integrated Circuit Cards (UICC) protection mechanisms In UMTS mobile phones, user-specific data (eg user identity, secret key for network access) is known to be stored on small chip cards which the user receives from the operator of a mobile radio network. These chip cards are called Universal Integrated Circuit Cards (UICC). The functions that operate on this data are implemented by a program (UICC application) stored on the UICC called the Universal Subscriber Identity Module (USIM). Both the data and the USIM operating on this data are protected against unauthorized reading and modification.

These protections have been specified by the European Telecommunications Standards Institute (ETSI) for UICCs [ETSI TS 102221]. They contain rules that specify under which conditions commands such as READ or UPDATE on data or programs stored on the UICC. Based on [ETSI TS 102221], the 3GPP standardization body responsible for UMTS has the interface between UICC and the actual one

Mobile device (ie mobile phone without UICC) specified [3GPP TS 31.101]. Within the scope of this invention, the rights management agent (RMA) can be implemented as a UICC application and protected against unauthorized alteration or read-out with the protection mechanisms defined by ETSI and 3GPP. Modern UICCs offer sufficient memory (in the MegaByte range). In addition, UMTS UICC applications do not necessarily have to be stored on their production on the UICCs, but can also be retrofitted by the operator of the USIM mobile network. In GSM networks, the known Subscriber Identity Modules (SIM) are used instead of USIM applications on UICCs. Although these provide similar protection mechanisms as UICCs [3GPP TS 11.11], they are less suitable for the technical realization of this invention, since they have limited storage space (in the kilobyte range).

The present invention has, for example, the following advantages:

• For rightholders, the overhead of managing DRM device domains and generating and distributing rights objects is reduced. If a rights holder still has to manage each individual device domain according to the current OMA DRM specifications, these tasks are performed in the

Within the scope of the present invention of

Rights Management Agents (RMAs) have been taken over to a significant extent or even made superfluous.

• Even devices that are unable to establish connections to right holders can easily be supplied with rights objects by the RMA. This broadens the range of devices that can display DRM-protected data content, increasing revenue from DRM-protected data content.

• For users, DRM-protected data content becomes more attractive as it allows them to display it flexibly and without much effort on different devices. • Rightholders can have confidence in the security of the

Have procedures, as RMA programs behave according to their requirements (protection against changes to RMA programs by eg TPM or UICC technologies).

bibliography

[3GPP TS 11.11] 3GPP, Specification of the Subscriber Identity Modules - Mobile Equipment (SIM - ME) Interface, Release 1999, 2005-06.

[3GPP TS 31.101] 3GPP, UICC - Terminal Interface, Physical and Logical Characteristics, Release 6, 2005-06.

[ETSI TS 102221] ETSI, Smart cards; UICC - Terminal Interface; Physical and Logical Characteristics, Release 7, 2005-05.

[OMA DRM] Open Mobile Alliance, DRM Specification, Approved Version 2.0, 2006-03-03.

[OMA REL] Open Mobile Alliance, DRM Rights Expression Language, Approved Version 2.0, 2006-03-03.

[TCG TPM] TCG, Trusted Platform Modules (TPM) Specifications.

acronyms

3GPP Third Generation Partnership Project

(Standards body)

CEK data content encryption key (Content Encryption Key)

DRM Digital Rights Management ETSI European Telecommunication Standards Institute

(Standards body)

KEK key encryption key (Key Encryption

Key)

OMA Open Mobile Alliance (standardization committee)

REK Rights Encryption Key (Rights Encryption

Key)

REL Rights Expression Language (Rights Expression

Save

RI Rightsholders

RMA Rights Management Agent

RO rights object

SIM Subscriber Identity Module

TCG Trusted Computing Group (Standardization Board) TPM Trusted Platform Module

UICC Universal Integrated Circuit Card UMTS Universal Mobile Telecommunication System

Claims

claims

1. A method for managing rights of use of electronic data objects for groups of devices, wherein - the rights of use to an electronic data object by a right holder predetermined use forms and are summarized in a first rights object,

a second rights object is derived from the first rights object by a rights management unit on a first device, which at least comprises a subset of the usage rights from the first rights object,

- The integrity of the rights management unit is protected by a security module of the first device.

2. The method of claim 1, wherein the security module is a TPM (Trusted Platform Module) module of the first device or a UICC (Universal Circuit Card) based module of the first device.

3. The method of claim 1, wherein

the second rights object is transmitted from the first device to a second device,

- An electronic data object can be used by the second device depending on the rights of use encompassed by the second rights object.

4. The method of claim 1, wherein

The electronic data object and / or the second rights object can be made available to the second device via a fixed storage medium (for example CD, DVD, USB stick) or transmitted to the second device from another device via a wired or wireless connection.

5. Rights management program on a device for deriving a second rights object from a first rights object, wherein the first rights object comprises usage rights to an electronic data object which describe usage forms specified by a copyright owner,

the second rights object comprises at least a subset of the usage rights from the first rights object,

- the integrity of the rights management program is protected by a security module of the device.

The rights management program of claim 5, wherein the security module is a TPM (Trusted Platform Module) module or is a UICC (Universal Circuit Card) based module.

7. Device with a security module and a rights management unit for deriving a second

Rights object from a first rights object, each of which includes rights of use in dependence of which an electronic data object is usable, wherein the integrity of the rights management program is protected by the security module of the device.

The device of claim 7, wherein the security module is a TPM (Trusted Platform Module) module or is a UICC (Universal Circuit Card) based module.