Abstract:
The present invention discloses several methods to strengthen the integrity of entities, messages, and processing related to content distribution as defined by the Open Mobile Alliance (OMA) Digital Rights Management (DRM). The methods use techniques related to the Trusted Computing Group (TCG) specifications. A first embodiment uses TCG techniques to verify platform and DRM software integrity or trustworthiness, both with and without modifications to the DRM rights object acquisition protocol (ROAP) and DRM content format specifications. A second embodiment uses TCG techniques to strengthen the integrity of ROAP messages, constituent information, and processing without changing the existing ROAP protocol. A third embodiment uses TCG techniques to strengthen the integrity of the ROAP messages, information, and processing with some changes to the existing ROAP protocol.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Patent Application No. 60/798,152 filed May 5, 2006, which is incorporated by reference as if fully set forth herein. 
    
    
     FIELD OF INVENTION 
     The present invention generally relates to digital rights management (DRM) methods in wireless communication networks. More particularly, the present invention provides methods for enhancing security, integrity, and trustworthiness in systems operating in accordance with the Open Mobile Alliance (OMA) DRM specifications. 
     BACKGROUND 
     The OMA DRM is a DRM system specified by the OMA, a consortium of mobile phone and device manufacturers and mobile service providers. The scheme is implemented on many mobile phones and is intended to be used by mobile content providers to add DRM to their products and services. Two versions of the OMA DRM have been released: OMA DRM 1.0 and OMA DRM 2.0. 
     OMA DRM 1.0 addressed schemes for basic management of digital rights for content objects. As such, it did not provide strong protection for either the content object or the rights object. OMA DRM 1.0 specifies three methods of delivery: Forward Lock (which prevents the user from forwarding content to other users or devices), Combined Delivery (a combined rights object and media object), and Separate Delivery (separate rights object and media object). The OMA DRM 1.0 was designed to handle small-sized media objects such as ring tones or wallpapers for phones. 
     OMA DRM 2.0 improves and extends the OMA DRM 1.0 delivery mechanism. A device compliant with OMA DRM 2.0 has an individual certificate based on a DRM public key infrastructure (PKI), i.e., each device has a public key, a corresponding private key, and a certificate verifying this fact. Each rights object (RO) is protected for both confidentiality (by encryption) and integrity (by digital signatures). The use of PKI, encryption, and integrity checking strengthens the security of the OMA DRM 2.0 system compared to that of the OMA DRM 1.0 system. 
     OMA DRM 2.0 also specifies a set of protocols that together are called the Rights Object Acquisition Protocol (ROAP) that comprises various sub-protocols related to mutual authentication and registration between a device and a rights issuer (RI), requesting ROs, response to delivery of ROs or refusal to deliver ROs, and joining and leaving of domains by the device. 
     The following are some of the main entities defined in the OMA DRM: 
     Actor—An actor is an external entity that carries out use cases. 
     Backup/Remote Storage—Transferring ROs and Content Objects (COs) to another location with the intention of transferring them back to the original device. 
     Combined Delivery—A OMA DRM 1.0 method for delivering protected content and the RO. The RO and the protected content are delivered together in a single entity, the DRM message. 
     Confidentiality—The property that information is not made available or disclosed to unauthorized individuals, entities, or processes. 
     Composite Object—A CO containing one or more media objects by means of inclusion. 
     Connected Device—A device capable of directly connecting to an RI using an appropriate protocol over an appropriate wide area transport/network layer interface. 
     Content—One or more media objects. 
     Content Issuer (CI)—The entity making content available to the DRM agent. 
     Content Provider—An entity that is either a CI or an RI. 
     Device—A user equipment with a DRM agent. It can be either a connected device or an unconnected device, but this distinction is contextual and variable in nature, since a connected device can become an unconnected device when it loses its capability to directly connect to an RI. 
     Device Revocation—The process of an RI indicating that a device is no longer trusted to acquire ROs. 
     Device RO—An RO dedicated for a particular device by means of the device&#39;s public key. 
     Domain—A set of devices, which are able to share domain ROs. Devices in a domain share a domain key. A domain is defined and managed by an RI. 
     Domain Identifier—A unique string identifier of the domain key. 
     Domain Key—A 128 bit symmetric cipher key. 
     DRM Agent—The entity in the device that manages permissions for media objects on the device. 
     DRM Content—Media objects that are consumed according to a set of permissions in an RO. 
     DRM Time—A secure, non-user changeable time source. The DRM time is in the UTC time format. 
     Integrity—The property that data has not been altered or destroyed in an unauthorized manner. 
     Join Domain—The process of an RI including a device in a domain. 
     Leave (De-Join) Domain—The process of an RI excluding a non-revoked device from a domain. 
     Media Object—A digital work or a composite object. 
     Network Service Provider—The entity providing network connectivity for a mobile device. 
     Permission—Actual usages or activities allowed by the RI over DRM content. 
     Play—To create a transient, perceivable rendition of a resource. 
     Protected Content—Media objects that are consumed according to a set of permissions in an RO. 
     Restore—Transferring the protected content and/or ROs from an external location back to the device from which they were backed up. 
     Revoke—Process of declaring a device or RI certificate as invalid. 
     Rights Issuer (RI)—An entity that issues ROs to OMA DRM conformant devices. 
     RI Context—Information that was negotiated with a given RI during the 4-pass Registration Protocol such as RI ID, RI certificate chain, version, algorithms, and other information. An RI Context is necessary for a device to successfully participate in all the protocols of the ROAP suite, except the Registration Protocol. 
     Rights Object (RO)—A collection of permissions and other attributes which are linked to protected content. 
     Rights Object Acquisition Protocol (ROAP)—A protocol that enables devices to request and acquire ROs from an RI. 
     ROAP Trigger—An extensible markup language (XML) document including a URL that, when received by the device, initiates the ROAP. 
     Stateless Rights—ROs for which the device does not have to maintain state information. 
     Stateful Rights—ROs for which the device has to explicitly maintain state information, so that the constraints and permissions expressed in the RO can be enforced correctly. An RO containing any of the following constraints or permissions is considered Stateful Rights: &lt;interval&gt;, &lt;count&gt;, &lt;timed-count&gt;, &lt;datetime&gt;, &lt;accumulated&gt; or &lt;export&gt;. 
     Super-Distribution—A mechanism that (1) allows a user to distribute protected content to other devices through potentially insecure channels and (2) enables the user of that device to obtain an RO for the super-distributed protected content. 
     Unconnected Device—A device that is capable of connecting to an RI via a connected device using an appropriate protocol over a local connectivity technology, e.g., OBEX over IrDA (object exchange over infrared), Bluetooth, or Universal Serial Bus (USB). An unconnected device may support DRM Time. 
     User—The human user of a device. The user does not necessarily own the device. 
       FIG. 1  is an overview of the existing OMA DRM 2.0 functional architecture  100 . The architecture  100  consists of a DRM system  102 , a content provider  104 , and a user  106 . The DRM system  102  includes a CI  110 , an RI  112 , DRM agents  114 , a network store  116 , and removable media  118 . The CI  110  distributes protected content  122  and the RI  112  distributes an RO  124 . The DRM agents  114  redistribute the protected content  122 . 
     The CI  110  is an entity that delivers DRM content  122 . The OMA DRM defines the format of the DRM content  122  to be delivered to DRM agents  114  and the way that the DRM content  122  can be transported from the CI  110  to the DRM agent  114  using different transport mechanisms. The CI  110  may do the actual packaging of the DRM content  122  itself or it may receive pre-packaged content from some other source. 
     The RI  112  is an entity that assigns permissions and constraints to the DRM content  122  and generates ROs  124 . An RO  124  is an XML document expressing permissions and constraints associated with the DRM content  122 . ROs  124  govern how the DRM content  122  may be used; the DRM content  122  cannot be used without an associated RO  124  and may only be used as specified by its associated RO(s). DRM content could be associated with more than one RO if, for example, the RO has a time expiration (e.g., 10 days), and after the time expiration a new RO would be needed to access the content. 
     The DRM agent  114  is a logical entity that is responsible for managing point-of-consumption enforcement of the DRM content  122 . The DRM agent  114  embodies a trusted component of a device, and is responsible for enforcing the permissions and constraints for the DRM content  122  on the device, controlling access to the DRM content on the device (which can only be accessed through the DRM agent  114 ), and so on. 
     The DRM content  122  is packaged to protect it from unauthorized access before it is delivered. The CI  110  delivers the DRM content  122 , and the RI  112  generates the RO  124 . The CI  110  and the RI  112  embody logical roles, rather than physical entities, in the system  102 . For example, in one deployment, content owners may pre-package DRM content, which is then distributed by a content distributor acting as both CI and RI. 
     An RO  124  governs how the DRM content  122  may be used. DRM content  122  cannot be used without an associated RO  124 , and may only be used according to the permissions and constraints specified in the RO  124 . The OMA DRM makes a logical separation of DRM content from ROs. DRM content and ROs may be requested separately or together, and they may be delivered separately or at the same time. When they are delivered at the same time, they are typically both provided by the CI  110 , with the RO and the content embedded in a DRM Content Format (DCF). 
     An RO  124  is cryptographically bound to a specific DRM agent  114  by a set of keys, so only that specific DRM agent  114  can access it. The DRM content  122  can only be accessed with a valid RO  124 , so the content  122  can be freely distributed or super-distributed. 
     The OMA DRM 2.0 allows one RO to be bound to a group of DRM agents. Such a group is called a domain. DRM content and ROs distributed to a domain may be shared and accessed offline by all DRM agents belonging to that domain. For example, a user may purchase DRM content for use on both her phone and her PDA. 
     The OMA DRM specifications define the format and the protection mechanism for DRM content (or the DCF), the format (rights expression language (REL)) and the protection mechanism for the RO, and the security model for management of encryption keys. The OMA DRM specifications also define how the DRM content and the ROs may be transported to devices using a range of transport mechanisms, including pull (HTTP pull, OMA download), push (WAP push, MMS), and streaming. However, the OMA DRM specifications do not address any interaction between network entities, e.g., between the CI  110  and the RI  112 . 
     The following is a non-exhaustive list of the use cases covered by the OMA DRM 2.0 specifications. 
     1. Basic Pull Model 
     A user selects content to download by browsing to a Web site, and confirms the terms of the purchase. The CI  110  identifies and protects the content  122 , i.e., packages it. The content  122  is encrypted using the content encryption key (CEK). The device capabilities can be detected using advertised MIME-type support, etc. The RI  112  generates an RO  124  for the content  122  and the target DRM agent  114 . The RO  124  includes the permissions for the content transaction and the CEK. Lastly, the RO  124  is cryptographically protected by encryption (using an RO encryption key, or REK) and digital signatures, and is bound only to the target DRM agent  114 . The DRM content  122  and the protected RO  124  are then delivered to the DRM agent  114 . 
     2. Push of DRM Content 
     An alternative distribution model is to push the content directly to a device using Multimedia Messaging Service (MMS), WAP Push, or a similar method, without a preceding discovery process. There are two variations on this use case. 
     2A. Content Push 
     The CI  110  and/or the RI  112  may have certain prior knowledge of a user and a particular DRM agent  114 , so that the content  122  and an RO  124  can be formatted and packaged for delivery. 
     2B. Push-Initiated Pull 
     In this case, the CI  110  and/or the RI  112  may have no prior knowledge about the user or their DRM agent  114 , but may still wish to deliver content, e.g., to allow the user to preview the content  122  to entice them to purchase the content. Instead of pushing the DRM content  122  directly to a user, a link to the content or a link to the preview of the content can be sent. Following the link will take the user to a specific location and then the procedure continues as in the basic pull model. 
     3. Streaming of DRM Content 
     Both the basic pull and the push use cases assume that the content is packaged and delivered in its entirety. Alternatively, the content may be packetized and delivered as a stream. In this case, the stream itself is protected (encrypted). The exact format of the encryption has been left out of the scope of OMA DRM, and can be chosen from existing encryption standards. The streams may be protected with encryption schemes which are different from those specified by OMA for download, to address possible packet loss, etc. After the stream is encrypted, though, access to the stream can be controlled through the same procedure as described earlier for discrete content. An RO is generated, the stream encryption key is put in the RO just like a CEK would be, and the RO is then cryptographically bound to a DRM agent. 
     4. Domains 
     Domains are an optional feature and may not be supported by all RIs. Domains expand the basic model of the OMA DRM 2.0 where the ROs and the CEK are bound to a specific DRM agent  114 , and allow an RI  112  to bind rights and CEKs to a group of DRM agents instead of just a single DRM agent. Users may then share the DRM content  122  off-line between all DRM agents belonging to the same domain. An RI  112  may use the domain concept to provide new services, such as enabling users to access DRM content  122  from several devices that they own or provide support for unconnected devices where users purchase the DRM content and rights via one device (e.g., a PC) for later use on another device (e.g., a portable player). 
     5. Back-Up 
     The DRM content  122  can be stored on removable media  118 , in a network store  116 , or in some other form of storage. The DRM content  122  is stored in encrypted form and can only be accessed by a particular target DRM agent  114  using an associated RO  124 . ROs  124  can be stored for backup purposes if the RO only contains stateless permissions. The security model ensures that the RO  124  is protected and can only be accessed by the intended DRM agent  114 , even if the RO  124  is stored off-device. Some permissions require maintenance of state by the DRM agent  114 , e.g., a limited number of plays. Such ROs cannot be stored off-device, as this might result in loss of the state information. 
     6. Super-Distribution 
     The DRM content  122  can be copied and transferred to other DRM agents  114 , e.g., a user sending the DRM content  122  to a friend. The friend, in order to access the content  122 , is taken to the RI  112  via a link in the DRM content package to acquire an RO  124 . 
     7. Export (to Non-OMA DRM Systems) 
     The DRM content  122  may be exported to other DRM systems, for use on devices that are not OMA DRM compliant, but support some other DRM mechanism. The OMA DRM architecture allows RIs  112  to, if they wish, express permission for DRM agents  114  to perform conversions to specific other DRM systems, possibly as specified by the other DRM system. The RI  112  may limit the export only to specific external DRM systems. 
     8. Support of Unconnected Devices 
     The OMA DRM enables a connected device to act as an intermediary to assist an unconnected device to purchase and download content  122  and ROs  124 . A user, for example, may have an OMA DRM compliant portable device (an unconnected device) that has no network connectivity, and an OMA DRM compliant mobile device (a connected device) that has network connectivity. After using the connected device to browse and purchase the DRM content  122  and downloading the DRM content  122  to the connected device, the user then may wish to play the DRM content  122  on the unconnected device. In this case, the DRM agent  114  on the connected device requests and downloads a domain RO  124  from the RI  112 . 
     The DRM agent  114  on the connected device then embeds the domain RO  124  in the DCF. The DCF can then be transferred to the unconnected device using an appropriate protocol over a local connectivity technology, e.g., Bluetooth or USB. Both the connected device and unconnected device must be OMA DRM compliant to support this functionality. Also, the unconnected device must belong to the same domain as the connected device. 
     Security and Trust 
     The following is an overview of the OMA DRM 2.0 security and trust measures. In general, any DRM solution needs to meet two security requirements: (1) the protected content must only be accessed by properly authenticated and authorized DRM agents; and (2) permissions on the protected content must be honored by all DRM agents. Enforcement of the permissions and constraints associated with the DRM content are the main concern of the security and trust measures of any DRM scheme. Unauthorized access to DRM content beyond what is stipulated by the associated RO and creation of illegal copies and redistribution of DRM content constitute the main threats to any DRM system. 
     The OMA DRM system provides the means for the secure distribution and management of protected content in the OMA environment and meets the requirements specified above. The OMA DRM enforces the use and protection of the content and the ROs at the point of consumption by using a DRM agent that ensures protected use of content under the constraints of the ROs. 
     The basic steps for distributing DRM content can be summarized as follows: 
     1. Content packaging. Content is packaged in a secure content container (DCF). The DRM content is encrypted with a symmetric content encryption key (CEK). The content can be pre-packaged, i.e., content packaging does not have to happen on the fly. The same CEK is not used for all instances of a piece of content, although this is not a requirement in the OMA DRM. 
     2. DRM agent authentication. All DRM agents have a unique private/public key pair and a certificate. The certificate includes additional information such as device maker, device type, software version, serial numbers, etc. This allows the CIs and the RIs to securely authenticate a DRM agent. 
     3. RO generation. The RO contains the CEK, which ensures that the DRM content cannot be used without an associated RO. ROs are made up of permissions (e.g., play, display, and execute) and constraints (e.g., play for a month, display ten times). ROs may also include constraints that require a certain user to be present (e.g., determined by a user identity) when the content is accessed. These permissions and constraints, along with other information embodied in the RO (e.g., copyright information), may be presented to the user. 
     4. RO protection. Before delivering the RO, sensitive portions of the RO (such as the CEK) are encrypted with a rights encryption key (REK), and the RO is then cryptographically bound to the target DRM agent. This ensures that only the target DRM agent can access the RO, the CEK, and the DRM content. In addition, the RI digitally signs the RO. The RO also governs access to the DRM content by including the CEK. The OMA DRM Rights Expression Language (REL) specifies the syntax (XML) and semantics of permissions and constraints governing the use of the DRM content. An RO has its own MIME content type. 
     5. Delivery. The RO and the DCF can now be delivered to the target DRM agent. Since both items are inherently secure, they can be delivered using any transport mechanism (e.g., HTTP/WSP, WAP Push, MMS). The RO and the DCF can be delivered together, e.g., in a MIME multipart message or can be delivered separately. 
     The OMA DRM trust model for the ROs is based on the public key infrastructure (PKI), whereby there are groups of principals, verifiers and one or more authentication authorities recognized and trusted by both. A single entity can play both as a principal and a verifier depending on the needs of the context and solutions chosen. The PKI enables a verifier to authenticate the identity and other attributes of a principal when they communicate over an open, unsecured network. In such a system, typically, the verifier does not have to maintain any sensitive information about the principals it interacts with, for the purposes of authentication. In addition, the Certification Authority (CA) is not directly involved in transactions between principal and the verifier. An RI trusts a DRM agent to behave correctly if the DRM agent&#39;s certificate is verifiable by the RI and has not been revoked. Similarly, a DRM agent trusts an RI to behave correctly if the RI&#39;s certificate is verifiable by the DRM agent and has not been revoked. 
     The primary entities of the PKI as applied to the OMA DRM are the CAs, the devices, and the RIs. The authentication and key transfer protocols of the OMA DRM require the RI to be able to authenticate the device and the device to be able to authenticate the RI. Such mutual authentication is accomplished by the ROAP. 
     In addition, devices are assumed to be provisioned (either at manufacturing time or later) with device public and private keys and associated certificates signed by an appropriate CA. Based on the certificate preferences expressed by the RI, the device has to provide an appropriate certificate. Devices are required to store the private keys in local storage with integrity and confidentiality protection. 
     The RIs are also provided with public keys, private keys, and certificates signed by a CA. The certificate chain (a chain of multiple certificates including the certificate of the public key owner signed by one CA and zero or more additional certificates of CAs signed by other CAs) is presented to the device at the time of the authentication protocol for validation of the certificate chain of trust. 
     It is noted that multiple CAs may exist in the DRM system. The ROAP protocol requires that the CA signing the RI certificates runs an Online Certification Status Protocol (OCSP) responder for use during the execution of the protocol. The CAs are also required to define the appropriate certificate policies to govern the use of the issued certificates. 
     The following describes the main aspects of OMA DRM security. 
     1. Confidentiality, which ensures that data is not accessible by an unauthorized party. As stated above, the protected content must only be accessible by properly authenticated and authorized DRM agents. To achieve this goal, protected content is encrypted. Encryption keys are unique to each media object, and ROs carry the encryption keys wrapped in keys only accessible by the intended recipients. 
     2. Authentication, which is the process by which a party identifies itself to another party. In the OMA DRM, mutual DRM agent and RI authentication is achieved in the 4-pass Registration Protocol, the 2-pass RO Acquisition Protocol, and the 2-pass Join Domain protocol. Depending on the protocol used and the message sent, authentication is achieved either through digital signatures on nonces or on time stamps. The 1-pass RO Acquisition Protocol achieves RI authentication through the digital signature on a time stamp. It does not authenticate the DRM agent to the RI, but due to the protected content being wrapped with the recipient&#39;s public key, authentication is done indirectly through key binding. The 2-pass Leave Domain Protocol authenticates the DRM agent to the RI through the digital signature on a time stamp. It does not authenticate the RI to the DRM agent. RIs are required to authenticate themselves to the DRM agent during delivery of ROs. This provides some level of assurance about the authenticity of the RI. 
     3. Data Integrity Protection ensures the ability to detect unauthorized modification of data. In the OMA DRM, data integrity protection, when applicable, is achieved through digital signatures on ROAP messages and ROs. 
     4. Key Confirmation ensures the recipient of a message containing a protected key that the message sender knows the key value. In the DRM context, this property protects against unauthorized re-issuance of ROs from one RI by another. In the OMA DRM system, key confirmation is achieved through a medium access control (MAC) over the protected key and the sending party&#39;s identity by using parts of the protected key as the MAC key. 
     The DRM agent has to be trusted by the RI, both in terms of correct behavior and in terms of a secure implementation. In the OMA DRM, each DRM agent is provisioned with a unique key pair and an associated certificate, identifying the DRM agent and certifying the binding between the agent and this key pair. This allows RIs to securely authenticate the DRM agent using standard PKI procedures. 
     The information in the certificate enables the RI to apply a policy based on its business rules, the value of its content, etc. For example, an RI may trust certain manufacturers, or it may keep an updated list of DRM agents that are known to be trusted or not trusted according to some criteria defined by the RI. 
     The DRM Content Format (DCF) is a secure content package for encrypted content, with its own MIME content type. In addition to the encrypted content, it contains additional information such as content description (original content type, vendor, version, etc.), RI uniform resource identifier (URI) (a location where an RO may be obtained), and so on. This additional information is not encrypted and may be presented to the user before an RO is retrieved. The CEK needed to unlock the DRM content inside a DCF is contained within the RO. Thus, it is not possible to access DRM content without the RO, and the DRM content can only be used as specified in the RO. The OMA DRM includes a mechanism allowing a DRM agent to verify the integrity of a DCF, protecting against modification of the content by an unauthorized entity. 
     The OMA DRM system assumes the presence of DRM time in the DRM agent. Since users are not able to change the DRM time, a mechanism is defined by which the DRM time can be synchronized with the time held by an OCSP responder. Some constraints (e.g., absolute time constraints), as well as some aspects of the delivery protocol for ROs, rely on the DRM agent having a secure time source. DRM time in the context of the OMA DRM specifications means an accurate time as well as a time value that is not changeable by users. The OMA DRM specifications provide mechanisms for the DRM time to be synchronized when necessary, e.g., if the DRM time is lost after a prolonged power failure. Some limited-capability unconnected devices may not support a real time clock and hence may not support DRM time. Connected devices, however, must support DRM time. 
     The OMA DRM protects against RO replay protection attacks. An example of an RO replay attack is where an intermediary intercepts an RO with a limited number of plays during delivery to the DRM agent. When the rights expire on the DRM agent, the intercepted RO might be delivered again (replayed) from the intermediary. The OMA DRM prevents this and similar attacks from occurring. 
     The OMA DRM system provides application-layer security through the use of the security mechanisms listed above. Hence, it does not rely on, or assume, transport layer security. 
     The ROAP plays a central part in the OMA DRM 2.0 in allowing secure, authentication-based exchange of information regarding ROs. The ROAP is the common name for a suite of DRM security protocols between an RI and a DRM agent in a device. The protocol suite contains several sub-protocols: 
     1. The 4-pass protocol for registering a device with an RI, as shown in  FIG. 2 . 
     2. The 2-pass RO acquisition protocol includes the request and delivery of an RO, as shown in  FIG. 3 . 
     3. The 1-pass RO acquisition protocol relates to the delivery of an RO from an RI to a device (e.g., messaging/push), as shown in  FIG. 4 . 
     4. The 2-pass join domain protocol for a device to join a domain, as shown in  FIG. 5 . 
     5. The 2-pass leave domain protocol for a device to leave a domain, as shown in  FIG. 6 . 
       FIG. 2  is a flow diagram the 4-pass registration protocol  200 . The protocol  200  utilizes a device  202 , an RI  204 , and an OCSP responder  206 . The device  202  initiates (possibly upon receipt of a ROAP trigger) the contact with the RI  204  by sending a Device Hello message (step  210 ), which contains information such as the device ID (a hash of a device&#39;s certificate that the RI  204  can later check with the OCSP responder  206 ) and other information. Table 1 illustrates the main components in the Device Hello message. None of the information in the Device Hello message is integrity protected, i.e., there is no signature for the message. 
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Format of the Device Hello message 
               
             
          
           
               
                   
                 Mandatory 
                   
               
               
                 Parameter 
                 or Optional 
                 Notes 
               
               
                   
               
               
                 Version 
                 Mandatory 
                 &lt;major.minor&gt; representation of the highest ROAP version 
               
               
                   
                   
                 number supported by ROAP. This value is 1.0 for OMA DRM 
               
               
                   
                   
                 v2.0. The device has to support all versions including and 
               
               
                   
                   
                 prior to the version specified. 
               
               
                 Device ID 
                 Mandatory 
                 Currently, the only ID defined is the SHA-1 hash of the 
               
               
                   
                   
                 device&#39;s public key information, as it appears in the 
               
               
                   
                   
                 certificate (i.e., the complete Distinguished Encoding Rules 
               
               
                   
                   
                 (DER)-encoded SubjectPublicKeyInfo component in the 
               
               
                   
                   
                 device certificate). If the device holds multiple keys, it may 
               
               
                   
                   
                 select one or more of these public keys and send the 
               
               
                   
                   
                 corresponding device IDs. 
               
               
                 Supported 
                 Optional 
                 Identifies the cryptographic algorithms (hash, MAC, 
               
               
                 Algorithms 
                   
                 signature, key transport, key wrap) identified by common 
               
               
                   
                   
                 URIs. All devices and RIs should support the algorithms 
               
               
                   
                   
                 specified in the OMA DRM 2.0. 
               
               
                 Extensions 
                 Optional 
                 Certificate Caching, to indicate to the RI that the device has 
               
               
                   
                   
                 the capability to store information in the RI context whether 
               
               
                   
                   
                 the RI has stored the device certificate information or not. 
               
               
                   
                   
                 The actual storage indicator is done by the Peer Key 
               
               
                   
                   
                 Identifier extension for the device&#39;s public key indication. 
               
               
                   
               
             
          
         
       
     
     The RI  204 , in response to the Device Hello message (step  210 ), sends an RI Hello message to the device  202  (step  212 ), which contains information such as the RI&#39;s certificate credentials (in the form of an RI ID), some session related (anti-reply-purpose) nonces and session numbers, and other optional information such as the information on the trust chain about the device that the RI  204  recognizes. Table 2 illustrates the format of the RI Hello message. It is noted that none of the information in the RI Hello message is integrity protected. 
     
       
         
               
             
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Format of the RI Hello message 
               
             
          
           
               
                   
                 ROAP-RI Hello 
                   
               
             
          
           
               
                   
                   
                 Status not 
                   
               
               
                 Parameter 
                 Status = “Success” 
                 “Success” 
                 Notes 
               
               
                   
               
               
                 Status 
                 Mandatory 
                 Mandatory 
                 Indicates whether the Device Hello 
               
               
                   
                   
                   
                 message handling was successful or 
               
               
                   
                   
                   
                 not. 
               
               
                 Session ID 
                 Mandatory 
                 — 
                 Protocol session ID set by the RI. 
               
               
                 Selected 
                 Mandatory 
                 — 
                 Minimum of (device suggested 
               
               
                 Version 
                   
                   
                 ROAP version, highest RI 
               
               
                   
                   
                   
                 supported ROAP version). 
               
               
                 RI ID 
                 Mandatory 
                 — 
                 The only currently defined ID is the 
               
               
                   
                   
                   
                 hash of the RI&#39;s public key 
               
               
                   
                   
                   
                 information, as appearing in the 
               
               
                   
                   
                   
                 RI&#39;s certificate. If the RI holds 
               
               
                   
                   
                   
                 multiple keys, the RI must select 
               
               
                   
                   
                   
                 only one key. 
               
               
                 Selected 
                 Optional 
                 — 
                 Cryptographic algorithms to use in 
               
               
                 Algorithm 
                   
                   
                 subsequent ROAP interactions. 
               
               
                 RI Nonce 
                 Mandatory 
                 — 
                 A random nonce sent by the RI. 
               
               
                 Trusted device 
                 Optional 
                 — 
                 List of device trust anchors 
               
               
                 Authorities 
                   
                   
                 recognized by the RI. It is not sent 
               
               
                   
                   
                   
                 if the RI already has a device 
               
               
                   
                   
                   
                 certificate or otherwise can trust 
               
               
                   
                   
                   
                 the device. 
               
               
                 Server Info 
                 Optional 
                 — 
                 &lt;=512 byte server-specific 
               
               
                   
                   
                   
                 information that the device later 
               
               
                   
                   
                   
                 must return unchanged in the 
               
               
                   
                   
                   
                 Registration Request message. The 
               
               
                   
                   
                   
                 device must not try to interpret this 
               
               
                   
                   
                   
                 information. 
               
               
                 Extensions 
                 Optional 
                 — 
                 Peer Key Identifier, Certificate 
               
               
                   
                   
                   
                 Caching, Device Details: by 
               
               
                   
                   
                   
                 including this, the RI requests the 
               
               
                   
                   
                   
                 device to return device-specific 
               
               
                   
                   
                   
                 information (manufacturer, model, 
               
               
                   
                   
                   
                 etc.) in a subsequent Registration 
               
               
                   
                   
                   
                 Request message. 
               
               
                   
               
             
          
         
       
     
     Upon successful verification of the information contained in the RI Hello message, the device  202  sends a Registration Request message (step  214 ) that includes mandatory information such as the request time, session ID, and a signature and optional information such as a certificate chain, trusted RI authority anchor, extensions, etc. Table 3 illustrates the format of the Registration Request message. The Registration Request message contains, at its tail end, a digital signature of all the messages exchanged between the device  202  and the RI  204  up to the Signature field in the Registration Request message, i.e., the entire Device Hello message, the entire RI Hello message, and the fields of the Registration Request message up to (and excluding) the Signature field. This digital signature is made using the device&#39;s private key. Including the digital signature provides some integrity protection of the associated ROAP messages. 
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 Format of the Registration Request message 
               
             
          
           
               
                   
                 Registration 
                   
               
               
                 Parameter 
                 Request 
                 Notes 
               
               
                   
               
               
                 Session ID 
                 Mandatory 
                 Same as the session ID in the RI Hello message. If not 
               
               
                   
                   
                 the same, then the RI terminates the registration protocol. 
               
               
                 Device Nonce 
                 Mandatory 
                 A nonce chosen by the device. 
               
               
                 Request Time 
                 Mandatory 
                 The current DRM time as measured by the device. 
               
               
                 Certificate 
                 Optional 
                 A certificate chain includes the device&#39;s certificate but 
               
               
                 Chain 
                   
                 not the root certificate. The certificate chain is present 
               
               
                   
                   
                 unless the RI Hello message contained the Peer Key 
               
               
                   
                   
                 Identifier extension and its value identified the key in 
               
               
                   
                   
                 the device&#39;s current certificate. If the RI indicated trust 
               
               
                   
                   
                 anchor preferences in the RI Hello message, the device 
               
               
                   
                   
                 must select a device certificate and chain which chains 
               
               
                   
                   
                 back to one of the trust anchors indicated by the RI. 
               
               
                 Trusted RI 
                 Optional 
                 List of RI trust anchors recognized by the device. If 
               
               
                 Authorities 
                   
                 empty, it indicates that the RI is free to choose any 
               
               
                   
                   
                 certificate. 
               
               
                 Server Info 
                 Optional 
                 Only (must be) present if a Server Info parameter was 
               
               
                   
                   
                 present in the RI Hello message. If present, this field 
               
               
                   
                   
                 must be the same as in the RI Hello message. 
               
               
                 Extensions 
                 Optional 
                 Peer Key Identifier; No OCSP Response; OCSP 
               
               
                   
                   
                 Responder Key Identifier; Device Details 
               
               
                   
                   
                 (manufacturer, model, version). 
               
               
                 Signature 
                 Mandatory 
                 An SHA-1 hash of data sent so far in the protocol, 
               
               
                   
                   
                 excluding this Signature element. Made using the 
               
               
                   
                   
                 device&#39;s private key. 
               
               
                   
               
             
          
         
       
     
     Unless the device  202  indicates, via information in the Extensions, that OCSP verification is not necessary or supported, the RI  204  sends an OCSP Request message to the OCSP Responder  206  (step  216 ) to request verification of the information supplied to the RI  204  by the device  202 . The OCSP Responder  206  looks up the information in the request message to attempt to verify the information and returns an OCSP Response message (step  218 ) containing the results of the request. 
     The RI  204  sends a Registration Response message to the device  202  (step  220 ), which include an indication of whether the registration was successful or unsuccessful and other information. Table 4 illustrates the format of the Registration Response message. The Registration Response message contains, at its tail end, an SHA-1 hash of the Registration Request message and the Registration Response message (up to and excluding the Signature field). This digital signature is made using the RI&#39;s private key. Including the digital signature provides some integrity protection of the associated ROAP messages. It is noted that while the SHA-1 hash is used for the digital signature, any suitable algorithm for applying the digital signature could be used. 
     
       
         
               
             
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 4 
               
             
             
               
                   
               
               
                 Format of the Registration Response message 
               
             
          
           
               
                   
                 Registration Response 
                   
               
             
          
           
               
                   
                   
                 Status not 
                   
               
               
                 Parameter 
                 Status = “Success” 
                 “Success” 
                 Notes 
               
               
                   
               
               
                 Status 
                 Mandatory 
                 Mandatory 
                 Indicates whether the Device Hello message 
               
               
                   
                   
                   
                 handling was successful or not. 
               
               
                 Session ID 
                 Mandatory 
                 — 
                 The protocol session ID set by the RI. 
               
               
                 Selected 
                 Mandatory 
                 — 
                 The minimum of (device suggested ROAP 
               
               
                 Version 
                   
                   
                 version, highest RI supported ROAP version). 
               
               
                 RI ID 
                 Mandatory 
                 — 
                 The only currently defined ID is the hash of the 
               
               
                   
                   
                   
                 RI&#39;s public key information, as appearing in the 
               
               
                   
                   
                   
                 RI&#39;s certificate. If the RI holds multiple keys, the 
               
               
                   
                   
                   
                 RI must select only one key. 
               
               
                 Selected 
                 Mandatory 
                 — 
                 Cryptographic algorithms to use in subsequent 
               
               
                 Algorithm 
                   
                   
                 ROAP interactions. 
               
               
                 RI Nonce 
                 Mandatory 
                 — 
                 A random nonce sent by the RI. 
               
               
                 Trusted 
                 Optional 
                 — 
                 List of device trust anchors recognized by the 
               
               
                 device 
                   
                   
                 RI. It is not sent if the RI already has a device 
               
               
                 Authorities 
                   
                   
                 certificate or otherwise can trust the device. 
               
               
                 Server Info 
                 Optional 
                 — 
                 &lt;=512 byte server-specific information that the 
               
               
                   
                   
                   
                 device later must return unchanged in the 
               
               
                   
                   
                   
                 Registration Request message. The device must 
               
               
                   
                   
                   
                 not try to interpret this information. 
               
               
                 Extensions 
                 Optional 
                 — 
                 Peer Key Identifier, Certificate Caching, Device 
               
               
                   
                   
                   
                 Details: by including this, the RI requests the 
               
               
                   
                   
                   
                 device to return device-specific information 
               
               
                   
                   
                   
                 (manufacturer, model) in the subsequent 
               
               
                   
                   
                   
                 Registration Request message. 
               
               
                 Signature 
                 Mandatory 
                 — 
                 SHA-1 has of the Registration Request message 
               
               
                   
                   
                   
                 and the Registration Response message 
               
               
                   
                   
                   
                 (excluding the Signature field), using the RI&#39;s 
               
               
                   
                   
                   
                 private key. 
               
               
                   
               
             
          
         
       
     
       FIG. 3  is a flow diagram of the 2-pass RO Acquisition Protocol  300 . The protocol  300  utilizes the device  202  and the RI  204 , and operates after the 4-pass Registration Protocol  200  has been completed and the device  202  has received a valid certificate chain about the RI  204 . The protocol  300  is used by the device  202  to request an RO from the RI  204 . The device  202  sends an RO Request message to the RI  204  to request the RO (step  310 ). Table 5 shows the format of the RO Request message. The RO Request message contains a digital signature of the message (excluding the signature field). 
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 5 
               
             
             
               
                   
               
               
                 Format of the RO Request message 
               
             
          
           
               
                   
                 ROAP-RO 
                   
               
               
                   
                 Request 
               
               
                   
                 Mandatory/ 
               
               
                 Parameter 
                 Optional 
                 Notes 
               
               
                   
               
               
                 Device ID 
                 M 
                 Identifies the requesting device. 
               
               
                 Domain ID 
                 O 
                 When present, identifies the domain. 
               
               
                 RI ID 
                 M 
                 Authorizing RI ID. Same value as in the Registration 
               
               
                   
                   
                 Response message. 
               
               
                 Device Nonce 
                 M 
                 A nonce chosen by device. 
               
               
                 Request Time 
                 M 
                 The current DRM Time, as seen by the device. 
               
               
                 RO Info 
                 M 
                 IDs of the requested RO(s), and also an optional hash of 
               
               
                   
                   
                 the DCF if the device possesses the DCF. 
               
               
                 Certificate 
                 O 
                 Sent unless the RI context indicates that the device has 
               
               
                 Chain 
                   
                 the necessary certificate information. Must include the 
               
               
                   
                   
                 device&#39;s certificate. 
               
               
                 Extensions 
                 O 
                 Peer Key Identifier; No OCSP Response; OCSP 
               
               
                   
                   
                 Responder Key Identifier; Transaction ID 
               
               
                 Signature 
                 M 
                 An SHA-1 hash of the RO Request message without the 
               
               
                   
                   
                 Signature element. 
               
               
                   
               
             
          
         
       
     
     The RI  204 , in response to the request message, sends an RO Response message to the device  202  (step  312 ). The RO response message includes an RO or includes an indication that an RO will not be sent. 
     Table 6 shows the format of the RO response message. The RO Response message, in successful state case, contains a digital signature that is an SHA-1 hash of the RO Request message and the RO Response message excluding the Signature field. 
     
       
         
               
             
               
               
               
               
             
           
               
                 TABLE 6 
               
             
             
               
                   
               
               
                 Format of the RO Response message 
               
             
          
           
               
                   
                   
                 2-Pass 
                   
               
               
                   
                 2-Pass 
                 not 
               
               
                 Parameter 
                 Success 
                 Success 
                 Notes 
               
               
                   
               
               
                 Status 
                 M 
                 M 
                 Indicates if the request was handled 
               
               
                   
                   
                   
                 successfully or not. 
               
               
                 Device ID 
                 M 
                 — 
                 Identifies the requesting device, in the 
               
               
                   
                   
                   
                 same way as in the Device Hello message. 
               
               
                   
                   
                   
                 This value must be the same as in RO 
               
               
                   
                   
                   
                 Request message. Must terminate if not. 
               
               
                 RI ID 
                 M 
                 — 
                 Identifies the RI and must equal the RI 
               
               
                   
                   
                   
                 ID in the RO Request message. 
               
               
                 Device 
                 M 
                 — 
                 Must have the same value as in the RO 
               
               
                 Nonce 
                   
                   
                 Request message. 
               
               
                 Protected 
                 M 
                 — 
                 ROs in which sensitive information (such 
               
               
                 ROs 
                   
                   
                 as CEKs) are encrypted. 
               
               
                 Certificate 
                 O 
                 — 
                 Same as in the Registration Response 
               
               
                 Chain 
                   
                   
                 message. 
               
               
                 OCSP 
                 O 
                 — 
                 Complete set of OCSP responses for the 
               
               
                 Response 
                   
                   
                 RI&#39;s certificate chain. 
               
               
                 Extensions 
                 O 
                 — 
                 Transaction Identifier that allows the RI 
               
               
                   
                   
                   
                 to provide the device with information for 
               
               
                   
                   
                   
                 tracking transactions. 
               
               
                 Signature 
                 M 
                 — 
                 An SHA-1 hash of the RO Request 
               
               
                   
                   
                   
                 message and the RO Response message 
               
               
                   
                   
                   
                 (without this Signature field) using the 
               
               
                   
                   
                   
                 RI&#39;s private key. 
               
               
                   
               
             
          
         
       
     
       FIG. 4  is a flow diagram of the 1-pass RO Acquisition Protocol  400 . The protocol  400  utilizes the device  202  and the RI  204 . In the protocol  400 , the RI  204  unilaterally sends, without request by the device  202 , an RO response message to the device  202  (step  410 ) including the RO. The protocol  400  applies to the push use cases, for example. Table 7 shows the format of the RO Response message. 
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 7 
               
             
             
               
                   
               
               
                 Format of the RO Response message 
               
             
          
           
               
                 Parameter 
                 1-Pass 
                 Notes 
               
               
                   
               
               
                 Status 
                 M 
                 Indicates if the request was handled successfully or not. 
               
               
                 Device ID 
                 M 
                 Identifies the requesting device, in the same way as in 
               
               
                   
                   
                 the Device Hello message. This value must be the same 
               
               
                   
                   
                 as in the RO Request message. Must terminate if not. 
               
               
                 RI ID 
                 M 
                 Identifies the RI and must equal the stored RI ID. 
               
               
                 Device Nonce 
                 — 
                 Must have same value as in the RO Request message. 
               
               
                 Protected ROs 
                 M 
                 ROs in which sensitive information (such as CEKs) are 
               
               
                   
                   
                 encrypted. 
               
               
                 Certificate 
                 O 
                 Same as in the Registration Response message. 
               
               
                 Chain 
               
               
                 OCSP Response 
                 M 
                 Complete set of OCSP responses for the RI&#39;s certificate 
               
               
                   
                   
                 chain. 
               
               
                 Extensions 
                 O 
                 Transaction Identifier that allows RI to provide the 
               
               
                   
                   
                 device with information for tracking transactions. 
               
               
                 Signature 
                 M 
                 An SHA-1 hash of the RO Response message without 
               
               
                   
                   
                 this Signature field. The RI&#39;s private key is used to generate 
               
               
                   
                   
                 this Signature. 
               
               
                   
               
             
          
         
       
     
       FIG. 5  is a flow diagram of the 2-pass Join Domain Protocol  500 . The protocol  500  utilizes the device  202  and the RI  204 . When the device  202  wants to join a domain, the device  202  sends a Join Domain Request message to the RI  204  (step  510 ). The RI  204  evaluates the request and sends a Join Domain Response message to the device  202  (step  512 ). Table 8 shows the format of the Join Domain Request message and Table 9 shows the format of the Join Domain Response message. 
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 8 
               
             
             
               
                   
               
               
                 Format of the Join Domain Request Message 
               
             
          
           
               
                   
                 Mandatory 
                   
               
               
                 Parameter 
                 or Optional 
                 Notes 
               
               
                   
               
               
                 Device ID 
                 M 
                 Identifies the requesting device. This value 
               
               
                   
                   
                 must be the same as the stored value from the 
               
               
                   
                   
                 Registration Response message. 
               
               
                 RI ID 
                 M 
                 Identifies the RI and must equal the stored RI 
               
               
                   
                   
                 ID from the Registration Response message. 
               
               
                 Device 
                 M 
                 Nonce chosen by the device. 
               
               
                 Nonce 
               
               
                 Request 
                 M 
                 Current DRM Time, as seen by the device. 
               
               
                 Time 
                   
                 Unconnected Devices that do not support DRM 
               
               
                   
                   
                 Time MUST use the value “Undefined” here. 
               
               
                 Domain 
                 M 
                 Identifies the Domain the device wishes to join. 
               
               
                 Identifier 
               
               
                 Certificate 
                 O 
                 This parameter is sent unless Certificate 
               
               
                 Chain 
                   
                 Caching is indicated in the RI Context with 
               
               
                   
                   
                 this RI. When present, the parameter value 
               
               
                   
                   
                 shall be as described for the Certificate Chain 
               
               
                   
                   
                 parameter in the Registration Response 
               
               
                   
                   
                 message. 
               
               
                 Extensions 
                 O 
                 Includes extensions Peer Key Identifier, No 
               
               
                   
                   
                 OCSP Response, OCSP Responder Key 
               
               
                   
                   
                 Identifier, and Hash Chain Support. 
               
               
                 Signature 
                 M 
                 An SHA-1 hash of the Join Domain Request 
               
               
                   
                   
                 message (without this Signature field) using 
               
               
                   
                   
                 the device&#39;s private key. 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
               
             
           
               
                 TABLE 9 
               
             
             
               
                   
               
               
                 Format of the Join Domain Response Message 
               
             
          
           
               
                   
                   
                 Status is 
                   
               
               
                   
                   
                 NOT 
               
               
                 Parameter 
                 Status = Success 
                 Success 
                 Notes 
               
               
                   
               
               
                 Status 
                 M 
                 M 
                 Indicates if the request was handled 
               
               
                   
                   
                   
                 successfully or not. 
               
               
                 Device ID 
                 M 
                 — 
                 Identifies the requesting device. The 
               
               
                   
                   
                   
                 value returned here must be the same as 
               
               
                   
                   
                   
                 in Join Domain Request message that 
               
               
                   
                   
                   
                 triggered this response. 
               
               
                 RI ID 
                 M 
                 — 
                 The value returned here must equal the 
               
               
                   
                   
                   
                 RI ID sent by the device in the preceding 
               
               
                   
                   
                   
                 Join Domain Request message. 
               
               
                 Device Nonce 
                 M 
                 — 
                 Must have the same value as in the 
               
               
                   
                   
                   
                 preceding Join Domain Request message. 
               
               
                 Domain Info 
                 M 
                 — 
                 This parameter carries Domain keys 
               
               
                   
                   
                   
                 (encrypted using Device&#39;s public key) as 
               
               
                   
                   
                   
                 well as information about the maximum 
               
               
                   
                   
                   
                 lifetime of the Domain. Devices may use a 
               
               
                   
                   
                   
                 shorter lifetime than suggested by the RI. 
               
               
                 Certificate 
                 O 
                 — 
                 This parameter MUST be present unless 
               
               
                 Chain 
                   
                   
                 a preceding ROAP Join Domain Request 
               
               
                   
                   
                   
                 message contained the Peer Key Identifier 
               
               
                   
                   
                   
                 extension, the extension was not ignored 
               
               
                   
                   
                   
                 by the RI, and its value identified the RI&#39;s 
               
               
                   
                   
                   
                 current key. When present, the value of a 
               
               
                   
                   
                   
                 Certificate Chain parameter shall be as 
               
               
                   
                   
                   
                 described for the Certificate Chain 
               
               
                   
                   
                   
                 parameter of the Registration Response 
               
               
                   
                   
                   
                 message. 
               
               
                 OCSP 
                 O 
                 — 
                 A complete set of valid OCSP responses 
               
               
                 Response 
                   
                   
                 for the RI&#39;s certificate chain. 
               
               
                 Extensions 
                 O 
                 — 
                 Currently only one extension is defined 
               
               
                   
                   
                   
                 for the Join Domain Response message. It 
               
               
                   
                   
                   
                 is Hash Chain Support. When this 
               
               
                   
                   
                   
                 extension is present it indicates that the 
               
               
                   
                   
                   
                 RI is using the technique of generation 
               
               
                   
                   
                   
                 Domain Keys through hash chains 
               
               
                   
                   
                   
                 described in the Domain Section. The RI 
               
               
                   
                   
                   
                 MUST NOT include this extension in the 
               
               
                   
                   
                   
                 Join Domain Response unless the same 
               
               
                   
                   
                   
                 extension was received in the preceding 
               
               
                   
                   
                   
                 Join Domain Request. 
               
               
                 Signature 
                 M 
                 — 
                 An SHA-1 hash of the Join Domain 
               
               
                   
                   
                   
                 Response message excluding the 
               
               
                   
                   
                   
                 signature field itself. 
               
               
                   
               
             
          
         
       
     
       FIG. 6  is a flow diagram of the 2-pass Leave Domain Protocol  600 . The protocol  600  utilizes the device  202  and the RI  204 . When the device  202  wants to leave a domain, the device  202  sends a Leave Domain Request message to the RI  204  (step  610 ). The RI  204  evaluates the request and sends a Leave Domain Response message to the device  202  (step  612 ). Table 10 shows the format of the Leave Domain Request message and Table 11 shows the format of the Leave Domain Response message. 
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 10 
               
             
             
               
                   
               
               
                 Format of the Leave Domain Request Message 
               
             
          
           
               
                   
                 Mandatory 
                   
               
               
                 Parameter 
                 or Optional 
                 Notes 
               
               
                   
               
               
                 Device ID 
                 M 
                 Identifies the requesting device. This value 
               
               
                   
                   
                 must be the stored value from the Registration 
               
               
                   
                   
                 Response message. 
               
               
                 RI ID 
                 M 
                 Identifies the RI and must equal stored RI ID 
               
               
                   
                   
                 from the Registration Response message. 
               
               
                 Device 
                 M 
                 Nonce chosen by the device. 
               
               
                 Nonce 
               
               
                 Request 
                 M 
                 Current DRM Time, as seen by the device. 
               
               
                 Time 
                   
                 Unconnected Devices that do not support DRM 
               
               
                   
                   
                 Time MUST use the value “Undefined” here. 
               
               
                 Domain 
                 M 
                 Identifies the Domain the device wishes to 
               
               
                 Identifier 
                   
                 leave. 
               
               
                 Certificate 
                 O 
                 This parameter is sent unless Certificate 
               
               
                 Chain 
                   
                 Caching is indicated in the RI Context with 
               
               
                   
                   
                 this RI. When present, the parameter value 
               
               
                   
                   
                 shall be as described for the Certificate Chain 
               
               
                   
                   
                 parameter in the Registration Response 
               
               
                   
                   
                 message. 
               
               
                 Extensions 
                 O 
                 The Not a Domain Member extension is 
               
               
                   
                   
                 currently defined for Leave Domain Request 
               
               
                   
                   
                 message. Presence of this extension indicates 
               
               
                   
                   
                 to the RI that the device does not consider 
               
               
                   
                   
                 itself a member of this Domain (even though it 
               
               
                   
                   
                 is sending a request for the RI to remove it 
               
               
                   
                   
                 from the Domain). This could happen, for 
               
               
                   
                   
                 example, if the device already has left the 
               
               
                   
                   
                 Domain, but receives a new trigger to leave it 
               
               
                   
                   
                 (perhaps because the RI never received the 
               
               
                   
                   
                 previous ROAP Leave Domain Request 
               
               
                   
                   
                 message). This extension MUST be included in 
               
               
                   
                   
                 the request if the device is not a member of the 
               
               
                   
                   
                 identified Domain. 
               
               
                 Signature 
                 M 
                 An SHA-1 hash of the Leave Domain Request 
               
               
                   
                   
                 message (without this Signature field) using 
               
               
                   
                   
                 the device&#39;s private key. 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
               
             
           
               
                 TABLE 11 
               
             
             
               
                   
               
               
                 Format of the Leave Domain Response Message 
               
             
          
           
               
                   
                   
                 Status is 
                   
               
               
                   
                   
                 NOT 
               
               
                 Parameter 
                 Status = Success 
                 Success 
                 Notes 
               
               
                   
               
               
                 Status 
                 M 
                 M 
                 Indicates if the request was handled 
               
               
                   
                   
                   
                 successfully or not. 
               
               
                 Device Nonce 
                 M 
                 — 
                 Must have the same value as in the 
               
               
                   
                   
                   
                 preceding Leave Domain Request 
               
               
                   
                   
                   
                 message. 
               
               
                 Domain 
                 M 
                 — 
                 The domain from which the RI removed 
               
               
                 Identifier 
                   
                   
                 the device. 
               
               
                 Extensions 
                 O 
                 — 
                 No extensions are currently defined for 
               
               
                   
                   
                   
                 Leave Domain Response message. 
               
               
                   
               
             
          
         
       
     
     All of the protocols included in the ROAP suite except the 1-pass RO Acquisition Protocol may be initiated using a ROAP trigger. The device  202  may also initiate the protocols unilaterally as a result of user interactions. The RI  204  generates and sends the ROAP trigger to the device  202  to trigger a ROAP protocol exchange. Alternatively, the RI  204  may delegate ROAP trigger generation to other systems by providing the necessary information (such as RO identifiers and domain identifiers) to these systems. A ROAP trigger (whether generated directly or indirectly by the RI  204 ) may also be transmitted to the device  202  by other systems (e.g., by a CI). 
     When the device  202  receives the ROAP trigger, it initiates the ROAP protocol exchange as soon as possible. Appropriate user consent must have been obtained prior to initiating any ROAP protocols as a result of receiving a ROAP trigger. Since the ROAP comprises several protocols, the ROAP trigger includes an indication of the actual protocol (e.g., Registration, RO Acquisition, Join Domain, or Leave Domain) to be started by the device  202 . 
     The ROAP messages and how the messages are handled by the protocols provide not only the ROs and their associated processing, but also security functions surrounding the ROs in the OMA DRM 2.0. More specifically, the following security and trust aspects are addressed by the ROAP protocols: 
     1. Mutual authentication between the RI and the device; 
     2. Countering replay attacks by using nonces in various messages; 
     3. Protecting the integrity of the ROAP messages or parts of the ROAP messages; and 
     4. Verification of secure DRM Time in the ROAP messages or parts of the ROAP messages. 
     Trusted Computing Techniques 
     Recently, trusted computing techniques have appeared in the literature and in products, mostly under the technical umbrella of the Trusted Computing Group (TCG). The TCG technologies provide methods whereby computing entities can establish trustworthiness for themselves and for other devices by way of using of a trust chain, so that processing or computing on such devices can be: 
     1. Assessed for the trustworthiness of the platform and various hardware (HW) and software (SW) components; 
     2. Validated only when the appropriate trust level is established and can be validated for itself and for others upon external requests; and 
     3. External parties can perform assessments and decisions on the exchange of information and processing with other devices and is based on the manifested trust levels of such target devices. 
     The TCG defines a core processing module called the Trusted Processing Module (TPM) that has the following features: 
     1. Physical protection of the module and its interfaces; 
     2. Protected volatile and non-volatile storage spaces; 
     3. Protected cryptographic functions inside the module that can perform encryption and digital signing; 
     4. Use of Platform Configuration Registers (PCR) that consecutively capture the “state” of the platform and its SW components by hash extending; 
     5. Existence of device specific and secure Endorsement Keys (EK), based on a PKI that serves as the root of the authentication of the device but not in direct ways. The EK is never exposed outside, but its aliases, called the Attestation Identity Keys (AIKs), are used to sign the platform&#39;s integrity measurement values; and 
     6. Use of “sealing” of data, in conjunction with PCR values signed by AIKs, in memory “blobs”, so that data can be accessed or extracted only when platform or SW integrity (as measured and verified by the matching PCR values from the TPM and from the sealed memory blob) is verified. 
     Trusted computing techniques were inspected, especially in the context of mobile phone devices, for possible application in securing the DRM application on such mobile devices. Methods previously proposed to secure the DRM application by use of TCG techniques included certain methods that use the procedure of TPM sealing and the memory blobs to securely store the DRM-related data after ROAP protocol processing using TCG keys, in the TPM and in storage areas with key protection. 
     However, the existing prior art does not explicitly address nor address in an orderly way how to establish and use “trust” on the platform and/or the DRM software. Nor does the prior art address specific techniques to secure the integrity in the ROAP messages, to strengthen the integrity processing in OMA DRM 2.0 systems. The present invention includes new techniques for such purposes. 
     The current OMA DRM 2.0 specification provides strong security methods based on PKI involving the CA, the RIs, and the device. However, there are vulnerabilities related to the security and integrity of the platforms, SW, agents, and messages both within the OMA DRM 2.0 specification itself and as related to the non-specified implementation of the devices and RIs that are OMA DRM 2.0 compliant. 
     The OMA DRM specification has acknowledged the various threats and vulnerabilities that any device or RI could face, even when they are conforming to the OMA DRM 2.0 specification. These vulnerabilities include: 
     1. Entity Compromise, where an attacker may attempt to compromise an entity of the DRM system, physically or otherwise. Types of entity compromise attacks include compromising the DRM agent on the device and the DRM SW in the RI. The consequences of entity compromises include disclosure of private keys, domain keys, RO encryption keys, content encryption keys, and protected content, as well as the loss of integrity protection of the DRM agent&#39;s replay cache, for example, and/or the loss of protection of the rights stored internally in the DRM agent. Further, losses of DRM time could also occur. The effects on a PKI of a compromised CA or OCSP Responder is discussed in references such as IETF RFC3280. 
     The OMA DRM system relies on certificate revocation to minimize the damage caused by a compromised entity. DRM agents and RIs must always verify that the entity they are communicating with has not been compromised, by checking the entity&#39;s certificate status. An entity compromise attack can take place in both “forward” and “reversed” ways. A forward compromise attack is on the DRM entities (the RI, the DRM agent, the CI, the CA, or the OCSP responder), leading to unauthorized behavior. A reversed compromise attack neutralizes or weakens a DRM agent&#39;s security, integrity settings, and configurations. 
     2. Message Removal, whereby an attacker may remove a message sent between a DRM agent and an RI, typically resulting in Denial of Service (DoS) attacks. A message removal attack can include: message removal during the registration protocol or the RO acquisition protocol, replay nonce removal, removal of ROAP trigger, etc. 
     3. Message Modification, whereby an attacker may modify any message sent between a DRM agent and an RI, typically resulting in DoS attacks. A message modification attack can include modification during the registration protocol, during the join domain and leave domain protocols, and to various ROAP triggers. 
     4. Message Insertion, whereby an attacker may insert messages into the communication channel at any point between an RI and a DRM agent. The attacker may also record messages and try to replay them at a later point in time. A message insertion attack can include messages inserted while in the registration protocol, the 2-pass and 1-pass RO acquisition protocols, and to various ROAP triggers. 
     5. Other attacks such as general DoS attacks, passive attacks such as traffic analysis, and privacy disclosing. 
     The following problems of the current OMA DRM specifications and implementations are identified. An expanded notion of “integrity” as applied to the OMA DRM schemes is defined. In the traditional sense, the OMA DRM specifications only address a small scope of ROAP message integrity. In the expanded notion of integrity defined in the present invention, it is noted where and what kind of integrity can be considered in the following. 
     1. DRM Platform Integrity. This relates to integrity at or within the platform entities, i.e., at the physical entities comprising the device, the RI, and the content functions. The different entities include the operating system (OS), the boot code (e.g., the BIOS in the PC case), the HW/firmware (FW)/SW for memory access, the various HW/FW/SW entities that process security related functions (such as cryptography and key management, as well as privileged storage of secret data such as policies, certificates, etc.), and the network and local connectivity HW/FW/SW. Platform integrity determines whether the platform is valid, genuine, not modified except by legitimate processes, and operates only as intended. 
     2. DRM SW Integrity. DRM SW refers to software entities and components residing in the device, the RI, or the CI that perform functions specific to OMA DRM specifications and their procedures. At the device, the DRM agent consists of the DRM SW. At the RI and the CI, the DRM SW refers collectively to the set of SW that performs the DRM-specific functions such as RO packaging, DCF formatting, content encryption, content or RO delivery, verification, ROAP processing, etc. DRM SW integrity is maintained if the DRM SW is valid, genuine, not modified except by legitimate processes, and operates only as intended. 
     3. Integrity of the ROAP messages and information. The integrity of the ROAP messages and their constituent information is maintained if such information is validated, genuine, and not modified except by legitimate processes. In the OMA DRM 2.0 specifications, certain subsets of ROAP messages and their constituent information are integrity protected by use of digital signatures. 
     4. Integrity of the media object and DRM content. The media objects and the DRM content must also be integrity protected, i.e., must not be modified, removed, or falsely inserted, whether they are stored at the device, the RI, or the CI, or are in transit or delivery between any two parties. Of particular interest is the over-the-air (OTA) delivery of content, as applicable to the transfer of content to a mobile device, where the DRM content is delivered using essentially open channels. 
     5. Integrity of DRM-related information. DRM-related information such as the entity IDs (device ID, RI ID, etc.), encryption keys (CEK, REK) and signature keys, the ROs themselves, context information, certificates, and other trust-chain related information must be securely protected, which means that they should be protected not only for confidentiality but also for integrity. 
     It is noted that neither the current OMA DRM 2.0 specifications nor existing prior art appear to have proposed solutions to the entity compromise or integrity problems. This lack of solutions poses the following problem: Even if all the ROAP procedures are correctly implemented as according to the OMA DRM 2.0 specification, for example, how can a device really know whether the RI&#39;s platform is trustworthy? In other words, how can the device know whether the RI&#39;s platform will not abuse the data that the device sends as part of the ROAP protocols or abuse the DRM processing itself? For example, the device does not know whether the RI will arbitrarily and incorrectly limit the usage rights of the device because the RI&#39;s platform SW is compromised and it limits the otherwise valid usage rights of the device. Similar questions arise for the problem of the integrity of the DRM software. More specifically, some of the problems of the current OMA DRM 2.0 systems as viewed from the expanded notion of integrity as described above, are as follows. 
     1. A lack of methods to check and report the integrity of the platform and the DRM SW. As related to the entity compromise threat identified above, there is no method in the prior art for explicit and structured platform integrity verification and SW agent integrity verification between the device and the RI, either as specified by the OMA DRM 2.0 specifications or as part of the TCG 1.2 Use Cases. This is particularly true for platform integrity verification, rather than just the DRM agent. 
     2. A platform (such as a PC or PDA, as related to the device, or a server, as for the RI) could be maliciously compromised, which may result in preventing the DRM agent and the RI agent SW from performing correctly, even given correct and confidentiality-protected and integrity-protected information. For example, an otherwise well-protected DRM agent SW may store some information in plaintext in a shared memory prior to, during, or after processing. A compromised platform may, in such cases, egregiously access the shared memory and remove the information, alter the information, or insert new false information, which then could be processed subsequently by the DRM agent SW which may perceive such false information as genuine. This may result in DoS attacks, unauthorized disclosure of private information, or unauthorized delivery, distribution, or consumption of DRM ROs or DRM content. 
     3. The DRM agent SW and the RI SW, which are pieces of SW that process DRM-related information, may become compromised for various reasons. Such SW, for example, could be altered by a virus or other malicious SW entities. One result of such a compromise in the platform or the DRM SW would be a subsequent compromise in the integrity of the messages and information that the OMA DRM 2.0 considers, especially the ROAP protocol messages. Partly because only some, but not all, of the ROAP messages are integrity-protected, they can in theory be manipulated in synchronized ways between a compromised device and a rogue or compromised RI. Messages could be modified synchronously at both the device and the RI, and still may appear to be “integrity verified”, since the messages were modified in the same way. 
     4. Insufficient integrity protection of the ROAP messages. As related to the message integrity, the ROAP messages and the information carried by the various message fields are subject to vulnerabilities that are not solved by the OMA DRM 2.0 specification. For example, the ROAP message integrity protection currently specified in the OMA DRM 2.0 specification leaves holes such as: 
     4A. Not all ROAP messages are integrity protected. Not including digital signatures in all the messages could pose vulnerabilities in certain cases. 
     4B. Even when ROAP messages or certain fields of information are integrity protected by digital signatures, once such information has been decrypted, integrity checked, and then “used” in plaintext, malicious entities could access the plaintext information and remove, alter, or redistribute the previously integrity-checked information. Thus, a strengthened integrity protection is required. 
     5. Vulnerabilities regarding the integrity of the DRM content and its delivery. More specifically, the following problems exist: 
     5A. Content integrity checking mechanisms are incomplete. For example, integrity of the content while the content is in transit or in delivery (e.g., OTA download) is not specified. The signature for the DCF, for example, is only generated for use in the ROAP procedures. Until and before the ROAP procedures take place, there is no integrity checking mechanism that manages the content integrity while in storage at the CI, for example. 
     5B. Content encryption, even for use in the ROAP protocol, is mandatory but integrity checking is only optional. 
     5C. Especially for packetized content for streaming services, the PDCF format has a timing issue. Packets that had been illegitimately modified could be downloaded and may even be consumed (i.e., played on a media player) before the integrity of the whole stream can be checked. 
     The central problem becomes: how can the various parties (the device, the RI, and the CI) be assured of the platform integrity and the DRM SW integrity? Thus, a method to strengthen and verify the integrity of the platform (e.g., the OS, the BIOS, drivers, media player, communication software, shared memory, etc.) upon which either the DRM agent SW or the RI SW rely, is needed. The present invention addresses the shortcomings of the prior art. 
     SUMMARY 
     The present invention discloses several methods that strengthen the integrity of entities, messages, and processing related to the OMA DRM specification v2.0. The methods use techniques commonly known as Trusted Computing techniques, as specified by the industry forum Trusted Computing Group (TCG). In a first embodiment of the invention, techniques to verify platform and DRM SW integrity or trustworthiness, both with and without modifications to the DRM ROAP and DCF specifications, are disclosed. In a second embodiment, techniques to strengthen the integrity of the OMA DRM ROAP messages, constituent information, and processing without changing the existing ROAP protocol are disclosed. In a third embodiment, techniques to strengthen the integrity of ROAP messages, information and processing with some changes in the existing ROAP protocol are disclosed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more detailed understanding of the invention may be had from the following description of a preferred embodiment, given by way of example and to be understood in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a block diagram of the existing OMA DRM 2.0 functional architecture; 
         FIG. 2  is a flow diagram of the existing OMA DRM 2.0 ROAP 4-pass registration protocol; 
         FIG. 3  is a flow diagram of the existing OMA DRM 2.0 ROAP 2-pass RO acquisition protocol; 
         FIG. 4  is a flow diagram of the existing OMA DRM 2.0 ROAP 1-pass RO acquisition protocol; 
         FIG. 5  is a flow diagram of the existing OMA DRM 2.0 ROAP 2-pass join domain protocol; 
         FIG. 6  is a flow diagram of the existing OMA DRM 2.0 ROAP 1-pass leave domain protocol; 
         FIG. 7  is a block diagram of multi-party platform integrity checking among OMA DRM 2.0 entities; 
         FIG. 8  is a flowchart of a method for performing platform integrity verification between two entities where the two entities could be a device and an RI or a device and a CI; 
         FIG. 9  is a flow diagram of a 4-pass ROAP registration protocol for performing mutual platform integrity checking between a device and an RI using prior trust checking; 
         FIG. 10  is a flow diagram of a 4-pass ROAP registration protocol for performing mutual platform integrity checking between a device and an RI using modified Device Hello and RI Hello messages; 
         FIG. 11  is a flowchart of a method for performing DRM software integrity checking between two entities where the two entities could be a device and an RI or a device and a CI; 
         FIG. 12  is a flow diagram of a 2-pass ROAP RO acquisition protocol for performing mutual DRM software integrity checking between a device and an RI; and 
         FIG. 13  is a flow diagram of a method for improving the integrity of ROAP messages and processing using TCG techniques including sealed-binding and memory blobbing. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereafter, the term “wireless transmit/receive unit” (WTRU) includes, but is not limited to, a user equipment, mobile station, a fixed or mobile subscriber unit, a pager, or any other type of device capable of operating in a wired or wireless environment. When referred to hereafter, the term “base station” includes, but is not limited to, a Node B, a site controller, an access point, or any other type of interfacing device in a wireless environment. 
     The present invention discloses methods whereby information regarding the trust state or the integrity of a DRM entity (e.g., the device, the RI, or the CI) is explicitly and mutually requested and exchanged between any two DRM entities as a pre-requisite to the OMA DRM procedures. 
     A general architecture  700  of this method is shown in  FIG. 7 . The architecture includes four DRM entities: a device  702 , an RI  704 , a CI  706 , and a Private Certification Authority (PCA)  708 . The platform integrity checking assumes that the PCA  708  has records of the trusted computing (e.g., TCG) credentials for the other DRM entities (e.g., the device  702 , the RI  704 , and the CI  706 ), and provides a root of trust for certification of the TCG credentials. 
     Any pair of entities (e.g., the device  702  and the RI  704 , the device  702  and the CI  706 , or, the RI  704  and the CI  706 ) that want a mutual platform integrity check between themselves are trusted computing capable (e.g., are equipped with TCG Trusted Processing Modules (TPMs)  710 ). This implies that the trusted computing capable DRM entity not only have a TPM  710  (or an equivalent) but also related TCG resources such as the AIK  712 , the SML  714 , and protected memory using blobs  716 . Also present are OS or platform software  718  and DRM software  720 . 
     When the above requirements are met, any pair of different DRM entities can mutually check their platform integrity or platform trusted state using the PCA  708  and the trusted computing capabilities. As an example, the procedures for mutual integrity checking between the device  702  and the RI  704  are as follows. 
     The device  702 , the RI  704 , and the CI  706  are all capable of performing a self-check of the OS or other platform software components (step  730 ) and a self-check of the DRM software (step  732 ). The self-checks can be requested as part of a larger verification process (as discussed in greater detail below) or can be standalone processes. If either of the self-checks were to fail, that could be an indication that the entity has been compromised and should not be trusted. 
     The device  702  sends information about its platform TCG credentials to the RI  704  (step  740 ). Examples of the platform TCG credentials include, but are not limited to, a signed TCG platform certificate or a signed TPM certificate. As part of the credentials, the device  702  can also send the RI  704  a self-attested Trusted State or Platform Integrity Checked flag as supplemental information. If the device  702  is going to verify the platform integrity of the RI  704 , the credential information sent in step  740  will also include an indication by the device  702  that it wants the RI  704  to initiate procedures to verify its platform integrity. It is noted that the device  702  will be able to make a decision regarding whether to verify the platform integrity of the RI  704  only if the verification of the RI&#39;s platform integrity status is an optional feature; in one embodiment, verifying the RI&#39;s platform integrity is a mandatory feature. 
     Upon receiving the credential information from the device  702 , the RI  704  relays the credential information to the PCA  708  (step  742 ) and also requests the PCA  708  to verify the credentials about the device  702 , especially the device&#39;s most current trustworthiness. The PCA  708  then sends the most current trustworthiness information (e.g., platform trust level, etc.) regarding the device  702  to the RI  704  (step  744 ). Upon receipt of the device platform trustworthiness information from the PCA  708 , and also optionally the supplemental information from the device  702 , the RI  704  evaluates the trust level of the device  702 . The RI  704  decides whether to impart sufficient trust on the device platform&#39;s integrity to proceed further with the DRM procedures such as the registration protocol or RO acquisition protocol. 
     The device  702 , either as a mandatory procedure or as an optional procedure, can evaluate the platform integrity of the RI  704  in similar and reciprocal ways as in the steps  740 - 744 . More specifically, the RI  704  sends information about its platform TCG credentials to the device  702  (step  750 ). As part of the credentials, the RI  704  can also send the device  702  a self-attested Trusted State or Platform Integrity Checked flag as supplemental information. 
     Upon receiving the TCG-related information from the RI  704 , the device  702  relays the information to the PCA (step  752 ) and also requests the PCA  708  to verify the credentials about the RI  704 , especially the RI&#39;s most current trustworthiness. The PCA  708  then sends the most current trustworthiness information regarding the RI  704  to the device  702  (step  754 ). Upon receipt of the RI platform trustworthiness information from the PCA  708  regarding the RI  704 , and also optionally the supplemental information from the RI itself, the device  702  evaluates the trust level of the RI  704 . The device  702  decides whether to impart sufficient trust on the RI platform&#39;s integrity to proceed further with the DRM procedures such as the registration protocol or RO acquisition protocol. 
     The device  702 , either as a mandatory procedure or as an optional procedure, can evaluate the platform integrity of the CI  706 . The CI  706  sends information about its platform TCG credentials to the device  702  (step  760 ). As part of the credentials, the CI  706  can also send the device  702  a self-attested Trusted State or Platform Integrity Checked flag as supplemental information. 
     Upon receiving the TCG-related information from the CI  706 , the device  702  relays the information to the PCA (step  762 ) and also requests the PCA  708  to verify the credentials about the CI  706 , especially the CI&#39;s most current trustworthiness. The PCA  708  then sends the most current trustworthiness information regarding the CI  706  to the device  702  (step  764 ). Upon receipt of the CI platform trustworthiness information from the PCA  708  regarding the CI  706 , and also optionally the supplemental information from the CI itself, the device  702  evaluates the trust level of the CI  706 . The device  702  decides whether to impart sufficient trust on the CI platform&#39;s integrity to proceed further with the DRM procedures. 
     The platform integrity of the device  702  can be verified by the CI  706  as follows. The device  702  sends information about its platform TCG credentials to the CI  706  (step  770 ). As part of the credentials, the device  702  can also send the CI  706  a self-attested Trusted State or Platform Integrity Checked flag as supplemental information. If the device  702  is going to verify the platform integrity of the CI  706 , the credential information sent in step  770  will also include an indication by the device  702  that it wants the CI  706  to initiate procedures to verify its platform integrity. It is noted that the device  702  will be able to make a decision regarding whether to verify the platform integrity of the CI  706  only if the verification of the CI&#39;s platform integrity status is an optional feature; in one embodiment, verifying the CI&#39;s platform integrity is a mandatory feature. 
     Upon receiving the credential information from the device  702 , the CI  706  relays the credential information to the PCA  708  (step  772 ) and also requests the PCA  708  to verify the credentials about the device  702 , especially the device&#39;s most current trustworthiness. The PCA  708  then sends the most current trustworthiness information regarding the device  702  to the CI  706  (step  774 ). Upon receipt of the device platform trustworthiness information from the PCA  708 , and also optionally the supplemental information from the device  702 , the CI  706  evaluates the trust level of the device  702 . The CI  706  decides whether to impart sufficient trust on the device platform&#39;s integrity to proceed further with the DRM procedures. 
     It is noted that in the above example, steps  740 - 744 , for the device  702  to verify its integrity status to the RI  704 , are a mandatory feature of the present invention. However, verifying the platform integrity of either the RI  704  to the device  702  (steps  750 - 754 ), verifying the platform integrity of the CI  706  to the device  702  (steps  760 - 764 ), and verifying the device platform integrity to the CI  706  (steps  770 - 774 ) are optional, yet highly recommended, features in a DRM system. 
     It is also noted that these procedures need not be initiated by an active initiation by the entity that needs to be verified. The integrity verification procedures could start with a request by the entity wishing to verify the integrity of the other party. In such cases, steps  740 ,  750 ,  760 , or  770  would each be preceded by another step, whereby the entity wishing the verification of the platform integrity of the other party calls or requests the other party to send relevant trust-related information. 
     In an alternate embodiment, for a practical OMA DRM system implementation, the conditions or trigger mechanisms for the proposed platform integrity verification procedures described above may include the following. 
     1. The device platform integrity verification procedures (i.e., steps  740 - 744 ), could be performed by one or more of the following. 
     1A. Before a device wishes to initiate a new 4-pass ROAP registration protocol. 
     1B. Once per each RI, before the first registration with the particular RI takes place. In this case, the RI will receive the device&#39;s TCG credentials once before the first registration, and then the RI protects the device&#39;s credential information under its own TPM by binding the credential information with a TPM key. The RI then later unbinds the stored TCG credential and verifies, either periodically or upon some events, whether the device&#39;s TCG credential that it has received is still valid, e.g., by consultation with a OCSP CA. 
     1C. Periodically, every time a specified time duration, for example, T DEV-PLATFORM-LAST-REG , has elapsed since the device completed the last registration protocol with the same RI. 
     1D. Periodically, every time a specified time duration, for example, T DEV-PLATFORM-LAST-REPORT , has elapsed since the last time the device had verified its platform integrity status to the same RI. 
     2. If and when the RI platform integrity verification procedures (i.e., steps  750 - 754 ) are implemented, they could be performed by one or more of the following. 
     2A. Once per each device, before the first registration with the particular device takes place. In this case, the device will receive the RI&#39;s TCG credentials once before the first registration, and then the device protects the RI&#39;s credential information under its own TPM by binding the credential information with a TPM key. The device then later unbinds the stored TCG credential and verifies, either periodically or upon some events, whether the RI&#39;s TCG credential that it has received is still valid, e.g., by consultation with an OCSP CA. 
     2B. Anytime an RI receives an indication from the device that the device wishes the RI to verify its integrity status to the device, either as a standalone message or as part of a modified ROAP protocol message. 
     2C. Periodically, every time a specified secure time duration has elapsed, for example, T RI-PLATFORM-LAST-REPORT  has elapsed since the last time the RI has verified its integrity status to the device. 
     3. As for the platform integrity verification between a device and a CI, mechanisms similar to the above can be considered for periodic and/or event-driven occurrence of the integrity verification process. Also, in the case of the device&#39;s verification of the CI&#39;s platform integrity, it could also be performed every time before content has to be purchased or downloaded, and possibly vice versa (i.e., the device&#39;s platform integrity has to be verified to the CI). 
     The prior art has considered use of a “secure boot-up” using TCG techniques coupled with the application of robust DRM. In such schemes, the platform&#39;s OS and other boot-up related code are integrity-checked whenever a device is booted, implicitly performing a platform integrity check before any DRM application can be run. The present invention provides a more systematic and explicit use of the boot-time platform integrity check, as well as platform integrity checks at other times based on pre-determined periods of time as well as upon the occurrence of certain events. The present invention also generalizes platform integrity checking from the device to the RI and the CI as well. The continuous platform integrity checks are beneficial due to the fact that just because a device has correctly received a particular valid CO, it doesn&#39;t mean that the RI or the CI should be considered trustworthy indefinitely into the future from that time. A periodic and/or event-driven continual verification of the trustworthiness provides a good protective mechanism. 
     Also, as for the need for the integrity checking between the device and the CI, even if the content arrives before an RO, the content may be compromised when the integrity of the CI&#39;s platform or the CI&#39;s DRM SW is compromised. For example, suppose a user has downloaded a file. Even when the RO has not yet been acquired, a user may inadvertently click on the content or may perform a validity check on the content. If the content was compromised (e.g., has a virus attached to it) the content, even without an RO, could do damage to the device. Also, in the pre-download interactions between the device and a CI (for example, during the discovery phase), a compromised device can do harm to a CI, for example, by adding a virus attached to the content to a message intended for the CI. In addition, from a business perspective, a CI would not want to send content to a compromised device; for example, a compromised device could redistribute content for free to unauthorized recipients. The mutual platform (and SW) integrity verification between a device and a CI thus have merits in protecting the entire system. 
     It is also noted that there can be several different ways to embody the central ideas outlined in the above architectural discussions. Two such examples are discussed below, but it is noted that these are only illustrative examples of the broader concepts based on the architecture described in the above paragraphs. 
     Platform Integrity Verification 
       FIG. 8  is a flowchart of a method  800  for performing platform integrity verification between two entities. The two entities can be a device and an RI, a device and a CI, or an RI and a CI. The method  800  utilizes a requesting entity (RE) and a target entity (TE); it is noted that either entity of the pair (device, RI, or CI) can be the RE. The method  800  operates in the same manner regardless of which entity is the RE and which entity is the TE. 
     The method  800  begins with the RE sending a request to the TE to report its platform integrity status (step  802 ). In response to the request, the TE send its TCG credentials to the RE (step  804 ). The TCG credentials can include, for example, platform credentials, TPM credentials, or conformance credentials. The RE then sends the TE&#39;s TCG credentials to an OCSP Responder for verification of the credentials (step  806 ). The OCSP Responder reviews the TE&#39;s TCG credentials and reports the verification status to the RE (step  808 ). 
     The RE sends a request to the TE to report its own platform integrity status (step  810 ). The TE checks its platform integrity status (step  812 ), sends a platform integrity status flag to the RE (step  814 ) and the method terminates (step  816 ). 
     The method  800  can be applied either without changes to the ROAP protocols (discussed below in connection with  FIG. 9 ) or with changes to the ROAP protocols (discussed below in connection with  FIG. 10 ). 
     Integrity Verification Without Changes to the ROAP Protocols 
       FIG. 9  is a flow diagram of a method  900  to exchange integrity-related information between a device  902  and an RI  904  using TCG techniques (i.e., utilizing an OCSP responder/PCA  906 ) separately from the ROAP protocol. It is noted that in the method  900 , the same entity  906  is depicted as being both a PCA for the DRM processing as well as an OCSP responder for TCG processing. In the method  900 , the platform integrity verification (as shown by the dashed rectangle) is performed prior to the ROAP 4-pass registration protocol. Performing platform integrity verification before the registration protocol is useful because the registration protocol is not frequently performed and the platform integrity verification process takes some time to complete; if the platform integrity verification were performed with each message, the overall operation of the system could be unnecessarily slowed. A person skilled in the art could assume that after the platform integrity verification is performed, that only one Device Hello message would be received by the RI, as it would indicate a trusted device. If more than one Device Hello message were received by the RI from the same device, it could be an indication of a DoS attack. Platform integrity verification could also be performed in connection with the authentication protocol and the object acquisition protocol. 
     The device  902 , prior to initiating the 4-pass registration protocol with the RI  904 , starts a separate set of procedures with the RI  904  to perform mutual verification of platform integrity. The device  902  first sends its own TCG credentials (e.g., platform credentials, TPM credentials, conformance credentials, etc.) or other information including or related to the TCG credential, to the RI  904  (step  910 ). Optionally, the device  902  also sends a request to the RI  904  to check and report its own platform integrity status to the device  902 ; this request is included with the device credentials. 
     The RI  904  requests the PCA  906  to verify the device&#39;s TCG credentials (step  912 ). The PCA  906  responds to the RI&#39;s request and sends information on the device&#39;s TCG credential (step  914 ). 
     The RI  904  requests the device  902  to report its platform integrity status flag (step  916 ). Also, if the device  902  has requested that the RI  904  verify and report its platform integrity status in step  910  and if the RI  904  wishes to and is able to oblige to the request, the RI  904  sends its own TCG credential or other information including or related to the TCG credential, to the device  902  in step  916 . If the RI  904  cannot or does not wish to oblige to the request, it sends a “not obliging” message to the device. The RI  904  may not respond to the request for a number of reasons, including a resource limited RI (i.e., the RI does not have sufficient available resources to respond to the request) or the device credibility check fails. The device may abort the protocol depending on the confidence level that the device has with the RI; if the device trusts the RI, it would likely continue with the protocol even if the RI refused to respond to the request. Upon receiving the request from the RI  904  to check the platform status, the device  902  checks its own platform integrity status (step  918 ). 
     The device  902  requests the PCA  906  to verify the RI&#39;s TCG credential (step  920 ). The PCA  906 , upon such receiving the request form the device  902 , returns information on the RI&#39;s TCG credential (step  922 ). The device  902  sends its platform integrity status flag to the RI  904  (step  924 ). If the RI  904  received a request from the device  902  to check its integrity status, and if the RI  904  wishes to and is able to oblige to the request, the RI  904  checks its own platform integrity (step  926 ). The RI then returns its platform integrity status flag to the device  902  (step  928 ). The optional steps regarding the RI integrity check can be performed in any order; those steps do not need to be intertwined with the device integrity check as shown in  FIG. 9 . In addition, the RI can initiate its own integrity check. Also, if RI refuses to fully respond to the request with its own TCG credential information for any of the possible reasons, it may indicate such fact to the device in an appropriate way, for example in step  922 . 
     The method  900  enables the device  902  and the RI  904  to achieve mutual platform integrity verification. Upon such verification, the device can then start the ROAP registration protocol. The steps of the registration protocol (steps  930 - 940 ) shown in  FIG. 9  are the same as steps  210 - 220  of the method  200  described above. It is also noted that these procedures can be triggered or repeated at periodic intervals. 
     Integrity Verification with Changes to the ROAP Registration Protocol 
       FIG. 10 , in another exemplary embodiment, shows a method  1000  in which a device  1002  and an RI  1004  exchange integrity-related information, also utilizing the services of an OCSP responder/PCA  1006 . In the method  1000 , the existing Device Hello and RI Hello messages of the ROAP registration protocol are modified to convey both the TCG credential and the request to the other party for platform integrity verification. 
     The device  1002  sends a modified Device Hello message to the RI  1004  (step  1010 ), the message including the device TCG credential and an optional request to the RI  1004  to report its platform integrity. The RI  1004  forwards the device credentials to the PCA  1006  for verification (step  1012 ). The PCA  1006  then returns the device TCG credentials to the RI  1004  (step  1014 ). The RI  1004  responds to the device  1002  with a modified RI Hello message (step  1016 ), the message optionally including the RI&#39;s TCG credential. 
     Next, the device  1002  optionally sends a request to the PCA  1006  to check the RI&#39;s TCG credential (step  1018 ). The PCA  1006  checks the RI&#39;s credentials and reports the result back to the device  1002  (step  1020 ). The device  1002  checks its own integrity status (step  1022 ) and reports the integrity status to the RI  1004  (step  1024 ). 
     If the device  1002  has requested that the RI  1004  report its integrity status, the RI  1004  performs a platform integrity check (step  1026 ) and reports the integrity status, e.g., its trusted state flag, back to the device  1002  (step  1028 ). The steps  1030 - 1036  are the same as steps  214 - 220  as shown in  FIG. 2  of the ROAP registration protocol. 
     Checking the Integrity of the DRM Software 
       FIG. 11  is a flowchart of a method  1100  for checking the integrity of the DRM SW (e.g., the DRM user agent SW residing at the device or the DRM SW residing at the RI or the CI) among any pair of DRM entities. A requesting entity (RE) sends a request to a target entity (TE) to perform a DRM SW integrity check (step  1102 ). The TE checks its DRM SW integrity (step  1104 ), sends a DRM SW integrity status flag to the RE (step  1106 ), and the method terminates (step  1108 ). It is noted that when the TE is a device, the integrity of the device drivers and media player SW can be checked separately from the integrity of the DRM SW, if these two components exist separately on the device. 
     The method  1100  relates only to the RE obtaining a DRM SW integrity check from the TE. To perform mutual DRM SW integrity checking, the method  1100  would need to be performed twice, once from the RE to the TE and then from the TE to the RE (with the RE and the TE switching roles). During a mutual DRM SW integrity check, the requests can be intertwined (as shown in  FIG. 12 ) or can be separated as shown in  FIG. 11 . The operation of the method does not change if a mutual DRM SW integrity check is being performed. 
     The OMA DRM 2.0 specification assumes, without suggesting how such assumptions can be validly implemented, that the DRM user agent SW (or the device DRM SW, in the terminology used in the present invention) as well as the RI (or the RI&#39;s DRM SW) can be implicitly trusted. The authentication protocol in the OMA DRM 2.0 specification thus only specifies the actual authentication procedures between entities that are already considered trustworthy. For obvious reasons, this implicit SW trust assumption in practice cannot be automatically assumed, without actual steps to implement and verify them. The methods described in this section concern such concrete steps. 
       FIG. 12  is a flow diagram of a method  1200  for applying the DRM SW check in connection with the ROAP RO acquisition protocol. The method  1200  utilizes a device  1202 , an RI  1204 , and an OCSP responder/PCA  1206 . First, the PCA  1206  communicates with the device  1202  and the RI  1204  to perform platform integrity checking and the ROAP registration protocol (step  1210 ). The device  1202  and the RI  1204  perform a mutual platform integrity check, a unidirectional DRM SW integrity check, or a mutual DRM SW integrity check (step  1212 ). 
     The RI  1204  sends a request to the device  1202  to check and report the device&#39;s DRM user agent (UA) SW integrity (step  1214 ). The device  1202  checks its latest DRM UA SW integrity (step  1216 ). The device  1202  optionally sends a request to the RI  1204  to check and report the RI&#39;s DRM SW integrity (step  1218 ). If requested, the RI  1204  checks its latest DRM SW integrity (step  1220 ). The device  1202  sends a device DRM SW integrity status flag to the RI  1204  (step  1222 ). If previously requested, the RI  1204  sends an RI DRM SW integrity status flag to the device  1202  (step  1224 ). It is noted that the steps of the optional RI integrity check can be performed in any order and need not be intertwined with the device integrity check as shown in  FIG. 12 . 
     It is noted that the method  1200  can be generalized for mutual DRM SW integrity verification between a device and a CI, instead of the illustrated device/RI interaction. Upon completion of steps  1210 - 1224 , the device  1202  can start, for example, the 2-pass RO acquisition protocol in steps  1226  and  1228 , which are the same as steps  310  and  312  as described above in connection with  FIG. 3 . It is further noted that although the method  1200  is shown in conjunction with the RO acquisition protocol, it can be used in conjunction with any other ROAP protocol, but to minimize the overhead associated with the method  1200 , it could be performed with only an appropriately selected subset of ROAP protocols at any given time. For a practical OMA DRM system implementation, some of the conditions or trigger mechanisms for the proposed platform and/or DRM SW integrity verification procedures described above may include: 
     1. The device DRM SW integrity verification procedures can be triggered by one or more of the following. 
     1A. Before a device wishes to initiate a new 2-pass ROAP registration protocol, 2-pass join domain protocol, or the 2-pass leave domain protocol. 
     1B. Periodically, every time a specified time duration, for example T DEV-DRM-LAST-ROAP , has elapsed since the device last completed the 2-pass ROAP registration protocol, 2-pass join domain protocol, or the 2-pass leave domain protocol with the same RI. 
     1C. Periodically, every time a specified time duration, for example T DEV-DRM-LAST-REPORT , has elapsed since the last time the device had verified and reported its DRM SW integrity status to the same RI. 
     1D. Whenever a device updates its DRM SW. 
     1E. Whenever the platform SW is updated or changed. 
     2. The RI DRM integrity verification procedures could be performed by one or more of the following. 
     2A. Anytime an RI receives an indication from the device that the device wishes the RI to verify its DRM SW integrity status to the device, either as a standalone message or as part of a modified ROAP protocol message. 
     2B. Periodically, every time a specified time duration, for example T RI-DRM-LAST-REPORT , has elapsed since the last time the RI has verified and reported its DRM SW integrity status to the device. 
     2C. Whenever an RI has updated its DRM SW. 
     2D. Every time before the device sends an RO request, in cases where the user is obtaining content on a frequent basis, such as with streaming content. 
     As for the platform integrity verification between a device and a CI, mechanisms similar to the above can be considered for periodic and/or event-driven occurrence of the DRM SW integrity verification process. 
     The proposed methods for DRM platform verification and DRM SW verification can be performed independently of each other, but it is also contemplated that these verification procedures can be combined as part of a group of procedures. In such an embodiment, the DRM platform verification steps are considered a pre-requisite for the DRM SW verification steps. For example, for integrity verification between a device and an RI, the device and the RI first establish the trust on each other&#39;s entire platform by performing the DRM platform verification procedures as described above. The trigger mechanisms include the general platform verification trigger conditions. Then, as the conditions for the DRM SW verification trigger arise, the DRM SW verification procedure follows. Note that both types of verification procedures will execute when their respective trigger conditions are met. However, the DRM SW verification steps will be mastered to the successful completion of the DRM platform verification steps, i.e., if the DRM platform verification fails between a device and an RI, further processing in the DRM SW verification as well as actual DRM ROAP processing and usage-related processing will fail. 
     Sealed-Signing and Binding 
     The OMA DRM 2.0 specification&#39;s existing mechanisms to protect the integrity of the ROAP protocol is limited to including digital signatures (or message integrity checking) in some, but not all, of the ROAP messages. Given that the ROAP protocol is of central importance in the secure DRM processing implementation, it is important to safeguard and continually verify the integrity of the information that is used and exchanged in the ROAP protocol. 
     Therefore, in an alternate embodiment of the present invention, methods are disclosed to strengthen the integrity of the ROAP protocol whereby information central to a reliable authentication and integrity verification between the DRM device and an RI can: (1) be safely stored using TCG techniques, and (2) be pre-verified before being transmitted to the other side or before being used for processing at the side where the information is stored. 
     This method involves two basic procedures that use the TCG techniques of sealed-signing (i.e., symmetrically encrypt target information and then asymmetrically sign the symmetric key plus a set of PCR values that indicate the then-current integrity status of either the platform or specific SW components) and binding (asymmetrically encrypt target information with a key whose private decrypting key is kept in a protected module such as a TPM). Sealed-signing imparts the highest level of information security provided by asymmetric encryption, digital signatures, and binding to a trusted state of the device DRM user agent SW as indicated by the protected PCR values. Binding imparts a high level of protection using asymmetric encryption where the decryption key is protected inside the TPM. 
     The following systematic principles use sealed-signing and binding to protect both the confidentiality and the integrity of the information that is used in the ROAP messages, and thereby indirectly enhance the strength of the integrity of the ROAP protocols themselves. In the following discussion, both the device and the RI (or the portion of the RI that deals with this specific device) are assumed to be equipped with a TPM and support full TPM functionality. 
     The device and the RI can each set aside and use a set of two storage keys to cryptographically bind and securely store certain information related to ROAP processing to the trusted platform on which the device or the RI resides. For the device, these keys are K_DEV_BIND_A and K_DEV_BIND_B. For the RI, these keys are K_RI_BIND_A and K_RI_BIND_B. These are TPM-maintained asymmetric keys (i.e., encryption is done with public key and decryption is done with private key protected inside a TPM). 
     The device and the RI each use either a single PCR or a set of PCRs for DRM processing. The device and the RI also set aside and use an Attestation Identity Key (AIK) to sealed-sign certain information related to ROAP processing to the trusted platform and its particular PCR values. It is noted that the TCG AIK keys are used only for signing PCR values. For the device, its AIK is K_DEV_AIK and for the RI, its AIK is K_RI_AIK. Also, the sealed-signing requires an asymmetric storage key for the encryption operation of the target data. The device and the RI thus each set aside and use a storage key for this purpose. The storage key for the device is K_DEV_STO_SEAL, and the storage key for the RI is K_RI_STO_SEAL. 
     The method then uses a combination of sealed-signing and binding with an added measure of protecting confidentiality as well as integrity to enhance the strength of storing the various information elements involved in the ROAP processing. For example,  FIG. 13  is a flow diagram of a method  1300  in which TPM sealed-signing and binding operations are used to protect the confidentiality and integrity of information in the various messages that comprise the 4-pass ROAP registration protocol. In the method  1300 , a device  1302  and an RI  1304  each sealed-sign a selective set of ROAP-related information and bind the information using two sets of storage keys that each either transmits (to the other side) or receives (from the other side) during the course of the 4-pass registration protocol. 
     The device  1302  first sealed-signs the device ID information element (which, in the OMA DRM case is the SHA-1 hash of the OMA DRM public key) with the encryption key K_DEV_STO_SEAL and the device-specific AIK K_DEV_AIK (step  1310 ). This information is bound (using asymmetric encryption) to other information intended for the Device Hello message with the storage key K_DEV_BIND_A (step  1310 ). The Device Hello message is then sent from the device  1302  to the RI  1304  (step  1312 ). 
     By sealed-signing information such as the device ID and binding the other information comprising the Device Hello message, the device  1302  could institute a policy that the Device Hello message will be transmitted only when and if the device  1302  recovers (i.e., unsealed-signs and unbinds) the previously sealed-signed and bound information from their protected storage, compares them to the current values of such information elements that the DRM SW may be using, and verifies the genuineness and integrity of the current values. It is noted that the choice of the information elements to be sealed-signed versus bound in this scenario is given just as an example. Other information elements may be sealed-signed and bound in different combinations without effecting the operation of the present invention. Other combinations can be derived from items such as system time, any information element in a message, algorithms, and nonces. One reason for securing the nonces is to determine whether the nonces are truly random, as some random number generators especially ones that may be harmfully compromised, may repeat the same pattern and generate the same numbers as their outputs in unacceptably short periods of time. 
     The RI  1304 , upon receipt of the Device Hello message, binds the information contained in the Device Hello message with its binding key, K_RI_BIND_A (step  1314 ). This step allows secure, integrity-protected storage of the key information that the RI  1304  received from the device  1302 . Alternatively, the RI  1304  can also extract the device ID (or any other information element) from the Device Hello message and sealed-sign that information element separately using the AIK K_RI_AIK and the encryption key K_RI_STO_SEAL. 
     The RI  1304  sealed-signs the RI ID and the RI URL information elements with the encryption key K_RI_STO_SEAL and the AIK K_RI_AIK (step  1316 ). The RI  1304  also binds the other information contained in its RI Hello message with the storage key K_RI_BIND_A (step  1316 ). The RI  1304  then sends the RI Hello message to the device  1302  (step  1318 ). 
     The RI  1304  transmits the RI Hello message to the device  1302  only when and if the RI  1304  first recovers (i.e., unsealed-signs and unbinds) the previously sealed-signed and bound information from the protected storage, compares them to the current values of such information elements that the RI DRM SW may be using, and verifies the genuineness and integrity of the current values. 
     The device  1302 , upon receipt of the RI Hello message, binds the information contained in the RI Hello message with the second binding key, i.e., K_DEV_BIND_B (step  1320 ). This step allows secure, integrity-protected storage of the key information that the device received from the RI  1304 . Alternatively, the device  1302  can also extract selected information elements from the received RI Hello message (such as the RI ID and/or the RI URL) and sealed-sign them using the AIK K_DEV_AIK and the encryption key K_DEV_STO_SEAL, while simply binding the rest of the information received in the RI Hello message using K_DEV_BIND_B. 
     The device  1302  sealed-signs the certificate chain, the DCF hash, and the Request Time with K_DEV_AIK and K_DEV_STO_SEAL (step  1322 ). The device  1302  then binds the other information intended for the Registration Request message with K_DEV_BIND_A (step  1322 ). The device  1302  then sends the Registration Request message to the RI  1304  (step  1324 ). The device  1302  only sends the Registration Request message if the device recovers (i.e., unseal-signs and unbinds) the previously sealed-signed and bound information, compares the recovered values to the current temporary values used in the DRM SW memory, and verifies the genuineness and integrity of the current values. Upon receipt of the Registration Request message, the RI  1304  binds the information from the Registration Request message with the binding key K_RI_BIND_B (step  1326 ). 
     The RI  1304  sealed-signs the keys, the certificate chain, and the ROs with K_RI_AIK and K_RI_STO_SEAL (step  1328 ). The RI  1304  then binds this with other information to be included in the Registration Response message with the binding key K_RI_BIND_A (step  1328 ). The RI  1304  then sends the Registration Response message to the device  1302  (step  1330 ). The RI  1304  only sends the Registration Response message if the RI recovers (i.e., unseal-signs and unbinds) the previously sealed-signed and bound information, compares the recovered values to the current temporary values used in the DRM SW memory, and verifies the genuineness and integrity of the current values. Upon receipt of the Registration Response message, the device  1302  binds the RI-generated information from the Registration Response message with the binding key K_DEV_BIND_B (step  1332 ). 
     It is noted that the sealed-signing and binding can be used with any other ROAP protocol. The method  1300  described above is exemplary, and its principles can be equally applied to any other ROAP protocol. 
     Data obtained during the OMA DRM ROAP message exchanges will need to be un-sealed and re-sealed to a new configuration PCR value, if the entity that sealed or sealed-signed the data has updated either its platform OS or the DRM SW. When such an event occurs, the DRM ROAP-related data that had been sealed or sealed-signed to a particular state (or, equivalently, to a particular set of PCR values) will have to be first un-sealed and then re-sealed to the most current state of the updated platform OS. There are existing techniques in the prior art that address this procedural requirement and it is assumed that such procedures will take place to ensure proper un-sealing and re-sealing of any DRM ROAP-related data that is stored using sealing or sealed-signing as proposed herein. 
     One additional enhancement is to add a field to the existing ROAP message formats to indicate the TCG capability of the sending device. The TCG capability field can assist in increasing interoperability with legacy devices by making an early determination whether the receiving entity can support TCG related information and procedures. 
     Modification of the Device Hello Message and Its Derivation 
     A first modification is to add a new device TPM Capability Indication (DTCI), which is an indicator of the device&#39;s TPM capability in either a new element of the existing Extension parameter of the Device Hello message, or alternatively and preferably, add the DTCI as a new first parameter in the header of the Device Hello message. The DTCI can be either one bit (indicating either the absence or the presence of a device TPM) or a few bits (indicating more granular information on the device&#39;s TPM capability). If the DTCI is inserted as a new parameter, it preferably should be inserted as the first parameter, before the device ID parameter, so that the RI can know in advance of other parameters that the device has certain TPM capabilities and process the information from the later parameters (e.g., the device ID) utilizing the DTCI. The benefit of the DTCI information is that it allows the RI to evaluate the trustworthiness of the device in its further interaction with the device in the remainder of the ROAP protocols. 
     A second modification is to use the device-specific TCG EK credential or the TCG AIK credential to hash and derive the DRM device ID. The benefit of this modification is that the EK credential and/or the AIK credential is highly protected by the TPM inside the device, and thus, deriving the DRM device ID from either of these credentials strengthens the integrity of the DRM device ID information. 
     A third modification is to add a new signature parameter where the Device Hello message, up to but excluding the signature, is signed with the device&#39;s AIK private key, intended to be verified by the RI. The benefit of this modification is to protect the integrity of the device TPM capability from the first interaction between the device and the RI. The use of the device&#39;s AIK private key, which is highly securely protected by the TPM, strengthens the integrity of the signing operation. 
     Tables 12 and 13 show two possible formats for the modified Device Hello message. Tables 12 shows the format of a message with the DTCI bit as the first parameter. Table 13 shows the format of the Device Hello message where the DTCI is a new element of the existing Extension parameter. 
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 12 
               
             
             
               
                   
               
               
                 Modified Device Hello message format with a separate DTCI parameter 
               
             
          
           
               
                   
                 Mandatory 
                 Notes (Changes from OMA DRM 2.0 ROAP Device 
               
               
                 Parameter 
                 or Optional 
                 Hello message) 
               
               
                   
               
               
                 Device TPM 
                 Optional 
                 New Parameter: Either a 1-bit indicator (for absence 
               
               
                 Capability 
                   
                 or presence of a device TPM) or more bits indicating 
               
               
                 Indicator 
                   
                 more granular information about the device TPM 
               
               
                 (DTCI) 
                   
                 capability. 
               
               
                 Version 
                 Mandatory 
                 Unchanged. 
               
               
                 Device ID 
                 Mandatory 
                 Unchanged in format, but uses the SHA-1 hash 
               
               
                   
                   
                 computed by the device TPM of either the device 
               
               
                   
                   
                 TPM&#39;s EK credential or one of the device TPM&#39;s AIK 
               
               
                   
                   
                 credentials. 
               
               
                 Supported 
                 Optional 
                 Unchanged. 
               
               
                 Algorithms 
               
               
                 Extensions 
                 Optional 
                 Unchanged. 
               
               
                 Signature 
                 Mandatory 
                 New parameter: Signature using the RSA-PSS 
               
               
                   
                   
                 algorithm on the Device Hello message up to and 
               
               
                   
                   
                 excluding the Signature parameter, signed by one of 
               
               
                   
                   
                 the device&#39;s AIK private keys for which the RI has pre- 
               
               
                   
                   
                 acquired the public key. 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 13 
               
             
             
               
                   
               
               
                 Modified Device Hello message format, with DTCI in the Extensions 
               
             
          
           
               
                   
                 Mandatory 
                 Notes (Changes from OMA DRM 2.0 ROAP Device 
               
               
                 Parameter 
                 or Optional 
                 Hello message) 
               
               
                   
               
               
                 Version 
                 Mandatory 
                 Unchanged. 
               
               
                 Device ID 
                 Mandatory 
                 Unchanged in format, but uses the SHA-1 hash 
               
               
                   
                   
                 computed by the device TPM of either the device 
               
               
                   
                   
                 TPM&#39;s EK credential or one of the device TPM&#39;s AIK 
               
               
                   
                   
                 credentials. 
               
               
                 Supported 
                 Optional 
                 Unchanged. 
               
               
                 Algorithms 
               
               
                 Extensions 
                 Optional 
                 All of the OMA DRM 2.0 ROAP Device Hello 
               
               
                   
                   
                 Extensions elements, plus the DTCI element 
               
               
                   
                   
                 consisting of one or more bits indicating the device&#39;s 
               
               
                   
                   
                 TPM capability. 
               
               
                 Signature 
                 Mandatory 
                 New parameter: Signature using the RSA-PSS 
               
               
                   
                   
                 algorithm on the Device Hello message up to and 
               
               
                   
                   
                 excluding the Signature parameter, signed by one of 
               
               
                   
                   
                 the device&#39;s AIK private keys for which the RI has pre- 
               
               
                   
                   
                 acquired the public key. 
               
               
                   
               
             
          
         
       
     
     Modification of the RI Hello Message and Its Derivation 
     A first modification is to add a new RI TPM Capability Indication (RTCI), which is an indicator of the RI&#39;s TPM capability either as a new element of the existing Extension parameter of the RI Hello message, or alternatively and preferably, add the RTCI as a new first parameter in the header of the RI Hello message. The benefit of this modification is that it allows the device to use the RTCI information to evaluate the trustworthiness of the RI and to utilize such information in its further interaction with the RI in the remainder of the ROAP protocol procedures. 
     A second modification is to use the RI TPM to provide a pseudo-random number for the session ID. The benefit of this modification is that the TPM provides a highly secure hardware-based pseudo-random number generator. Using the TPM to generate a pseudo-random number that is used as the session ID strengthens the security of the protocol. 
     A third modification is to use the RI TCG EK credential or the TCG AIK credential belonging to the RI&#39;s TPM to derive the RI ID. The benefit of this modification is that the EK credential and/or the AIK credential is highly protected by the TPM inside the device and deriving the DRM device ID from either of these credentials strengthens the integrity of the DRM device ID information. 
     A fourth modification is to use the RI TPM to provide the RI nonce. The benefit of this modification is that the TPM provides a highly secure hardware-based pseudo-random number generator. Using the TPM to generate the RI nonce strengthens the integrity of the nonce that is used in the RI Hello message. 
     A fifth modification is to include the device TCG credentials in the device trusted RI anchor. The device&#39;s TCG credentials include the EK credential, the AIK credential, the platform credential, and the compliance credentials that the RI has pre-acquired from a trusted TCG CA. The benefit of this modification is to enhance the trust that the device can have on the RI Hello message. 
     A sixth modification is to add a signature of the RI Hello message up to and excluding the signature signed with RI&#39;s AIK private key, where the RI&#39;s AIK public key has been previously distributed to the device as part of the RI Hello message. The benefit of this modification is to protect the integrity of the RTCI from the first interaction between the RI and the device. Using the RI&#39;s AIK private key, which is highly securely protected by the RI&#39;s TPM, strengthens the integrity of the signing operation. 
     Tables 14 and 15 show two possible formats for the modified RI Hello message. Table 14 shows the format of the RI Hello message with the RTCI bit as the first parameter. Table 15 shows the format of the RI Hello message where the RTCI is a new element of the existing Extension parameter. 
     
       
         
               
             
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 14 
               
             
             
               
                   
               
               
                 Modified RI Hello message format 
               
             
          
           
               
                   
                 ROAP-RI Hello 
                   
               
             
          
           
               
                   
                   
                 Status not 
                 Notes (Changes from OMA DRM 2.0 RI 
               
               
                 Parameter 
                 Status = “Success” 
                 “Success” 
                 Hello message) 
               
               
                   
               
               
                 RI TPM 
                 Optional 
                 Optional 
                 New Parameter: Either a 1-bit indicator 
               
               
                 Capability 
                   
                   
                 (for absence or presence of an RI TPM) or 
               
               
                 Indicator 
                   
                   
                 more bits indicating more granular 
               
               
                 (RTCI) 
                   
                   
                 information about the RI TPM capability. 
               
               
                 Status 
                 Mandatory 
                 Mandatory 
                 Unchanged. 
               
               
                 Session ID 
                 Mandatory 
                 — 
                 Unchanged in format, but generated by 
               
               
                   
                   
                   
                 the RI&#39;s TPM. 
               
               
                 Selected 
                 Mandatory 
                 — 
                 Unchanged. 
               
               
                 Version 
               
               
                 RI ID 
                 Mandatory 
                 — 
                 Unchanged in format but uses the SHA-1 
               
               
                   
                   
                   
                 hash generated by the RI&#39;s TPM of either 
               
               
                   
                   
                   
                 the RI TPM EK credential or one of the RI 
               
               
                   
                   
                   
                 TPM AIK credentials, using the RSA-PSS 
               
               
                   
                   
                   
                 method supported by the OMA DRM 2.0 
               
               
                   
                   
                   
                 ROAP. 
               
               
                 Selected 
                 Optional 
                 — 
                 Unchanged. 
               
               
                 Algorithm 
               
               
                 RI Nonce 
                 Mandatory 
                 — 
                 Unchanged in format, but to be generated 
               
               
                   
                   
                   
                 by the RI TPM if the RI TPM exists. 
               
               
                 Trusted device 
                 Optional 
                 — 
                 List of device trust anchors recognized by 
               
               
                 Authorities 
                   
                   
                 the RI. The proposed modification includes 
               
               
                   
                   
                   
                 the device&#39;s TCG credential(s) as part of 
               
               
                   
                   
                   
                 the list of trust anchors. 
               
               
                 Server Info 
                 Optional 
                 — 
                 Unchanged. 
               
               
                 Extensions 
                 Optional 
                 — 
                 Unchanged. 
               
               
                 Signature 
                 Mandatory 
                 Mandatory 
                 New parameter: Computed using the RSA- 
               
               
                   
                   
                   
                 PSS algorithm on the RI Hello message up 
               
               
                   
                   
                   
                 to and excluding the Signature parameter, 
               
               
                   
                   
                   
                 signed by one of the RI AIK private keys 
               
               
                   
                   
                   
                 for which the device has pre-acquired the 
               
               
                   
                   
                   
                 public key. The Signature is mandatory 
               
               
                   
                   
                   
                 regardless of the success or failure of the 
               
               
                   
                   
                   
                 Device Hello message. 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 15 
               
             
             
               
                   
               
               
                 Modified RI Hello message format 
               
             
          
           
               
                   
                 ROAP-RI Hello 
                   
               
             
          
           
               
                   
                   
                 Status not 
                 Notes (Changes from OMA DRM 2.0 RI 
               
               
                 Parameter 
                 Status = “Success” 
                 “Success” 
                 Hello) 
               
               
                   
               
               
                 Status 
                 Mandatory 
                 Mandatory 
                 Unchanged. 
               
               
                 Session ID 
                 Mandatory 
                 — 
                 Unchanged in format, but generated by 
               
               
                   
                   
                   
                 the RI&#39;s TPM. 
               
               
                 Selected 
                 Mandatory 
                 — 
                 Unchanged. 
               
               
                 Version 
               
               
                 RI ID 
                 Mandatory 
                 — 
                 Unchanged in format but uses the SHA- 
               
               
                   
                   
                   
                 1 hash computed by the RI&#39;s TPM of 
               
               
                   
                   
                   
                 either the RI TPM EK credential or one 
               
               
                   
                   
                   
                 of the RI TPM AIK credentials, using the 
               
               
                   
                   
                   
                 RSA-PSS method supported by the OMA 
               
               
                   
                   
                   
                 DRM 2.0 ROAP. 
               
               
                 Selected 
                 Optional 
                 — 
                 Unchanged. 
               
               
                 Algorithm 
               
               
                 RI Nonce 
                 Mandatory 
                 — 
                 Unchanged in format, but to be 
               
               
                   
                   
                   
                 generated by the RI TPM if the RI TPM 
               
               
                   
                   
                   
                 exists. 
               
               
                 Trusted device 
                 Optional 
                 — 
                 List of device trust anchors recognized 
               
               
                 Authorities 
                   
                   
                 by the RI. Proposed modification has 
               
               
                   
                   
                   
                 additional inclusion of the device&#39;s TCG 
               
               
                   
                   
                   
                 credential(s) as part of the list of the 
               
               
                   
                   
                   
                 trust anchors. 
               
               
                 Server Info 
                 Optional 
                 — 
                 Unchanged. 
               
               
                 Extensions 
                 Optional 
                 — 
                 All of the OMA DRM 2.0 ROAP RI Hello 
               
               
                   
                   
                   
                 Extensions elements, plus a new RI TPM 
               
               
                   
                   
                   
                 Capability Indicator (RTCI) element 
               
               
                   
                   
                   
                 consisting of one or more bits indicating 
               
               
                   
                   
                   
                 the RI&#39;s TPM Capability. 
               
               
                 Signature 
                 Mandatory 
                 Mandatory 
                 New parameter: Computed using the 
               
               
                   
                   
                   
                 RSA-PSS algorithm on the RI Hello 
               
               
                   
                   
                   
                 message up to and excluding the 
               
               
                   
                   
                   
                 Signature parameter, signed by one of 
               
               
                   
                   
                   
                 the RI AIK private keys for which the 
               
               
                   
                   
                   
                 device has pre-acquired the public key. 
               
               
                   
                   
                   
                 Also, make the signature mandatory 
               
               
                   
                   
                   
                 regardless of the success or failure of the 
               
               
                   
                   
                   
                 Device Hello. 
               
               
                   
               
             
          
         
       
     
     Modification to the Registration Request Message and Its Derivation 
     A first modification is to use the device TPM to provide the device nonce. The benefit of this modification is that the TPM provides a secure and reliable pseudo-random number suitable for use for the nonce. 
     A second modification is to include the device TCG credentials in the certificate chain. Including the device TCG credentials can be either in replacement of, or in addition to, the existing OMA DRM 2.0 device credentials. The benefit of including the TCG credentials (such as the EK credential, AIK credentials, platform credential, or the compliance credential) is to add to the trustworthiness of the device. 
     A third modification is to include a list of the TCG CAs trusted by the RI in the trusted RI anchor element. Including the TCG CA&#39;s trusted by the RI can be either in replacement of, or in addition to, the existing OMA DRM 2.0 RI trusted anchor element lists. The benefit of including the list of the TCG CAs trusted by the RI is to add to the trustworthiness of the device. 
     A fourth modification is to include information about the device TPM in the Device Details element of the Extensions parameter. The benefit of including this information is to enhance the trustworthiness about the device to the RI. 
     A fifth modification is to sign the Signature with the device AIK used to sign the modified Device Hello message. The benefit of this modification is to add to the trustworthiness of the device and the Registration Request message due to the highly protected nature of the device AIK. 
     Table 16 shows the format for the modified Registration Request message. 
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 16 
               
             
             
               
                   
               
               
                 Modified Registration Request message format 
               
             
          
           
               
                   
                 Registration 
                 Notes (Changes from the OMA DRM 2.0 
               
               
                 Parameter 
                 Request 
                 ROAP Registration Request message) 
               
               
                   
               
               
                 Session ID 
                 Mandatory 
                 Unchanged. 
               
               
                 Device Nonce 
                 Mandatory 
                 Unchanged in format, but provided by the device TPM. 
               
               
                 Request Time 
                 Mandatory 
                 Unchanged. 
               
               
                 Certificate Chain 
                 Optional 
                 Unchanged in format but listing TCG certificates only, 
               
               
                   
                   
                 or changed in format listing both the OMA DRM certificates and the TCG 
               
               
                   
                   
                 certificates. 
               
               
                 Trusted RI 
                 Optional 
                 Unchanged in format but listing information Authorities 
               
               
                   
                   
                 on TCG CA authorities as RI trust anchors only, or changed in format 
               
               
                   
                   
                 listing both the OMA DRM RI trust anchors and the TCG CA authorities 
               
               
                   
                   
                 as additional RI trust anchors. 
               
               
                 Server Info 
                 Optional 
                 Unchanged. 
               
               
                 Extensions 
                 Optional 
                 All the existing OMA DRM 2.0 Registration Request Extensions 
               
               
                   
                   
                 elements. However, if the device has a TPM then information on device&#39;s TPM 
               
               
                   
                   
                 (such as manufacturer name, version, etc.) should be included in the Device 
               
               
                   
                   
                 Details element. 
               
               
                 Signature 
                 Mandatory 
                 Unchanged in format, but using device TPM&#39;s AIK used in 
               
               
                   
                   
                 signing the modified Device Hello message. 
               
               
                   
               
             
          
         
       
     
     Modification of the Registration Response Message and Its Derivation 
     A first modification is to use the RI TPM to provide a pseudo-random number for the session ID. The benefit of this modification is that the TPM provides a highly secure hardware-based pseudo-random number generator. Using the TPM to generate a pseudo-random number that is used as the session ID strengthens the security of the protocol. 
     A second modification is to use the RI TCG EK credential or the TCG AIK credential belonging to the RI&#39;s TPM to derive the RI ID. The benefit of this modification is that the EK credential and/or the AIK credential is highly protected by the TPM inside the device and deriving the DRM device ID from either of these credentials strengthens the integrity of the DRM device ID information. 
     A third modification is to use the RI TPM to provide the RI nonce. The benefit of this modification is that the RI TPM provides a secure and reliable pseudo-random number suitable for use as the nonce. 
     A fourth modification is to include a list of the TCG CAs trusted by the device in the trusted device anchor element. Including the TCG CAs trusted by the device can be either in replacement of, or in addition to, the existing OMA DRM 2.0 trusted device anchor element lists. The benefit of including the list of the TCG CAs trusted by the device is to add to the trustworthiness of the RI. 
     A fifth modification is to sign the Signature with the RI AIK used to sign the modified RI Hello message. The benefit of this modification is to add to the trustworthiness of the RI and the Registration Response message due to the highly protected nature of the RI AIK. 
     Table 17 shows the format for the modified Registration Response message. 
     
       
         
               
             
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 17 
               
             
             
               
                   
               
               
                 Modified Registration Response message format 
               
             
          
           
               
                   
                 Registration Response 
                   
               
             
          
           
               
                   
                   
                 Status not 
                 Notes (Changes from the OMA DRM 2.0 ROAP 
               
               
                 Parameter 
                 Status = “Success” 
                 “Success” 
                 Registration Response message) 
               
               
                   
               
               
                 Status 
                 Mandatory 
                 Mandatory 
                 Unchanged. 
               
               
                 Session ID 
                 Mandatory 
                 — 
                 Unchanged in format, but use the pseudo- 
               
               
                   
                   
                   
                 random number generated by the RI&#39;s TPM. 
               
               
                 Selected 
                 Mandatory 
                 — 
                 Unchanged. 
               
               
                 Version 
               
               
                 RI ID 
                 Mandatory 
                 — 
                 Unchanged in format, but use the SHA-1 hash 
               
               
                   
                   
                   
                 computed by the RI TPM of either the RI 
               
               
                   
                   
                   
                 TPM&#39;s EK credential or one of the AIK 
               
               
                   
                   
                   
                 credentials. 
               
               
                 Selected Algo. 
                 Mandatory 
                 — 
                 Unchanged. 
               
               
                 RI Nonce 
                 Mandatory 
                 — 
                 Unchanged in format, but use the nonce 
               
               
                   
                   
                   
                 generated by the RI TPM. 
               
               
                 Trusted device 
                 Optional 
                 — 
                 Unchanged in format but listing only the 
               
               
                 Authorities 
                   
                   
                 information on TCG CA authorities that the 
               
               
                   
                   
                   
                 device trusts as the trust anchors, or changed 
               
               
                   
                   
                   
                 in format listing both the OMA DRM device 
               
               
                   
                   
                   
                 trust anchors and the TCG CA authorities 
               
               
                   
                   
                   
                 trusted by the device as additional device trust 
               
               
                   
                   
                   
                 anchors. 
               
               
                 Server Info 
                 Optional 
                 — 
                 Unchanged. 
               
               
                 Extensions 
                 Optional 
                 — 
                 Unchanged. 
               
               
                 Signature 
                 Mandatory 
                 Mandatory 
                 Unchanged in format, but sign with the same 
               
               
                   
                   
                   
                 RI TPM AIK that was used in signing the 
               
               
                   
                   
                   
                 modified RI Hello message. The Signature is 
               
               
                   
                   
                   
                 mandatory regardless of the success or failure 
               
               
                   
                   
                   
                 of the Registration Request message. 
               
               
                   
               
             
          
         
       
     
     Modification of the RO Request Message and Its Derivation 
     A first modification is to use the TPM to create the SHA-1 hash of a selected TCG credential (an EK credential, an AIK credential, a platform credential, or a compliance credential) to use as the device ID. The benefit of this modification is that the credentials are highly protected by the TPM, and thus, deriving the device ID from one of these credentials strengthens the integrity of the device ID information. 
     A second modification is to use the device TPM to generate the device nonce. The benefit of this modification is that a nonce generated by the TPM is secure, due to the TPM&#39;s protected pseudo-random number generation capability. 
     A third modification is to include the device TCG credentials in the certificate chain. Including the TCG credentials can be either in replacement of, or in addition to, the existing OMA DRM 2.0 device credentials. The benefit of including the TCG credentials is to add to the trustworthiness of the device. 
     A fourth modification is to sign the optional DCF Hash with a device AIK in the Extension parameter. The benefit of this modification is that the device AIKs are highly protected, thereby making the DCF signature more secure. 
     A fifth modification is to sign the RO Request message with the device AIK used to sign the most recent successfully responded to Registration Request message. The benefit of this modification is to add to the trustworthiness of the RI and the RO Request message due to the highly protected nature of the RI AIK. 
     Table 18 depicts the format of the modified RO Request message. 
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 18 
               
             
             
               
                   
               
               
                 Modified RO Request message format 
               
             
          
           
               
                   
                 ROAP-RO 
                   
               
               
                   
                 Request 
               
               
                   
                 Mandatory/ 
               
               
                 Parameter 
                 Optional 
                 Notes 
               
               
                   
               
               
                 Device ID 
                 M 
                 Unchanged in format but use the TPM to compute 
               
               
                   
                   
                 the SHA-1 hash of a TCG credential to use as the 
               
               
                   
                   
                 device ID. 
               
               
                 Domain ID 
                 O 
                 Unchanged. 
               
               
                 RI ID 
                 M 
                 Unchanged. 
               
               
                 Device Nonce 
                 M 
                 Unchanged in format but use the nonce generated 
               
               
                   
                   
                 by the device TPM. 
               
               
                 Request Time 
                 M 
                 Unchanged. 
               
               
                 RO Info 
                 M 
                 Unchanged. 
               
               
                 Certificate Chain 
                 O 
                 Use either the device TCG certificate chain or both 
               
               
                   
                   
                 the OMA DRM 2.0 certificate chain plus the device 
               
               
                   
                   
                 TCG certificate chain. 
               
               
                 Extensions 
                 O 
                 Unchanged in format, but when a DCF signature 
               
               
                   
                   
                 is included, sign the DCF with an RI AIK. 
               
               
                 Signature 
                 M 
                 Unchanged in format, but use the TPM to compute 
               
               
                   
                   
                 the signature using the device AIK used to sign 
               
               
                   
                   
                 the most recent successfully responded to 
               
               
                   
                   
                 Registration Request message. 
               
               
                   
               
             
          
         
       
     
     Modification of the RO Response Message and Its Derivation 
     One modification is to use the RI&#39;s TPM to sign the RO Response message with the same RI TPM AIK used in signing the most recent successful Registration Response message. The benefit of this modification is to add to the trustworthiness of the RI and the RO Response message due to the highly protected nature of the RI AIK. 
     Table 19 depicts the format of modified RO Request message. 
     
       
         
               
             
               
               
               
               
             
           
               
                 TABLE 19 
               
             
             
               
                   
               
               
                 Modified RO Response message format 
               
             
          
           
               
                   
                 2-Pass 
                 2-Pass not 
                   
               
               
                 Parameter 
                 Successful 
                 Successful 
                 Notes 
               
               
                   
               
               
                 Status 
                 M 
                 M 
                 Unchanged. 
               
               
                 Device ID 
                 M 
                 — 
                 Unchanged. 
               
               
                 RI ID 
                 M 
                 — 
                 Unchanged. 
               
               
                 Device Nonce 
                 M 
                 — 
                 Unchanged. 
               
               
                 Protected ROs 
                 M 
                 — 
                 Unchanged. 
               
               
                 Cert. Chain 
                 O 
                 — 
                 Unchanged. 
               
               
                 OCSP Response 
                 O 
                 — 
                 Unchanged. 
               
               
                 Extensions 
                 O 
                 — 
                 Unchanged. 
               
               
                 Signature 
                 M 
                 M 
                 Unchanged in format but use the RI TPM 
               
               
                   
                   
                   
                 to sign with the RI AIK used in the most 
               
               
                   
                   
                   
                 recent successful Registration Response 
               
               
                   
                   
                   
                 message. The Signature is mandatory 
               
               
                   
                   
                   
                 regardless of the success or failure of the 
               
               
                   
                   
                   
                 RO Request message. 
               
               
                   
               
             
          
         
       
     
     Although the features and elements of the present invention are described in the preferred embodiments in particular combinations, each feature or element can be used alone (without the other features and elements of the preferred embodiments) or in various combinations with or without other features and elements of the present invention.