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rfc:rfc1430

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

Hardcastle-Kille, Huizer, Cerf, Hobby & Kent [Page 1] RFC 1430 X.500 Strategy February 1993

 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:
  1. White Pages lookup of users;
  1. 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:
  1. General resource lookup, for information ranging from committee

structures to bibliographic data;

  1. Support of management of the Internet infrastructure, and

integration of configuration information into the higher level

   directory;
  1. 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.
  1. 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).

Hardcastle-Kille, Huizer, Cerf, Hobby & Kent [Page 2] RFC 1430 X.500 Strategy February 1993

 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:

Hardcastle-Kille, Huizer, Cerf, Hobby & Kent [Page 3] RFC 1430 X.500 Strategy February 1993

  1. 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;
  1. Each object in this information structure (called the Directory

Information Tree, DIT) is represented as an entry;

  1. Objects are typed by an "object class", which permits multiple

inheritance;

  1. An object is described by a set of attributes;
  1. Each attribute is typed. Attribute types are hierarchical;
  1. 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.
  1. Each entry has an unambiguous and unique global name;
  1. 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:
  1. Support of ordered attributes (needed by some applications such as

message storage);

  1. Extensions to allow unification with management information,

associated with SNMP (Simple Network Management Protocol) [CFSD90]

   or other management protocols;
  1. 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.

Hardcastle-Kille, Huizer, Cerf, Hobby & Kent [Page 4] RFC 1430 X.500 Strategy February 1993

 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:
  1. Defining the naming hierarchy; See section 4.
  2. Creating the Directory Infrastructure; See section 5.
  3. Getting the Data into the directory; and
  4. 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).

Hardcastle-Kille, Huizer, Cerf, Hobby & Kent [Page 5] RFC 1430 X.500 Strategy February 1993

 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.

Hardcastle-Kille, Huizer, Cerf, Hobby & Kent [Page 6] 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

  1. 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.

Hardcastle-Kille, Huizer, Cerf, Hobby & Kent [Page 7] RFC 1430 X.500 Strategy February 1993

    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.
  1. 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].
  1. 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].
  1. 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.
  1. 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.
  1. 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.
  1. 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

Hardcastle-Kille, Huizer, Cerf, Hobby & Kent [Page 8] RFC 1430 X.500 Strategy February 1993

   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.
  1. 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

  1. Enhanced performance is necessary to allow for a real global usage;
  1. The schema has to be extended to allow for various kinds of data,

e.g.,:

    o  NIC data;
    o  Resource location;
  1. 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

  1. 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.
  1. Interface existing RDBMS into the Directory Service.
  1. 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.

Hardcastle-Kille, Huizer, Cerf, Hobby & Kent [Page 9] RFC 1430 X.500 Strategy February 1993

 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.

Hardcastle-Kille, Huizer, Cerf, Hobby & Kent [Page 10] RFC 1430 X.500 Strategy February 1993

 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:
  1. Operation on top of TCP/IP using a lightweight protocol.
  1. 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.
  1. Use of OSI Network Service (Connection Oriented or Connectionless).

Hardcastle-Kille, Huizer, Cerf, Hobby & Kent [Page 11] RFC 1430 X.500 Strategy February 1993

  1. 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

Hardcastle-Kille, Huizer, Cerf, Hobby & Kent [Page 12] RFC 1430 X.500 Strategy February 1993

 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:
  1. It is hard to achieve very high replication of knowledge

information as this is very widely spread;

  1. 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.
  1. There is too much DIT clutter in the current pilots;
  1. 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.

Hardcastle-Kille, Huizer, Cerf, Hobby & Kent [Page 13] RFC 1430 X.500 Strategy February 1993

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

Hardcastle-Kille, Huizer, Cerf, Hobby & Kent [Page 14] 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.

Hardcastle-Kille, Huizer, Cerf, Hobby & Kent [Page 15] 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:
  1. Read only system, containing only public data and restricted to

local modification.

  1. 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:

Hardcastle-Kille, Huizer, Cerf, Hobby & Kent [Page 16] 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.,:
  1. Paradise
  2. NADF
  3. FOX
  4. 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.,:
  1. CCITT/ISO
  2. RARE WG-NAS
  3. EWOS/OIW
  4. 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.

Hardcastle-Kille, Huizer, Cerf, Hobby & Kent [Page 17] 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.

Hardcastle-Kille, Huizer, Cerf, Hobby & Kent [Page 18] 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.

Hardcastle-Kille, Huizer, Cerf, Hobby & Kent [Page 19] RFC 1430 X.500 Strategy February 1993

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

Hardcastle-Kille, Huizer, Cerf, Hobby & Kent [Page 20]

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