1. XACML and the Cloud

2. What is XACML? XML language for access control Coarse or fine-grained
Extremely powerful evaluation logic
Ability to use any available information
Superset of Permissions, ACLs, RBAC, etc
Scales from PDA to Internet
Federated policy administration
OASIS and ITU-T Standard
XACML specifies an abstract access control policy language and rules for evaluating policies, an XML format for exchanging policies and an optional XML format for decision inputs and outputs.
Information provided may be included in complex logical expressions to produce evaluatable policies corresponding to real world policy requirements.
XACML provides all the functionality of familiar Access Control models, while enabling capabilities far beyond them.
XACML was designed to operate in many different software and hardware environments, operating at a range of scales.
XACML enables multiple administrators to create policies with overlapping scopes without close cooperation. Decision conflicts are resolved by combining rules.
XACML 2.0 is an OASIS Standard and ITU-T Recommendation X.1142.
XACML 3.0 has reached the level of OASIS Committee Specification and is expected to become as OASIS Standard and ITU-T Recommendation.

3. XACML Cloud Features Powerful language features
Capture complex business relationships
Federated Administration
Combining algorithms resolve conflicts
Administrative Policies
Policies managed by providers, customers, end users
Global identifiers prevent name conflicts
Domain-specific Profiles
Healthcare, Intellectual property, Privacy
XACML has many built-in features which meet important Cloud Computing requirements.
The language, with its ability to combine virtually any available data in arbitrarily complex logical expressions is well suited to expressing the complex rules needed in multi-party service environments which characterize the Cloud..
Administrators working for cloud providers, their customers and end users may all potentially manage policies which cover the same sets of users or resources without the need for close coordination. Decision conflicts at runtime will be resolved by combining algorithms.
XACML 3.0 provides the capability to create Administrative Policies which enable individuals to create policies within a specified scope. For example, a cloud provider can permit its customers to create policies covering their own services or users. Administrative Policies can be nested, allowing further access to be delegated in a controlled way.
XACML identifiers are all set in a global namespace (urn:oasis:names:tc:xacml:…) thus avoiding conflicts.
The core XACML specifications cover Access Control in general. The TC has also specified identifiers which are applicable to specific domains of use for example the XSPA profile which covers Healthcare and the Intellectual Property Control Profile and the Privacy profile.

4. XACML Enables Efficient Cloud Implementations
Stateless Server
Choice of imbedded or server-based PDP
Max performance or Access Control Service
Specification permits optimizations
Order of evaluation
Caching of Attributes
Caching of decisions or partial evaluations
The XACML Specifications have been written with the goal of enabling implementations to be highly efficient and scalable. These are some examples of this.
The XACML PDP is operates in a stateless mode, which reduces the resources it needs to consume and greatly simplifies error recovery. The overall effect is to enable scalability.
An XACML Policy Decision Point (decision engine) may be imbedded in the same process as the Policy Enforcement Point for minimum overhead and maximum performance. Alternatively, the PDP may be implemented as an Authorization server which is accessed remotely. This greatly simplifies integration into existing applications and also permits Authorization to be offered as a Cloud service.
The XACML Specifications provide as much implementation flexibility as possible, while retaining the principle that given the same policies and the same input attributes, all compliant XACML PDPs should produce the same decision.
This flexibility allows XACML implementations to perform optimizations which further enhance scalability. For example, an XACML-compliant PDP can evaluate policy expressions in any order it chooses or even distribute the evaluation over multiple processors or systems. An XACML PDP can cache Attribute values for use in future decisions. A PDP can also cache complete Policy decisions or even results of expressions within policies for use in future requests or within a multiple decision request.