    Network Working Group                                S. Hardcastle-Kille
    Request for Comments: 1430                              ISODE-Consortium
                                                                   E. Huizer
                                                                  SURFnet bv
                                                                     V. Cerf
                               Corporation for National Research Initiatives
                                                                    R. Hobby
                                             University of California, Davis
                                                                     S. Kent
                                                    Bolt, Beranek and Newman
                                                               February 1993

                       A Strategic Plan for Deploying an
                        Internet X.500 Directory Service

    Status of this Memo

       This memo provides information for the Internet community.  It does
       not specify an Internet standard.  Distribution of this memo is
       unlimited.

    Abstract

       There are a number of reasons why a new Internet Directory Service is
       required.  This document describes an overall strategy for deploying
       a Directory Service on the Internet, based on the OSI X.500 Directory
       Service.  It then describes in more detail the initial steps which
       need to be taken in order to achieve these goals, and how work
       already undertaken by Internet Engineering Task Force Working Groups
       (IETF WGs) is working towards these goals.

    Table of Contents

       1.    REQUIREMENTS                                                  2
       2.    SUMMARY OF SOLUTION                                           3
       3.    INFORMATION FRAMEWORK                                         3
       3.1   The Technical Model                                           3
       3.2   Extending the Technical Model                                 4
       3.3   The Operational Model                                         5
       4.    NAME ASSIGNMENT                                               5
       5.    DIRECTORY INFRASTRUCTURE                                      6
       5.1   Short Term Requirements                                       7
       5.2   Medium Term Requirements                                      9
       5.3   Long Term Requirements                                        9
       6.    DATAMANAGEMENT                                                9
       6.1   Legal Issues                                                 10
       7.    TECHNICAL ISSUES                                             10

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       7.1   Schema                                                       11
       7.2   Use on the Internet                                          11
       7.3   Replication of Knowledge and Data                            12
       7.4   Presentation of Directory Names                              13
       7.5   DSA Naming and MD Structure                                  13
       8.    SECURITY                                                     13
       8.1   Directory Provision of Authentication                        14
       8.2   Directory Security                                           15
       9.    RELATION TO DNS                                              16
       10.   EXTERNAL CONNECTIONS                                         16
       11.   REFERENCES                                                   17
       12.   Security Considerations                                      19
       13.   Authors' Addresses                                           20

    1.  REQUIREMENTS

       There is substantial interest in establishing a new Directory Service
       on the Internet. In the short term, there is pressure to establish
       two new services:

       -  White Pages lookup of users;

       -  Support for X.509 Authentication for a range of applications in
          particular for Privacy Enhanced mail [Lin89].

       In the medium term, there are likely to be many requirements for
       Directory Services, including:

       - General resource lookup, for information ranging from committee
         structures to bibliographic data;

       - Support of management of the Internet infrastructure, and
         integration of configuration information into the higher level
         directory;

       - Support of applications on the Internet. For example:

          o  Electronic distribution lists;
          o  Capability information on advanced user agents;
          o  Location of files and archive services.

       - Support for Mail Handling Systems; Be they RFC-822 based or X.400
         based (IETF MHS-DS WG), e.g.,:

          o  Support for routing;
          o  Info on User agent capabilities; essential for a usage of
             Multimedia mail like MIME (Multipurpose Internet Mail
             Extensions).

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       For the longer term, more sophisticated usages of X.500 are possible
       extending it into a useful and fast yellow pages service.

    2. SUMMARY OF SOLUTION

       In principle, the current Internet Domain Name System (DNS) could be
       used for many of these functions, with appropriate extensions.
       However, it is suggested that a higher level of directory service is
       needed. It is proposed to establish an Internet Directory Service
       based on X.500.  This provides appropriate functionality for the
       services envisaged and gives flexibility for future extension. This
       extension could be achieved either by tracking the evolution of the
       OSI Standard or by work specific to the Internet. In practice, it is
       likely to be a mixture of both.

       By deploying X.500 in some form on the Internet, a truly global and
       universal Directory Service can be built that will provide Internet
       users with fast access to all kinds of data. The X.500 Directory
       Service in this case may range from a simple white pages service
       (information on people and services) to coupling various existing
       databases and information repositories in a universal way.

       Currently, several different but cooperating X.500 Directory Services
       pilots are taking place on the Internet. These pilots form an
       important base for experimenting with this new service. Starting with
       these pilots, with the X.500 products arriving on the market today,
       and given sufficient funding for the central services described in
       this paper an operational X.500 Directory Service can be deployed.

       The final goal of the strategy described in this paper is to deploy a
       fully operational Directory Service on the Internet, providing the
       functions mentioned in the previous section.

    3.  INFORMATION FRAMEWORK

       The most critical aspect of the Directory Service is to establish an
       Internet Information Framework. When establishing a sophisticated
       distributed directory with a coherent information framework, it
       involves substantial effort to map data onto this framework. This
       effort is an operational effort and far outweighs the technical
       effort of establishing servers and user agents.

    3.1   The Technical Model

       By choosing the X.500 model as a basis for the information framework,
       it will also be part of a (future) global information framework. The
       key aspects of this model are:

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       - A hierarchical navigational system that couples distributed
         databases (of various kinds), which allows for management of the
         data by the organization/person responsible for the data;

       - Each object in this information structure (called the Directory
         Information Tree, DIT) is represented as an entry;

       - Objects are typed by an "object class", which permits multiple
         inheritance;

       - An object is described by a set of attributes;

       - Each attribute is typed. Attribute types are hierarchical;

       - Each attribute type has an associated attribute syntax, which may
         be generic or shared with other attributes (e.g., Integer Syntax;
         Distinguished name Syntax); This allows for representation of
         simple attributes (e.g., strings or bitmaps) or complex ones with
         detailed structures.

       - Each entry has an unambiguous and unique global name;

       - Alternate hierarchies may be built by use of aliases or pointers of
         distinguished name syntax.

       This framework allows for representation of basic objects such as
       users within organizations. It is also highly extensible, and so can
       be used for a range of other applications.

    3.2   Extending the Technical Model

       In the longer term, the model could be extended to deal with a number
       of other requirements which potentially must be met by an Internet
       Directory Service. Possible extensions include:

       - Support of ordered attributes (needed by some applications such as
         message storage);

       - Extensions to allow unification with management information,
         associated with SNMP (Simple Network Management Protocol) [CFSD90]
         or other management protocols;

       - Handling of non-hierarchical data in a better manner for searching
         and retrieval, whilst retaining the basic hierarchy for management
         purposes.  This is essentially building a general purpose resource
         location service on top of the basic infrastructure. It will need
         work on the information model, and not just the access protocols.

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       It is noted that although X.500 may not provide the ultimate solution
       to information retrieval, it has good potential for solving a lot of
       information service related problems.

    3.3   The Operational Model

       To make the Directory Service with a coherent information framework
       really operational requires a lot of effort. The most probable
       operational model is one where larger organizations on the Internet
       maintain their part of the DIT on their own DSA (Directory System
       Agent). Smaller organizations will "rent" DSA space from regional
       networks or other service providers. Together these DSAs will form
       the Internet Directory Service Infrastructure. To couple the various
       parts of the DIT that are contained on these Internet DSAs, a special
       DSA containing the Root for the naming hierarchy within the DIT has
       to be established and maintained.

       The following tasks can be foreseen:

       -  Defining the naming hierarchy; See section 4.
       -  Creating the Directory Infrastructure; See section 5.
       -  Getting the Data into the directory; and
       -  Managing the data in the Directory. See section 6.

    4.  NAME ASSIGNMENT

       In order to deploy the Internet Directory Service, it is important to
       define how the naming hierarchy will be structured. Although the
       basic model suggests a simple monolithic "database" containing all of
       the Internet's information infrastructure, with a namespace divided
       along geographic boundaries, this may not be the definite model that
       turns out to be the most appropriate to the Internet. Different
       models may evolve according to the needs of the Internet and the
       applications used on the Internet (i.e., some parts of the DIT may be
       assigned at the root for the Internet). Below this one can envisage
       several loosely coupled namespaces each with their own area of
       applicability. This should be handled as a part of the general
       operation of a directory service. An example of this might be
       assignment of a representation of the Domain Namespace under the root
       of the DIT. This is further discussed in [BHK91a].

       However, the core DIT information will be nationally assigned. The
       parts of the DIT below country level will be managed differently in
       each country. In many countries, registration authorities will be
       established according to the OSI Standard [ISO]. This has been done
       in some countries by the national ISO member body representative (for
       example in the UK by BSI).

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       The lower parts of the hierarchy will, in general, be delegated to
       organizations who will have control over Name Assignment in that part
       of the tree. There is no reason to mandate how to assign this
       hierarchy, although it is appropriate to give guidelines. Proposed
       solutions to assignment of namespace are given in [BHK92].

       In North America, there is an alternative approach being developed by
       the North American Directory Forum (NADF), which leverages existing
       registration mechanisms [For91]. It is not yet clear what form a
       final North American Directory Service will take. It is expected that
       similar initiatives will be taken in other places, such as Europe.
       For the Internet, the Internet Society (ISOC) has been suggested as a
       possible Naming Authority.

       A discussion of the main issues involved with representing the Real
       World in the Directory Service is part of the work undertaken by the
       IETF OSI DS Working Group.

       The core of the Internet Directory will therefore come to exist of a
       country based structure with different national naming schemes below
       the countries.  It is clearly desirable that the Internet Directory
       Service follows any evolving national and international hierarchies.
       However, this should not be allowed to cause undue delay. The
       strategy proposed is to proceed with name assignment as needed, and
       to establish interim registration authorities where necessary, taking
       practical steps to be aligned with emerging national authorities
       wherever possible.

       It is suggested that the Internet Directory Service does two things:

       First, each national part of the Internet DIT namespace should be
       delegated to an appropriate organization, which will usually be in
       the country of question.  Second, the delegated organization should
       assign names for that country as part of the Internet Directory
       Service. This should be done in a manner which is appropriately
       aligned with any emerging local or national service, but does not
       unduly delay the deployment of the Internet Directory Service.  For
       most countries, this will fit in as a natural evolution of the early
       directory piloting, where operators of pilots have acted as interim
       name registration authorities.

    5.  DIRECTORY INFRASTRUCTURE

       To provide access to the Internet Directory Service, an
       infrastructure has to be built. Although the technical components of
       an X.500 infrastructure are clear: DSAs (that hold the actual data)
       and DUAs (that allow users and applications to access the data), a
       lot more is needed for deployment of an Internet Directory Service.

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    RFC 1430                     X.500 Strategy                February 1993

       The Integrated Directory Services (IDS) Working Group of the IETF is
       playing a key role in solving most of the issues that are related to
       the building of an appropriate infrastructure.

       Many of the issues cited in this section have come forward out of
       interim pilots that have been established on the Internet:

       PSI White Pages Pilot
          This is a pilot service which is operating X.500 on the Internet.
          In many ways it is operating as an Internet wide pilot.

       FOX
          Fielding Operational X.500, a project to explore the development
          and interoperability of X.500 implementations.

       Paradise (Piloting A ReseArch DIrectory Service in Europe)
          This project has been providing the necessary glue to hold the
          various national activities together [Par91].

    5.1   Short Term Requirements

       -  Central Operations. There is a need for a number of operations
          to be managed as a service for the whole Internet. These services
          are:

          o A root DSA; containing the top-level of the DIT, has to be
            provided.  Currently, this root DSA is managed by the Paradise
            project.

          o Name assignment; Inserting names into the Directory, this has
            been discussed in section 4. This could be done in conjunction
            with the appropriate Registration Authority or by the
            Registration Authority.  In most cases it is likely to be the
            former, and mechanisms will need to be set up to allow
            organizations to get their names installed into the directory,
            either direct or through the registration authority.

          o Knowledge management; i.e., the information on "which DSA holds
            what part of the DIT, and how can that DSA be accessed". DSAs
            will be established by Organizations. There will be a need to
            centrally coordinate the management of the knowledge information
            associated with these DSAs. This is likely to be coupled to the
            name assignment.

          o Knowledge and Data replication; For the Directory to perform
            well, knowledge and data high up in the DIT must be
            significantly replicated. A service must be provided to make
            replicated information available to DSAs that need it.

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          It is suggested that for the time being, Paradise should be used
          as the initial basis for handling the top-level of the DIT and for
          provision of the central services. However, the services mentioned
          above need to be provided at a national level for every
          participating country in the Internet Directory Service. Whenever
          an organization starts a new country branch of the DIT in the
          Internet Directory Service the central operations will have to
          help out to make sure that these services will be properly
          installed on a national level.

       - An effective service will need to have sufficient implementations,
         in order to give full coverage over different hardware and software
         platforms, and to demonstrate openness. The recent Directory
         Information Services (pilot) Infrastructure Working Group's (DISI)
         Survey of Directory Implementations suggests that there will not be
         a problem here.  This provides a list of available X.500
         implementations and their capabilities [LW91].

       - An executive summary, necessary to convince the management of
         computer centers to invest manpower into setting up a X.500
         Directory Service.  This is provided by DISI [WR92].

       - Due to the possible different and rather independent structured
         namespaces that can be envisaged in the DIT for different purposes,
         DUAs will have to be "tuned intelligently" for the applications that
         they are used for.

       - To allow users easy access to the Internet Directory Service even
         from low powered workstations, a lightweight protocol has to be
         developed over TCP/IP. Already two private protocols that do this
         have been developed: The Michigan DIXIE protocol [HSB91] and the PSI
         Directory Assistance Service [Ros91]. The IETF OSI Directory
         Services Working Group (OSI-DS WG) is currently working on a
         standard lightweight protocol called LDAP.

       - Although the Internet Directory Service does not have to make any
         mandatory requirements about the use of lower layers, it is noted
         that the use of STD 35, RFC 1006 to allow use of OSI applications on
         top of TCP/IP is essential for deployment in the Internet. Other
         stacks like the ones using CLNS, CONS and X.25(80) will probably
         also be deployed in parts of the Internet. DSAs with different
         stacks will be linked through use of either application level relays
         (chaining) or Transport Service bridges.

       - There are multiple issues that are not dealt with (properly) in the
         X.500 standard and thus prevent the building of an Internet
         Directory service.  Intermediate solutions for these issues have to
         be established in an "open" way. The results will have to be

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         deployed as well as to be fed back into the relevant standard
         committees. The IETF OSI-DS WG deals with these issues. Section 7
         describes several of these issues.

       - Site support. The IETF IDS WG is looking at providing the necessary
         documentation to help with the provision of support for Directory
         users at participating sites.

    5.2   Medium Term Requirements

       - Enhanced performance is necessary to allow for a real global usage;

       - The schema has to be extended to allow for various kinds of data,
         e.g.,:

          o  NIC data;
          o  Resource location;

       - Support for Internet Message Handling services (RFC-822, MIME and
         X.400).  This work is already undertaken by the IETF MHS-DS WG.

    5.3   Long Term Requirements

       - To make sure that X.500 evolves into an operational service, it is
         essential to track its evolution, and to feed back into the
         evolution process.

       - Interface existing RDBMS into the Directory Service.

       - To increase the performance of the directory, and thereby making it
         useful for an even wider range of applications (e.g., policy based
         routing), a lightweight protocol for access and system usage is
         needed.

    6.  DATAMANAGEMENT

       The whole of the Directory Infrastructure won't stand much chance
       without proper datamanagement of the data contained within the DIT.
       Procedures need to be established to assure a certain Level of
       Quality of the data contained in the DIT.

       Due to the very nature of X.500, the management of the data is
       distributed over various sources. This has the obvious advantage that
       the data will be maintained by the owner of the data. It does
       however, make it quite impossible to describe one single procedure
       for datamanagement.

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       For the Internet Directory Service, guidelines will have to be
       developed (by the IETF IDS WG), to help organizations that start with
       deployment of X.500 on how to manage data in their part of the DIT.
       The guidelines should describe a minimum level of quality that has to
       be supplied to make the service operational. The IETF OSI-DS WG will
       initiate a pilot on Quality of Service parameters in the Directory,
       that will be of use.

       Pilot datamanagement projects will have to be done (e.g., existing
       databases should be connected to the Internet Directory Service).
       Tools that are developed to achieve this should be made available to
       the Internet community for possible future use.

    6.1   Legal Issues

       Most countries connected to the Internet have some sort of law that
       dictates how data on people can and cannot be made available. These
       laws deal with privacy and registration issues, and will differ from
       country to country.  It is suggested that each of the national
       organizations within the Internet that manages the Internet Directory
       Services master for that country, undertake some research as to the
       applicability of laws within that country on data made public through
       use of X.500.

       In the mean time, a general "User Bill of Rights" should be
       established to indicate what the proper use of the Internet Directory
       Service is. This "Bill of Rights" could be drafted by the IETF IDS
       WG.  As a basis, the NADF "User Bill of Rights" [For92] can be used.

    7.  TECHNICAL ISSUES

       The IETF has established the OSI-DS WG. The major component of the
       initial work of this group is to establish a technical framework for
       deploying a Directory Service on the Internet, making use of the
       X.500 protocols and services [CCI88b].  This section describes the
       work already done by this working group, which has been implicitly
       focused on the technical infrastructure needed to deploy the Internet
       Directory service.

       The OSI Directory Standards do not yet contain sufficient specifics
       to enable the Internet Directory Service to be built. Full openness
       and interoperability are a key goal, so we may need Internet specific
       agreements, at least until the ISO standards are more complete. This
       section notes areas where the standards do not have sufficient
       coverage, and indicates the RFCs which have been written to overcome
       these problems.

       The work is being limited to (reasonably well) understood issues.

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       This means that whilst we will attempt to solve a wider range of
       problems, not all potential requirements will necessarily be met.

       The technical work is done in conjunction with the RARE WG on Network
       Application Support WG (formerly RARE WG3). The IETF WGs and the RARE
       WG have a common technical mailing list. It is intended that this
       will lead to a common European and North American technical approach.

    7.1   Schema

       A Directory needs to be used in the context of an Information
       Framework. The standard directory provides a number of a attributes
       and object classes to enable basic operation. It is certain that the
       Internet community will have requirements for additional attributes
       and object classes. There is a need to establish a mechanism to
       register such information.

       Pilots in the European RARE Community and the US PSI White Pages
       Pilot have based their information framework on the THORN and RARE
       Naming Architecture. This architecture should be used for the
       Internet Directory Service, in conjunction with COSINE based services
       in Europe. A revised version of the Naming Architecture, with a
       mechanism for registration of new attributes and object classes, has
       been released as RFC 1274 [BHK91a].

    7.2   Use on the Internet

       It is a recognized policy on the Internet to deploy OSI Applications
       over non-OSI lower layers (such as STD 35, RFC 1006) [RC87]. This
       policy allows deployment of OSI Applications before an OSI lower
       layer infrastructure has been deployed. Thus, the Internet Directory
       Service will decouple deployment of the OSI Directory from deployment
       of the OSI lower layers. As the Internet Directory service will
       extend into the far corners of the Internet namespace, where the
       underlying technology is not always TCP/IP, the Internet Directory
       Service will not make any mandatory requirements about use of lower
       layers. When configuring the Internet Directory Services, variations
       in the lower layers must be considered. The following options are
       possible:

       - Operation on top of TCP/IP using a lightweight protocol.

       - Operation over TCP/IP using STD 35, RFC 1006. This is a practical
         requirement of deployment at very many Internet sites, and is the
         basis of the existing services. It is highly recommended that all
         participating DSAs support this stack.

       - Use of OSI Network Service (Connection Oriented or Connectionless).

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       - X.25(80) will probably not be used in the core infrastructure of
         the Internet Directory Service, but is the basis of some European
         activities.  It may be needed later to interconnect with US
         commercial systems not on the Internet. There will be a practical
         need to interwork with DSAs which only support this stack.

       This approach has the following implications:

       1. There is a need to represent TCP/IP addresses within OSI Network
          Addresses. This is specified in RFC 1277 [HK91a].

       2. It will be desirable to have a uniform method to present Network
          Addresses of this style. Therefore, a string representation of
          presentation addresses is specified in RFC 1278 [HK91d].

       3. This approach leads to the situation where not all DSAs can
          communicate directly due the different choice of lower layers.
          This is already a practical result of many European sites operating
          DSAs over X.25.  When the Internet Directory Service is deployed,
          the issue of which DSAs operate which stacks must be considered in
          order to achieve a coherent service.  In particular, there may be a
          need to require DSAs that serve parts higher up in the DIT to serve
          multiple stacks. This will be tackled as an operational issue.

       4. There may be a requirement to extend the distributed operations, so
          that there is no requirement for full connectivity (i.e., each DSA
          supports each stack). A solution to this problem, by defining
          "relay DSAs" is specified in RFC 1276 [HK91b].

    7.3   Replication of Knowledge and Data

       There are a number of requirements on replication, both of data (the
       actual information on objects in the directory) and knowledge (the
       information on where do I find what data) information, which must be
       met before an Internet Directory can be deployed. The 1988 standard
       cannot be used as is, because it does not deal with replication or
       caching. This leads to serious problems with performance. There is a
       partial solution available in the 1992 version of the standard,
       however there are no products available yet that implement this
       solution.  These issues are discussed in more detail in RFC 1275
       [HK91c].

       As it took too long for 1992 implementations to arrive to be of any
       help to the already rapidly growing pilot that urgently needed a
       solution, an option was chosen to use a simple interim approach as
       defined in RFC 1276.  It will be clearly emphasized that this is an
       interim approach, which will be phased out as soon as the appropriate
       standards are available and stable implementations are deployed. The

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       interim approach is based on the approach used in the QUIPU
       Implementation and it is widely deployed in the existing pilots.

    7.4   Presentation of Directory Names

       The standard does not specify a means to present directory names to
       the user. This is seen as a serious deficiency, and a standard for
       presenting directory names is required. For Distinguished Names, a
       string representation is defined in [HK92a]. However, as the
       distinguished name is not very friendly for the user, a more user
       oriented specification of a standard format for representing names,
       and procedures to resolve them is chosen on the Internet, and is
       specified in [HK92b].

    7.5   DSA Naming and MD Structure

       There are some critical issues related to naming of DSAs and the
       structure of Directory Management Domains. The main issues are:

       - It is hard to achieve very high replication of knowledge
         information as this is very widely spread;

       - There is a need to give DSAs more reasonable names, which will
         contain an indication on the role of the DSA; This is necessary for
         DSAs high up the DIT.

       - There is too much DIT clutter in the current pilots;

       - There is no real concept of a DMD (Directory Management Domain)
         authority.

       These will be significant as the directory increases in size by
       orders of magnitude. The IETF OSI-DS WG is working to develop a
       solution in this area.

    8. SECURITY

       A Directory can be an important component in the overall provision of
       security in a distributed system environment, especially when
       public-key cryptographic technology is employed. The directory can
       serve as a repository for authentication information, which, in turn,
       forms the basis of a number of OSI Authentication Services (e.g.,
       X.400) and non-OSI Services (e.g., privacy-enhanced mail, PEM). The
       directory may also use this and other stored authentication
       information to provide a wide range of security Services used by the
       Directory system itself.

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    8.1   Directory Provision of Authentication

       The directory will be used to provide X.509 strong authentication.
       This places minimal requirements on the directory. To use this
       infrastructure, users of authentication services must have access to
       the directory. In practice, this type of authentication can be
       deployed only on a limited scale without use of a directory, and so
       this provision is critical for applications such as Privacy Enhanced
       Mail [Lin93]. The PEM development is considering issues relating to
       deploying Certification Authorities, and this discussion is not
       duplicated here.

       PEM defines a key management architecture based on the use of
       public-key certificates, in support of the message encipherment and
       authentication procedures defined in [Lin93]. The PEM certificate
       management design [Ken93] makes use of the authentication framework
       defined by X.509. In this framework, as adopted by PEM, a
       "certification authority" representing an organization applies a
       digital signature to a collection of data consisting of a user's
       public component, various information that serves to identify the
       user, and the identity of the organization whose signature is
       affixed.  This establishes a binding between these user credentials,
       the user's public component and the organization which vouches for
       this binding. The resulting, signed, data item is called a
       certificate. The organization identified as the certifying authority
       for the certificate is the "issuer" of that certificate. The format
       of the certificate is defined in X.509.

       In signing the certificate, the certification authority vouches for
       the user's identification, in the context specified by the identity
       of the issuer. Various types of organization may issue certificates,
       including corporate, educational, professional, or governmental
       entities. Moreover, these issuers may operate under different
       certification policies, so that not all certificates may be equally
       credible (i.e., some certificates may be more trustworthy as accurate
       identifiers of users, organizations, mailing lists, etc). The PEM
       certificate management design allows for this diversity of
       certification policies, while ensuring that any certificate can be
       traced unambiguously to the policy under which it was issued.

       The digital signature is affixed on behalf of that organization and
       is in a form which can be recognized by all members of the privacy-
       enhanced electronic mail community. This ability to universally
       verify any PEM certificate results because the PEM certification
       design is a singly rooted tree, in which the Internet Society acts as
       the root. Once generated, certificates can be stored in directory
       servers, transmitted via unsecure message exchanges, or distributed
       via any other means that make certificates easily accessible to

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    RFC 1430                     X.500 Strategy                February 1993

       message originators, without regard for the security of the
       transmission medium.

    8.2   Directory Security

       A number of security services are possible with the directory:

       Peer Authentication at Bind
          Authentication (one or two way) between DUA/DSA and DSA/DSA,
          established during the bind operation. This authentication may be
          provided using simple passwords (not recommended), one-way hashed
          passwords (more secure), or via public key cryptography (most
          secure). The various authentication options are specified in
          X.500(88), but most existent implementations implement only simple
          password authentication.

       Per-operation Authentication and Integrity
          This is usually used to identify the DUA originating an operation
          to the Directory (e.g., to authenticate prior to data
          modification). It may also be used to verify the identity of the
          DSA which provided data in a response to the user. In both
          examples, the integrity of the data also is ensured through the
          use of digital signatures. This is specified in X.500(88), but not
          yet widely implemented.

       Single Entry Access Control
          This is used to control which users (DUAs) can access and modify
          data within an entry. This is specified in X.500(92) and most DSA
          implementations provide this function.

       Multiple Entry Access Control
          This is used to control search and list operations, in order to
          allow location of information by searching, but to deter
          "trawling" of information and organizational structure. Usually,
          these access controls are limited in their ability to prevent
          trawling because of the conflicting goal of allowing a certain
          level of legitimate browsing in support of "white pages"
          functionality.

       Service Authorization
          This allows DSAs to control service in a data independent manner,
          based on peer authentication. For example, one might prevent
          students from making non-local queries, while permitting such
          queries by faculty and staff.

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    RFC 1430                     X.500 Strategy                February 1993

       Security Policy
          This term encompasses the security goals for which data access
          control, service authorization, and authentication mechanisms are
          used to implement. For example, a local security policy might
          require that all directory database modifications employ strong
          authentication and originate from a computer at a known (local)
          location.

       Data Confidentiality
          The directory does not include explicit features to protect the
          confidentiality of data while in transit (e.g., between a DUA and
          DSA or between DSAs). Instead, it is assured that lower layer
          security protocols or other local security facilities will be
          employed to provide this security service. Ongoing work on
          adaptation of the Network Layer Security Protocol (NLSP) is a
          candidate for provision of this security service with directories.

       There is no specification of any Internet-wide security policy for
       directories, nor are there currently any security mechanisms required
       of all directories. Deployment of a directory could be based on a
       variety of policies:

       - Read only system, containing only public data and restricted to
         local modification.

       - Use of X.509 authentication, and private access control mechanisms
         (this will not allow open access control management, but this is not
         seen as a fundamental problem).

       It will be important to understand if global Internet requirements
       for minimum essential directory security mechanisms will be required
       to promote widespread use of directories. We recommend that an
       informational RFC be written to analyze this issue, with an
       operational policy guidelines or applicability statement RFC to
       follow.

    9. RELATION TO DNS

       It is important to establish the relationship between the proposed
       Internet Directory, and the existing Domain Name System. An
       Experimental Protocol RFC (RFC 1279) proposes a mapping of DNS
       information onto the Directory. Experiments should be conducted in
       this area [HK91e].

    10. EXTERNAL CONNECTIONS

       It will be important for this activity to maintain suitable external
       liaisons. In particular to:

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    RFC 1430                     X.500 Strategy                February 1993

       Other Directory Services and Directory Pilots

          To ensure a service which is coherent with other groups building
          X.500 services. e.g.,:

          -  Paradise
          -  NADF
          -  FOX
          -  PSI White Pages

       Standards Bodies

          To feed back experience gained from this activity, so that the
          next round of standards meets as many of the Internet requirements
          as possible. e.g.,:

          -  CCITT/ISO
          -  RARE WG-NAS
          -  EWOS/OIW
          -  ETSI

    11. REFERENCES

       [BHK91a]  Barker, P., and S. Hardcastle-Kille, "The COSINE and
                 Internet X.500 Schema", RFC 1274, Department of Computer
                 Science, University College London, November 1991.

       [BHK92]   Barker, P., and S. Hardcastle-Kille, "Naming Guidelines for
                 Directory Pilots", RFC 1384, Department of Computer Science,
                 University College London, ISODE Consortium, January 1993.

       [CCI88a]  The Directory --- authentication framework, December 1988.
                 CCITT Recommendation X.509.

       [CCI88b]  The Directory --- overview of concepts, models and services,
                 December 1988. CCITT X.500 Series Recommendations.

       [CCI90]   The Directory --- part 9 --- replication, October 1990.
                 ISO/IEC CD 9594-9 Ottawa output.

       [CFSD90]  Case, J., Fedor, M., Schoffstall, M., and J. Davin, "A
                 Simple Network Management Protocol", STD 15, RFC 1157,
                 SNMP Research, Performance Systems International, MIT
                 Laboratory for Computer Science, May 1990.

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    RFC 1430                     X.500 Strategy                February 1993

       [For91]   The North American Directory Forum, "A Naming Scheme
                 for C=US", RFC 1255, NADF, September 1991.
                 Also NADF-175.  (See also RFC 1417.)

       [For92]   The North American directory Forum, "User Bill of Rights
                 for Entries and Listing in the Public Directory", RFC 1295,
                 NADF, January 1992.  (See also RFC 1417.)

       [HK91a]   Hardcastle-Kille, S., "Encoding network addresses to
                 support operation over non-OSI lower layers", RFC 1277,
                 Department of Computer Science, University College London,
                 November 1991.

       [HK91b]   Hardcastle-Kille, S., "Replication and distributed
                 operations extensions to provide an internet directory
                 using X.500", RFC 1276, Department of Computer Science,
                 University College London, November 1991.

       [HK91c]   Hardcastle-Kille, S., "Replication requirement to
                 provide an internet directory using X.500", RFC 1275,
                 Department of Computer Science, University College
                 London, November 1991.

       [HK91d]   Hardcastle-Kille, S., "A string encoding of presentation
                 address", RFC 1278, Department of Computer Science,
                 University College London, November 1991.

       [HK91e]   Hardcastle-Kille, S., "X.500 and domains", RFC 1279,
                 Department of Computer Science, University College
                 London, November 1991.

       [HK92a]   Hardcastle-Kille, S., "A string representation of
                 Distinguished Names", Department of Computer Science,
                 University College London, Work in Progress.

       [HK92b]   Hardcastle-Kille, S., "Using the OSI directory to achieve
                 user friendly naming", Department of Computer Science,
                 University College London, Work in Progress.

       [HSB91]   Howes, R., Smith, M., and B. Beecher, "DIXIE Protocol
                 Specification", RFC 1249, University of Michigan,
                 July 1991.

       [ISO]     Procedures for the operation of OSI registration
                 authorities --- part 1: general procedures. ISO/IEC 9834-1.

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    RFC 1430                     X.500 Strategy                February 1993

       [Ken93]   Kent, S., "Privacy Enhancement for Internet Electronic
                 Mail: Part II - Certificate-based Key Management, RFC 1422,
                 BBN, February 1993.

       [Kil88]   Kille, S., "The QUIPU Directory Service", In IFIP WG 6.5
                 Conference on Message Handling Systems and Distributed
                 Applications, pages 173--186. North Holland Publishing,
                 October 1988.

       [Kil89]   Kille, S., "The THORN and RARE Naming Architecture",
                 Technical report, Department of Computer Science,
                 University College London, June 1989. THORN Report UCL-64
                 (version 2).

       [Lin93]   Linn, J., "Privacy Enhancement for Internet Electronic
                 Mail: Part I - Message Encryption and Authentication
                 Procedures", RFC 1421, February 1993.

       [LW91]    Lang, R., and R. Wright, "A Catalog of Available X.500
                 Implementations", FYI 11, RFC 1292, SRI International,
                 Lawrence Berkeley Laboratory, January 1992.

       [Lyn91]   Lynch, C., "The Z39.50 information retrieval protocol: An
                 overview and status report", Computer Communication Review,
                 21(1):58--70, January 1991.

       [Par91]   Paradise International Report, Cosine. Paradise project,
                 Department of Computer Science, University College London.
                 November 1991.

       [RC87]    Rose, M., and D. Cass, "ISO Transport Services on
                 top of the TCP", STD 35, RFC 1006, Northrop Corporation
                 Technology Center, May 1987.

       [Ros91]   Rose, M., "Directory Assistance Service", RFC 1202,
                 Performance Systems International, February 1991.

       [WR92]    Weider, C., and J. Reynolds, "Executive Introduction to
                 Directory Services Using the X.500 Protocol", FYI 13,
                 RFC 1308, ANS, ISI, March 1992.

    12.  Security Considerations

       Security issues are discussed in Section 8.

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    13. Authors' Addresses

       Steve Hardcastle-Kille
       ISODE Consortium
       PO box 505
       SW11 1DX London
       England
       Phone: +44-71-223-4062
       EMail: S.Kille@isode.com

       Erik Huizer
       SURFnet bv
       PO box 19035
       3501 DA Utrecht
       The Netherlands
       Phone: +31-30 310290
       Email: Erik.Huizer@SURFnet.nl

       Vinton Cerf
       Corporation for National Research Initiatives
       1895 Preston White Drive, Suite 100
       Reston, VA 22091
       Phone: (703) 620-8990
       EMail: vcerf@cnri.reston.va.us

       Russ Hobby
       University of California, Davis
       Computing Services
       Surge II Room 1400
       Davis, CA 95616
       Phone: (916) 752-0236
       EMail: rdhobby@ucdavis.edu

       Steve Kent
       Bolt, Beranek, and Newman
       50 Moulton Street
       Cambridge, MA 02138
       Phone: (617) 873-3988
       EMail: skent@bbn.com

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