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This part of ISO/IEC 9594:
- 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 part of ISO/IEC 9594 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 t o 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 ISO/IEC 9594-5.
The strong authentication method specified in this part of ISO/IEC 9594 is based upon public-key cryptosystems. It is a major advantage of such systems that user certificates may be held within the Directory as attributes, and may be freely communicated within the Directory System and obtained by users of the Directory in the same manner as other Directory information. The user certificates are assumed to be formed by 'off-line' means, and placed in the Directory by their creator. The generation of user certificates is performed by some off- line Certification Authority which is completely separate from the DSAs in the Directory. In particular, no special requirements are placed upon Directory providers to store or communicate user certificates in a secure manner.
A brief introduction to public-key cryptography can be found in annex B.
In general, the authentication framework is not dependent on the use of a particular cryptographic algorithm, provided it has the properties described in 6.1. Potentially a number of different algorithms may be used. However, two users wishing to authenticate shall support the same cryptographic algorithm for authentication to be performed correctly. Thus, within the context of a set of related applications, the choice of a single algorithm will serve to maximize the community of users able to authenticate and communicate securely. One example of a public key cryptographic algorithm can be found in Annex C.
Similarly, two users wishing to authenticate shall support the same hash function (see 3.3f) (used in forming credentials and authentication tokens). Again, in principle, a number of alternative hash functions could be used, at the cost of narrowing t he communities of users able to authenticate. A brief introduction to hash functions together with one example hash function can be found in annex D.