Title: TCP EMPLOYMENT ON THE SERVER SIDE

While TCP employment on the user side mainly entails drawbacks for the user, the employment of TCG platforms on the side of a service provider (see ) offers several benefits for both sides. With the employment of TCG platforms on the side of the service provider, users can obtain additional information about its state. Since this technology correctly communicates information about a system and the service user is recipient of additional data there are no drawbacks for him as with the employment on the user/client side and the service user is in a position to make an assessment of the system on the basis of this data. The service provider can use TC platforms to increase the trustworthiness and acceptance of his services. Since a provider, in contrast to a user, appears publicly anyway, it can be assumed that he has no interest in protection against an identification of his platform. Due to this line of interest, the problems and concerns about TCG platforms do not pose any more barriers in this connection.

A user of a service operated on a Trusted Computing platform can receive further information via this extension, provided that the operator of the platform permits it. The accountability of the operator can thereby improve from a user’s viewpoint. 

Figure Usage of a TCG platform on the side of the service provider.

The concept of only executing known code or application code of certain manufacturers or certified code of selected third parties has already been proposed by (Rubin and Geer Jr., 1998).  However it is only possible to communicate an authentication of a remotely running application to an external enquirer in a trustworthy manner through secure coprocessors or TCP approaches. On the basis of this authentication, an enquirer can then determine whether a specific application can be found on a remotely running platform, with which he wishes to communicate. For platforms complying with the Trusted Computing Group specification, the authentication of applications is carried out by way of remote attestation.

illustrates an attestation of a service platform activated by the user of a service and the subsequent evaluation steps by the user. This attestation is fundamental for the approaches presented in this study, since Trusted Computing will be used for assuring the communication of a user with a monitor for enforcing obligations. Provided that a service provider allows the attestation of his systems, a user has the possibility to authenticate this on the basis of the system state and use this as a further criterion for a utilization of services. The service application can thereby already be known to the service user or it has been certified by a trustworthy third party. This requires that a service provider has to fulfil criteria which have to be laid down, e.g. with regard to the confidential processing of personal-related data in order to be listed with a trustworthy third party. The steps of the attestation are as follows:

    1.    Request for an attestation of the platform: The potential user of a service requests the attestation of the service platform before using the service, i.e. the trustworthy verification of the software components and applications implemented there. The service provider prompts the TP module of the service platform to issue the platform configuration and generate its signature.

    2.    Verification of the authenticity of the attestation result: The user receives the attestation information and examines whether its signature has been generated by a valid TPM. For the signature of the platform configuration, the specification 1.1b provides for a classical signature with the RSA algorithm. The specification 1.2 extends the functionality of the TPM by the group signature procedure Direct Anonymous Attestation (DAA) based on zero-knowledge protocols. This type of signature can only be allocated to the group of valid TP modules, but not to an individual module. If the signature is valid, the evaluation of the signed data of the platform configuration can be continued. This step is omitted in the Figure, since no communication between the user and service providers.

In the event that the platform configuration has been signed by an AIK issued by a Privacy CA, this would mean examining whether the certificate pertaining to the signature was issued by a trustworthy entity and whether the certificate still has validity or has been revoked. Conversely, the verification can take place through DAA without contacting a certification authority. The platform configuration is likewise signed by a key pair generated in the TPM. It can be substantiated with the DAA procedure that this key stems from a qualified TP module. 

    3.    Evaluation of the platform configuration: In this step, a mapping is to be made between the platform configuration and the proven attributes of the service application. The desired service application is thereby to be identified in the first step via the platform configuration and in the second step; properties relating to confidentiality or confidential processing are to be learned about. This kind of information can already be locally available on account of former interactions or has to be procured via an independent third entity (trustworthy certifier), with which a trust relationship exists.

    4.    Service access: The user starts the service utilization when both the attestation results have a valid signature generated by a TPM and the information itself identifies an application with known properties with regard to privacy.

Figure Authentication of the application of the service provider through remote attestation.

The advantage of remote attestation is that the service user can authenticate applications on the service platform. This puts the user in a position to verify the presence of a specific service application with a service platform and to enter into communication with it. This can involve applications which have proven attributes with regard to a confidential processing that are confirmed by a certifier or are transparent to the user himself. Through the employment of technology, it is proven that a processing of user data concerning verifiable or certified properties takes place. The trust to be placed in the service provider with regard to the processing of user data can be increased by the use of this technology and provide an additional component for the formation of trust. 

The transfer from an authentication (of identities) of a service provider to the authentication of his application therefore presents a further decision criterion for the service user when selecting services.