SCDJWS Study Guide: XML Security

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XML Security Overview

XML has become a valuable mechanism for data exchange accross the Internet. Security is essential for the exchange of sensitive XML documents over the public networks. Traditional methods of establishing trust between parties are not appropriate on the public Internet or, indeed, on large LANs or WANs. Security has always been vitally important in the business world to ensure the integrity of content and transactions, to maintain privacy and confidentiality, and to make sure information is used appropriately.

The XML Security standards define XML vocabularies and processing rules in order to meet security requirements. These standards use legacy cryptographic and security technologies, as well as emerging XML technologies, to provide a flexible, extensible and practical solution toward meeting security requirements. The XML Security standards include XML Digital Signature for integrity and signing solutions, XML Encryption for confidentiality, XML Key Management (XKMS) for public key registration, location and validation, Security Assertion Markup Language (SAML) for conveying authentication, authorization and attribute assertions, XML Access Control Markup Language (XACML) for defining access control rules, and Platform for Privacy Preferences (P3P) for defining privacy policies and preferences. Major use cases include securing Web Services (WS-Security) and Digital Rights Management (eXtensible Rights Markup Language 2.0 - XrML).


Security is vital to online business. Technologies designed to meet security requirements have evolved, but the requirements have remained relatively constant. These requirements include Authentication, Authorization, Integrity, Signature, Confidentiality, Privacy and Digital Rights Management and are briefly summarized below:

  • Authentication - Who is it?

    Determine the identity or role of a party attempting to perform some action such as accessing a resource or participating in a transaction. A role may be appropriate to many parties, for example "Human Resources Person".

  • Authorization - What can they do?

    Determine whether some party is allowed to perform a requested action, such as viewing a web page, changing a password, or committing an organization to a 10 million dollar transaction.

  • Integrity - Ensure that information is intact

    Ensure that information is not changed, either due to malicious intent or by accident. This may be information transmitted over a network, such as from a web browser to a web server, information stored in a database or file system, or information passed in a web services message and processed by intermediaries, to give a few examples.

  • Signature - Create and verify electronic signatures analogous to handwritten signatures

    Produce or verify an electronic signature intended to be the equivalent of a handwritten signature. Such a signature may be used for different purposes such as approval, confirmation of receipt, acceptance or agreement.

  • Confidentiality - Make content unreadable by unauthorized parties

    Ensure that content may only be viewed by legitimate parties, even if other access control mechanisms are bypassed. Confidentiality is generally associated with encryption technologies, although other approaches such as steganography (information hiding) might serve a similar purpose.

  • Privacy - Limit access and use of individually identifiable information.

    Personally identifiable information is required by individuals and companies in order to perform services for the individual. An example is a Doctor's office that requires medical records to track a patient's health. Privacy relates to control over what is done with this information and whether it is redistributed to others without the individual's knowledge or consent. Privacy may be managed by a combination of technical and legal means. Confidentiality technology may be used to protect privacy, but cannot prevent inappropriate sharing of information.

  • Digital Rights Management - Limit use and sharing of content according to license agreements

    Ensure that content is used according to license agreements. Generally access rules are incorporated with the content, and enforcement controls are integrated with the clients needed to use the content.

Traditionally, security technologies have required applications to be security or Public Key Infrastructure (PKI) "enabled". This often involves integrating specialized security code with the application in order to meet security requirements. This created a slow, cumbersome and inflexible customization process. An alternative is to create generic XML tools and generic XML Security and then allow them to be used with a variety of XML applications. This allows generic XML Security filters to be applied to arbitrary content without requiring extensive customization for each application, reducing costs and delay.

XML Security

XML Security standards provide a set of technical standards to meet security requirements. These standards are designed to conform to common XML paradigms. The XML Security standards leverage existing XML standards and also enhance XML standards as follows:

  1. The XML Security standards define XML vocabularies for representing security information, using XML technologies, such as XML Schema, for definition. An example is the <KeyInfo> element defined in the XML Digital Signature recommendation for carrying signing or encryption key information. This definition is used in a number of the specifications. The specifications define a shared meaning for the XML vocabularies.
  2. The XML Security standards use other existing XML standards where possible to leverage current XML efforts. For example, XML Digital Signature allows XPath expressions to extract portions of XML for processing..
  3. The XML Security standards are designed to offer the flexibility and extensibility aspects of XML. They allow security to be applied to XML documents, to XML elements and element content, as well as to arbitrary binary documents. They support extending the XML vocabularies through the use of XML namespaces and extensible XML Schema definitions.
  4. XML Security technologies may be applied to end-end security, which is especially important when XML messages are routed through a number of processing intermediaries. Persistent security is associated with the content, rather than with a transport pipe. The security remains with the content. XML Security technologies may be used in conjunction with transport security technologies, such as SSL/TLS, as well.
  5. XML Security technologies reuse existing cryptographic and security technologies whenever possible, without reinventing the wheel. For example, X.509 V3 certificates are used without redefinition when needed - they are simply encoded in a text format. Existing algorithms, such as the SHA1 digest algorithm, are also brought into the XML Security standards world by associating unique URI identifiers with them and defining how they may be used in the XML Security processing models.

The following sections present an overview of the core XML Security standards that are designed to provide XML-compatible technology to meet security requirements. This is followed by some important XML security standards for applying this technology to areas like Web Services and Digital Rights Management.

Core XML Security Standards

The core XML Security standards are:

  1. XML Digital Signature for integrity and signatures,
  2. XML Encryption for confidentiality,
  3. XML Key Management (XKMS) for key management,
  4. Security Assertion Markup Language (SAML) for making authentication and authorization assertions, and
  5. XML Access Control Markup Language (XACML) for stating authorization rules.

The XML Digital Signature recommendation is particularly important; since, as the first XML Security recommendation, it established an approach as well as some vocabulary shared by the other standards. (The <KeyInfo> element defined in the XML Digital Signature recommendation is an element used by other standards, for example.) Signature functionality is also critical for content integrity, so XML Digital Signatures are also incorporated in the other security standards.

Each standard defines the XML vocabulary necessary for describing the security information required for that aspect of security, as well as the processing rules necessary to understand how to apply the standard.

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