ITU-T X.509 PDF

This Recommendation | International Standard addresses some of the security requirements in the areas of authentication and other security services through the provision of a set of frameworks upon which full services can be based. Specifically, this Recommendation | International Standard defines frameworks for:

– public-key certificates;

– attribute certificates; and

– authentication services

The public-key certificate framework defined in this Recommendation | International Standard includes a definition of the information objects for a public-key infrastructure (PKI), including public-key certificates and Certificate Revocation Lists (CRLs). The attribute certificate framework includes a definition of the information objects for a Privilege Management Infrastructure (PMI), including attribute certificates, and Attribute Certificate Revocation Lists (ACRLs). This Recommendation | International Standard also provides the framework for issuing, managing, using and revoking certificates. An extensibility mechanism is included in the defined formats for both certificate types and for all revocation list schemes. This Recommendation | International Standard also includes a set of standard extensions for each, which is expected to be generally useful across a number of applications of PKI and PMI. The schema components (including object classes, attribute types and matching rules) for storing PKI and PMI objects in the Directory, are included in this Recommendation | International Standard. Other elements of PKI and PMI, beyond these frameworks, such as key and certificate management protocols, operational protocols, additional certificate and CRL extensions are expected to be defined by other standards bodies (e.g., ISO TC 68, IETF, etc.).

The authentication scheme defined in this Recommendation | International Standard is generic and may be applied to a variety of applications and environments.

The Directory makes use of public-key certificates and attribute certificates, and the framework for the Directory's use of these facilities is also defined in this Recommendation | International Standard. Public-key technology, including certificates, is used by the Directory to enable strong authentication and signed operations, and for storage of signed data in the Directory. Attribute certificates can be used by the Directory to enable rule-based access control. Although the framework for these is provided in this Recommendation | International Standard, the full definition of the Directory's use of these frameworks, and the associated services provided by the Directory and its components is supplied in the complete set of ITU-T X.500 series of Recommendations | ISO/IEC 9594 (all parts).

This Recommendation | International Standard, in the Authentication services framework, also:

– specifies the form of authentication information held by the Directory;

– describes how authentication information may be obtained from the Directory;

– states the assumptions made about how authentication information is formed and placed in the Directory;

– defines three ways in which applications may use this authentication information to perform authentication and describes how other security services may be supported by authentication.

This Recommendation | International Standard describes two levels of authentication: simple authentication, using a password as a verification of claimed identity; and strong authentication, involving credentials formed using cryptographic techniques. While simple authentication offers some limited protection against unauthorized access, only strong authentication should be used as the basis for providing secure services. It is not intended to establish this as a general framework for authentication, but it can be of general use for applications which consider these techniques adequate.

Authentication (and other security services) can only be provided within the context of a defined security policy. It is a matter for users of an application to define their own security policy which may be constrained by the services provided by a standard.

It is a matter for standards-defining applications which use the authentication framework to specify the protocol exchanges which need to be performed in order to achieve authentication based upon the authentication information obtained from the Directory. The protocol used by applications to obtain credentials from the Directory is the Directory Access Protocol (DAP), specified in Rec. ITU-T X.519 | ISO/IEC 9594-5.