Webservice Security Standards

SOA adoption is on the rise and Webservices is predominantly used for its implementation. Webservice messages are sent across the network in an XML format defined by the W3C SOAP specification. Webservices have come a long way and has sufficiently matured to offer the required tenets especially on the security domain. In this blog let us have a quick look at the available standards with respect to the security dimensions and look at how the related security requirements are addressed.

Secure Messaging

• WS-Security - This specification was originally developed by IBM, Microsoft and Verisgn and OASIS (Organization for the Advancement of Structured Information Standards) continued the work on this standard. This standard addresses the Integrity and Confidentiality requirements of the webservice messages. The specification describes the signing, encrypting of the SOAP messages and also about attaching security tokens. Various signature formats and encryption algorithms are supported. The security tokens supported include: X.509 Certificates, Kerberos tickets, User ID/Password credentials, SAML assertions and custom tokens. Due to the increased size of the SOAP messages and the cryptographic requirements, this standard requires significantly higher compute resources and network bandwidth.
• SSL/TLS - SSL was developed by Netscape Communications Corporation in 1994 to secure transactions over the World Wide Web. Soon after, the Internet Engineering Task Force (IETF) began work to develop a standard protocol that provided the same functionality. They used SSL 3.0 as the basis for that work, which became the TLS protocol. In applications design, TLS is usually implemented on top of any of the Transport Layer protocols, encapsulating the application-specific protocols such as HTTP, FTP, SMTP, NNTP and XMPP. Historically it has been used primarily with reliable transport protocols such as the Transmission Control Protocol (TCP). This standard helps address the Strong authentication, message privacy and integrity requirements.

Resource Protection

• XACML - eXtensible Access Control Markup Language defines a declarative access control policy language implemented in XML and a processing model describing how to evaluate access requests. Version 3.0 of this standard has been published by OASIS in January 2013. The new features of the latest version of this standard include: Multiple Decision Profile, Delegation, Obligation Expressions, Advice Expressions and Policy Combination Algorithms.While there are many ways the base language can be extended, many environments will not need to do so. The standard language already supports a wide variety of data types, functions, and rules about combining the results of different policies. In addition to this, there are already standards groups working on extensions and profiles that will hook XACML into other standards like SAML and LDAP, which will increase the number of ways that XACML can be used.
• XrML - Developed by Content Guard, a subsidiary of Xerox, and supported by Microsoft, eXtensible Rights Markup Language would provide a universal method for specifying rights and issuing conditions associated with the use and protection of content in a digital rights management system. XrML licenses can be attached to WS-Security in the form of tokens. XACML and XrML both deal with authorization. They share requirements from many of the same application domains. Both share the same concepts but use different terms. Both are based on XML Schema. Microsoft's Active Directory Rights Management Services (AD RMS) uses the eXtensible rights Markup Language (XrML) in licenses, certificates, and templates to identify digital content and the rights and conditions that govern use of that content.
• RBAC, ABAC - Similar to XrML, RBAC and ABAC are established approaches to define and implement Role Based Access Control and Attribute Based Access Controls and can be attached to WS-Security as tokens. The use of RBAC or ABAC to manage user privileges (computer permissions) within a single system or application is widely accepted as a best practice.
• EPAL - The Enterprise Privacy Authorization Language (EPAL) is an interoperability language for exchanging privacy policy in a structured format between applications and can be leveraged for addressing the privacy concerns with the SOAP messages. An EPAL policy categorizes the data an enterprise holds and the rules which govern the usage of data of each category. Since EPAL is designed to capture privacy policies in many areas of responsibility, the language cannot predefine the elements of a privacy policy. Therefore, EPAL provides a mechanism for defining the elements which are used to build the policy.

Negotiation of Contracts

• ebXML - e-business XML is a modular suite of standards advanced by OASIS and UNCEFACT and approved as ISO 15000. While the ebXML standards seek to provide formal XML-enabled mechanisms that can be implemented directly, the ebXML architecture is focused on concepts and methodologies that can be more broadly applied to allow practitioners to better implement e-business solutions. ebXML provides companies with a standard method to exchange business messages, conduct trading relationships, communicate data in common terms and define and register business processes. A CPA (Collaboration Protocol Agreement) document is the intersection of two CPP documents, and describes the formal relationship between two parties.
• SWSA - The SWSA(Semantic Web Services Architecture) interoperability architecture covers the support functions to be accomplished by Semantic Web agents (service providers, requestors, and middle agents). While not all operational environments will find it necessary to support all functions to the same degree, the distributed functions to be addressed by this architecture to include: Dynamic Service Discovery, Service Engagement (Negotiating & Contracting), Service Process Enactment & Management, Semantic Web Community Support Services, Semantic Web Service Lifecycle & Resource Management Services and Cross Cutting Issues.

Trust Management

• WS-Trust - The goal of WS-Trust is to enable applications to construct trusted SOAP message exchanges. This trust is represented through the exchange and brokering of security tokens. This specification provides a protocol agnostic way to issue, renew, and validate these security tokens. The Web service security model defined in WS-Trust is based on a process in which a Web service can require that an incoming message prove a set of claims (e.g., name, key, permission, capability, etc.). If a message arrives without having the required proof of claims, the service SHOULD ignore or reject the message. A service can indicate its required claims and related information in its policy as described by WS-Policy and WS-PolicyAttachment specifications.
• XKMS - XML Key Management Specification is a protocol developed by W3C which describes the distribution and registration of public keys. Services can access an XKMS compliant server in order to receive updated key information for encryption and authentication. The XML Key Management Specification (XKMS) allows for easy management of the security infrastructure, while the Security Assertion Markup Language (SAML) makes trust portable. SAML provides a mechanism for transferring assertions about authentication of entities between various cooperating entities without forcing them to lose ownership of the information.
• SAML - Security Assertion Markup Language is a product of the OASIS Security Services Technical Committee intended for exchanging authentication and authorization data between parties, in particular, between an identity provider and a service provider. SAML allows business entities to make assertions regarding the identity, attributes, and entitlements of a subject (an entity that is often a human user) to other entities, such as a partner company or another enterprise application. SAML specifies three components: assertions, protocol, and binding. There are three assertions: authentication, attribute, and authorization. Authentication assertion validates the user's identity. Attribute assertion contains specific information about the user. And authorization assertion identifies what the user is authorized to do. Protocol defines how SAML asks for and receives assertions. Binding defines how SAML message exchanges are mapped to Simple Object Access Protocol (SOAP) exchanges.
• WS-Federation - WS-Federation extends the WS-Security, WS-Trust and WS-SecurityPolicy by describing how the claim transformation model inherent in security token exchanges can enable richer trust relationships and advanced federation of services. A fundamental goal of WS-Federation is to simplify the development of federated services through cross-realm communication and management of Federation Services by re-using the WS-Trust Security Token Service model and protocol. A variety of Federation Services (e.g. Authentication, Authorization, Attribute and Pseudonym Services) can be developed as variations of the base Security Token Service. 

Security properties

• WS-Policy, WS-SecurityPolicy - WS-Policy represents a set of specifications that describe the capabilities and constraints of the security policies on intermediaries and end points and how to associate policies with services and end points. Web Services Policy is a machine-readable language for representing these Web service capabilities and requirements as policies. Policy makes it possible for providers to represent such capabilities and requirements in a machine-readable form. A policy-aware client uses a policy to determine whether one of these policy alternatives (i.e. the conditions for an interaction) can be met in order to interact with the associated Web Service. Such clients may choose any of these policy alternatives and must choose exactly one of them for a successful Web service interaction. Clients may choose a different policy alternative for a subsequent interaction.
• WS-ReliableMessaging, WS-Reliability - WS-ReliableMessaging, was originally written by BEA Systems, Microsoft, IBM, and Tibco and later submitted to the OASIS Web Services Reliable Exchange (WS-RX) Technical Committee for adoption and approval.Prior to WS-ReliableMessaging, OASIS produced a competing standard WS-Reliability that was supported by a coalition of vendors. The protocol allows endpoints to meet the guarantee for the delivery assurances namely, Atmost Once, Atleast Once, Exactly Once and In Order. Persistence considerations related to an endpoint's ability to satisfy the delivery assurances are the responsibility of the implementation and do not affect the wire protocol.