Security for Virtual Organizations: Federating Trust and Policy Domains

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Excerpt from chapter 21 of Grid 2: Blueprint for a New Computing Infrastructure.

21.1.3 Security Challenges and Requirements

Security requirements within the Grid environment are driven by the need to support scalable, dynamic, distributed virtual organizations (281) (VOs, Chapter 4)— collections of diverse and distributed individuals and organizations that seek to share and use diverse resources in a coordinated fashion. The VO concept serves as the basis for the Grid security model that we introduce to support scenarios such as that in Section 21.1.2: Resources from multiple locations are coordinated to serve an even larger, more distributed collection of users.

From a security perspective, a key attribute of VOs is that, in addition to VO-specific policy, participants and resources are governed by the rules and policies of the classical organizations of which they are members. Furthermore, whereas some VOs, such as the multiyear scientific collaboration given in the example, will be large and long-lived (in which case explicit negotiations with resource providers are acceptable), others will be short-lived—created, perhaps, to support a single task, such as two individuals sharing documents and data as they write a proposal—in which case overheads associated with VO creation and operation must be minimal.

A fundamental requirement is thus to enable access by VO members to resources that live within classical organizations and that, from the perspective of those classical organizations, have policies in place that speak only about local users. This VO access must be established and coordinated only through binary trust relationships that exist between the local user and their organization and between the VO and the user. We cannot, in general, assume trust relationships between the classical organization and the VO or its external members.

Grid security mechanisms can address these challenges by allowing a VO to be treated as a policy domain overlay (see Figure 21.2). Multiple resources or organizations outsource certain policy control(s) to a third party, the VO, which coordinates the outsourced policy in a consistent manner to allow for coordinated resource sharing and use.

Figure 21.2: A virtual organization policy domain overlay pulls together participants and resources from disparate domains into a common trust domain.

Complicating Grid security is the fact that new services (i.e., resources) may be deployed and instantiated dynamically over a VO’s lifetime. For example, a user may establish personal stateful interfaces to existing resources, or the VO itself may create directory services to keep track of VO participants. Like their static counterparts, these resources must be securely coordinated and must interact with other services.

This combination of dynamic policy overlays and dynamically created entities drives the need for three key characteristics in a Grid security model:

• Enables integration and interoperability. Organizations participating in a VO often have significant investment in existing security mechanisms and infrastructure. Grid security, rather than replacing these mechanisms, must enable integration and interoperability between them.

• Enables creation and management of dynamic trust domains. Not only must parties in a VO be able to interoperate at the level of protocols, but in order to coordinate resources, VOs need to establish trust among VO users and resources. These trust domains can span multiple organizations and must adapt dynamically as participants join or leave the VO.

• Supports dynamic creation of services. Users must be able to create new services (e.g., “resources”) dynamically without administrator intervention. These services need to be coordinated and must interact securely with other services.

Thus, we must be able to name the service with an assertable identity and grant access rights to that identity without contradicting the governing local policy.

Traditional means of security administration that involve manual editing of centralized policy databases or issuance of credentials through elaborate procedures cannot meet the demands of these dynamic scenarios. We require a user-driven security model that allows users to create entities and policy domains in order to create and coordinate resources within VOs.

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