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