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rfc:rfc3650

Network Working Group S. Sun Request for Comments: 3650 L. Lannom Category: Informational B. Boesch

                                                                  CNRI
                                                         November 2003
                      Handle System Overview

Status of this Memo

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

Copyright Notice

 Copyright (C) The Internet Society (2003).  All Rights Reserved.

IESG Note

 Several groups within the IETF and IRTF have discussed the Handle
 System and its relationship to existing systems of identifiers.  The
 IESG wishes to point out that these discussions have not resulted in
 IETF consensus on the described Handle System, nor on how it might
 fit into the IETF architecture for identifiers.  Though there has
 been discussion of handles as a form of URI, specifically as a URN,
 these documents describe an alternate view of how namespaces and
 identifiers might work on the Internet and include characterizations
 of existing systems which may not match the IETF consensus view.

Abstract

 This document provides an overview of the Handle System in terms of
 its namespace and service architecture, as well as its relationship
 to other Internet services such as DNS, LDAP/X.500, and URNs.  The
 Handle System is a general-purpose global name service that allows
 secured name resolution and administration over networks such as the
 Internet.  The Handle System manages handles, which are unique names
 for digital objects and other Internet resources.

Sun, et al. Informational [Page 1] RFC 3650 Handle System Overview November 2003

Table of Contents

 1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  2
 2.  Motivations. . . . . . . . . . . . . . . . . . . . . . . . . .  6
 3.  Handle Namespace . . . . . . . . . . . . . . . . . . . . . . .  7
 4.  Handle System Architecture . . . . . . . . . . . . . . . . . .  8
 5.  Handle System Security . . . . . . . . . . . . . . . . . . . . 11
 6.  The Handle System and other Internet Services. . . . . . . . . 12
     6.1.  Domain Name Service (DNS). . . . . . . . . . . . . . . . 13
     6.2.  Directory Services (X.500/LDAP). . . . . . . . . . . . . 13
     6.3.  Uniform Resource Identifier (URI)/Uniform Resource Name
           (URN). . . . . . . . . . . . . . . . . . . . . . . . . . 14
 7.  Security Considerations. . . . . . . . . . . . . . . . . . . . 15
     7.1.  General Security Practice. . . . . . . . . . . . . . . . 15
     7.2.  Privacy Protection . . . . . . . . . . . . . . . . . . . 16
     7.3.  Caching and Proxy Servers. . . . . . . . . . . . . . . . 16
     7.4.  Mirroring. . . . . . . . . . . . . . . . . . . . . . . . 17
     7.5.  Denial of Service (DoS). . . . . . . . . . . . . . . . . 17
 8.  History of the Handle System . . . . . . . . . . . . . . . . . 18
 9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 18
 10. References and Bibliography. . . . . . . . . . . . . . . . . . 19
 11. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 20
 12. Full Copyright Statement . . . . . . . . . . . . . . . . . . . 21

1. Introduction

 This document provides an overview of the Handle System, a
 distributed information system designed to provide an efficient,
 extensible, and secured global name service for use on networks such
 as the Internet.  The Handle System includes an open protocol, a
 namespace, and a reference implementation of the protocol.  The
 protocol enables a distributed computer system to store names, or
 handles, of digital resources and resolve those handles into the
 information necessary to locate, access, and otherwise make use of
 the resources.  These associated values can be changed as needed to
 reflect the current state of the identified resource without changing
 the handle.  This allows the name of the item to persist over changes
 of location and other current state information.  Each handle may
 have its own administrator(s) and administration can be done in a
 distributed environment.  The Handle System supports secured handle
 resolution.  Security services such as data confidentiality, data
 integrity, and non-repudiation are provided upon client request.
 The Handle System provides a confederated name service that allows
 any existing local namespace to join the global handle namespace by
 obtaining a unique Handle System naming authority.  Local names and
 their value-binding(s) remains intact after joining the Handle
 System.  Any handle request to the local namespace may be processed

Sun, et al. Informational [Page 2] RFC 3650 Handle System Overview November 2003

 by a service interface speaking the Handle System protocol.  Combined
 with the unique naming authority, any local name is guaranteed unique
 under the global handle namespace.
 There are several services used today to provide name service for
 Internet resources.  Among these, the Domain Name System (DNS) [2,3]
 is the most widely used.  DNS is designed "to provide a mechanism for
 naming resources in such a way that the names are mappable into IP
 addresses and are usable in different hosts, networks, protocol
 families, internets, and administrative organizations" [3].  The
 growth of the Internet has raised demands for various extensions to
 DNS.  There are also attempts to use DNS as a general-purpose
 resource naming system.  However, the importance of DNS in basic
 network routing has led to great caution in implementing any DNS
 extension or overloading the DNS for general-purpose resource naming.
 An additional factor which argues against using DNS as a general-
 purpose naming service is the DNS administrative model.  DNS names
 are typically managed by the network administrator(s) at the DNS zone
 level.  There is no provision for per-name administrative structure
 and no facilities for anyone other than the network administrator to
 create or manage DNS names.  This is appropriate for domain name
 administration, but less so for general-purpose resource naming.
 The Handle System has been designed from the start to serve as a
 general-purpose naming service.  It is designed to accommodate very
 large numbers of entities and to allow distributed administration
 over the public Internet.  The Handle System data model allows access
 control to be defined at the level of each of the data values
 associated with a given handle.  Each handle can further define its
 own set of administrators that are independent from the network or
 host administrator.
 Traditional URLs (Uniform Resource Locators) [4] allow certain
 Internet resources to be named as a combination of a DNS name and
 local name.  The local name may be a local file path, or a reference
 to some local service (e.g., a cgi-bin script).  This combination of
 a DNS name and a local name provides a flexible administrative model
 for naming and managing individual Internet resources.  However, the
 URL practice also has some key limitations.  Most URL schemes (e.g.,
 http) are defined for resolution only.  Any URL administration has to
 be done either at the local host, or via some other network service
 such as NFS.  Using a URL as a name typically ties the Internet
 resource to its current network location.  For example, a URL will be
 tied to its local file path when the file path is part of the URL.
 When the resource moves from one location to another for whatever
 reason, the URL breaks.  It is especially difficult to work around

Sun, et al. Informational [Page 3] RFC 3650 Handle System Overview November 2003

 this problem when the reason for the location change is change in
 ownership of an asset, as ownership is generally reflected in the
 domain name.
 The Handle System is designed to overcome these limitations and to
 add significant functionality.  Specifically, the Handle System is
 designed with the following objectives:
  1. Uniqueness: Every handle is globally unique within the Handle

System.

  1. Persistence: Handles may be used as persistent identifiers for

Internet resources. A handle does not have to be derived from

       the entity that it names.  While an existing name, or even a
       mnemonic, may be included in a handle for convenience, the only
       operational connection between a handle and the entity it names
       is maintained within the Handle System.  This of course does
       not guarantee persistence, which is a function of
       administrative care.  But it does allow the same name to
       persist over changes of location, ownership, and other state
       conditions.  For example, when a named resource moves from one
       location to another, the handle may be kept valid by updating
       its value in the Handle System to reflect the new location.
  1. Multiple Instances: A single handle can refer to multiple

instances of a resource, at different and possibly changing

       locations in a network.  Applications can take advantage of
       this to increase performance and reliability.  For example, a
       network service may define multiple entry points for its
       service with a single handle so as to distribute the service
       load.
  1. Multiple Attributes: A single handle can refer to multiple

attributes of a resource, including associated services,

       available through any method at different and possibly changing
       network locations.  Handles can thus be used as persistent
       entry points into an evolving world of services associated with
       identified resources.
  1. Extensible Namespace: Existing local namespaces may join the

handle namespace by acquiring a unique handle naming authority.

       This allows local namespaces to be introduced into a global
       context while avoiding conflict with existing namespaces.  Use
       of naming authorities also allows delegation of service, both
       resolution and administration, to a local handle service.

Sun, et al. Informational [Page 4] RFC 3650 Handle System Overview November 2003

  1. International Support: The handle namespace is based on Unicode

3.0 [17], which includes most of the characters currently used

       around the world.  This allows handles to be used in any native
       environment.  The handle protocol mandates UTF-8 [5] as the
       encoding used for handles.
  1. Distributed Service Model: The Handle System defines a

hierarchical service model such that any local handle namespace

       may be serviced by a corresponding local handle service, by the
       global service, or by both.  The global service, known as the
       Global Handle Registry, can be used to dispatch any handle
       service request to the responsible local handle service.  The
       distributed service model allows replication of any given
       service into multiple service sites, and each service site may
       further distribute its service into a cluster of individual
       servers.  (Note that local here refers only to namespace and
       administrative concerns.  A local handle service could in fact
       have many service sites distributed across the Internet.)
  1. Secured Name Service: The Handle System allows secured name

resolution and administration over the public Internet. The

       Handle System protocol defines standard mechanisms for both
       client and server authentication, as well as service
       authorization.  It also provides security options to assure
       data integrity and confidentiality.
  1. Distributed Administration Service: Each handle may define its

own administrator(s) or administrator group(s). Ownership of

       each handle is defined in terms of its administrator or
       administrator groups.  This, combined with the Handle System
       authentication protocol, allows any handle to be managed
       securely over the public network by its administrator at any
       network location.
  1. Efficient Resolution Service: The handle protocol is designed

to allow highly efficient name resolution performance. To

       avoid resolution being affected by computationally costly
       administration service, separate service interfaces (i.e.,
       server processes and their associated communication ports) for
       handle name resolution and administration may be defined by any
       handle service.
 This document provides an overview of the handle namespace and
 service architecture.  It also compares the Handle System with other
 existing Internet services, protocols, and specifications (e.g., DNS
 [2, 3], URLs [4], X.500/LDAP [6,7,8], and URN [9,10]).  Details of
 the handle system data and service model, as well as its
 communication protocol, are specified in separate documents.  They

Sun, et al. Informational [Page 5] RFC 3650 Handle System Overview November 2003

 can be found under the Handle System website at
 http://www.handle.net.

2. Motivations

 Since there are a number of name related projects in the Internet
 community, it is worth defining exactly where we believe the Handle
 System fits.  Unfortunately, that is particularly hard because the
 other primary naming schemes either take an abstract services
 approach (e.g., URI/URN), or an approach to name resolution absent of
 a self-contained framework for reliable yet distributed
 administration of the underlying databases (e.g., DNS).  This makes
 categorizing the Handle System difficult.
 The Handle System crosses boundaries.  Looked at as a name resolution
 system, it might be compared to DNS.  If used to implement a URI/URN
 namespace, it could be used with any URI/URN scheme.  If used for
 distributed information updates and administration, it could be
 considered a simplified-version of a distributed database system.
 It is probably best to view the Handle System as a name-attribute
 binding service with a specific protocol for securely creating,
 updating, maintaining, and accessing a distributed database.  It is
 designed to be an enabling service for secured information and
 resource sharing over networks such as the public Internet.
 Applications of the Handle System could include meta-data services
 for digital publications, identity management services for virtual
 identities, or any other applications that require resolution and/or
 administration of globally unique identifiers.
 In the spirit of exploration, the Handle System has been designed to
 have high performance for name resolution and to push the boundaries
 of distributed access control and administration.  Unlike most
 conventional systems (even distributed systems) that are designed to
 have a relatively small number of broadly empowered administrators,
 the Handle System allows extremely fine granularity of administrative
 control.  It has a unique self-contained administrative framework
 that de-couples the ownership of each handle from the system
 administrators and allows access control to be defined for each
 handle value.
 It should be noted, that as with all real systems, the Handle System
 is a compromise between a number of technical and practical concerns.
 There are also different opinions within the IETF on where the Handle
 System fits in relation to other existing Internet name services.  It
 is with the goal of exposing a broader community to the concepts,
 approach, specific decisions, tradeoffs and results that we are
 writing this RFC.

Sun, et al. Informational [Page 6] RFC 3650 Handle System Overview November 2003

3. Handle Namespace

 Every handle consists of two parts: its naming authority, otherwise
 known as its prefix, and a unique local name under the naming
 authority, otherwise known as its suffix:
    <Handle> ::= <Handle Naming Authority> "/" <Handle Local Name>
 The naming authority and local name are separated by the ASCII
 character "/".  The collection of local names under a naming
 authority defines the local handle namespace for that naming
 authority.  Any local name must be unique under its local namespace.
 The uniqueness of a naming authority and a local name under that
 authority ensures that any handle is globally unique within the
 context of the Handle System.
 For example, "10.1045/january99-bearman" is a handle for an article
 published in D-Lib magazine [12].  Its naming authority is "10.1045"
 and its local name is "january99-bearman".  The handle namespace can
 be considered a superset of many local namespaces, with each local
 namespace having a unique naming authority under the Handle System.
 The naming authority identifies the administrative unit of creation,
 although not necessarily continuing administration, of the associated
 handles.  Each naming authority is guaranteed to be globally unique
 within the Handle System.  Any existing local namespace can join the
 global handle namespace by obtaining a unique naming authority so
 that any local name under the namespace can be globally referenced as
 a combination of the naming authority and the local name as shown
 above.
 Naming authorities under the Handle System are defined in a
 hierarchical fashion resembling a tree structure.  Each node and leaf
 of the tree is given a label that corresponds to a naming authority
 segment.  The parent node notifies the parent naming authority of its
 child nodes.  Unlike DNS, handle naming authorities are constructed
 left to right, concatenating the labels from the root of the tree to
 the node that represents the naming authority.  Each label is
 separated by the octet used for ASCII character "." (0x2E).  For
 example, a naming authority for the National Digital Library Program
 ("ndlp") at the Library of Congress ("loc") is defined as "loc.ndlp".
 Each naming authority may have many child naming authorities
 registered underneath.  Any child naming authority can only be
 registered by its parent after its parent naming authority has been
 registered.  However, there is no intrinsic administrative
 relationship between the namespaces represented by the parent and
 child naming authorities.  The parent namespace and its child

Sun, et al. Informational [Page 7] RFC 3650 Handle System Overview November 2003

 namespaces may be served by different handle services, and they may
 or may not share any administration privileges.
 Handles may consist of any printable characters from the Universal
 Character Set (UCS-2) of ISO/IEC 10646, which is the exact character
 set defined by Unicode v3.0 [17].  The UCS-2 character set
 encompasses most characters used in every major language written
 today.  To allow compatibility with most of the existing systems and
 to prevent ambiguity among different encodings, the Handle System
 protocol mandates UTF-8 to be the only encoding used for handles.
 The UTF-8 encoding preserves any ASCII encoded names so as to allow
 maximum compatibility with existing systems without causing naming
 conflict.  Some encoding issues over the global namespace and the
 choice of UTF-8 encoding are discussed in [13].
 By default, handles are case sensitive.  However, any individual
 handle service may define its namespace such that ASCII characters
 within any handle under that namespace are case insensitive.

4. Handle System Architecture

 The Handle System defines a hierarchical service model.  The top
 level consists of a single handle service, known as the Global Handle
 Registry (GHR).  The lower level consists of all other handle
 services, generically known as Local Handle Services (LHS).
 The Global Handle Registry can be used to manage any handle
 namespace.  It is unique among handle services only in that it
 provides the service used to manage naming authorities, all of which
 are managed as handles.  The naming authority handle provides
 information that clients can use to access and utilize the local
 handle service for handles under the naming authority.
 Local Handle Services are intended to be hosted by organizations with
 administrative responsibility for handles under certain naming
 authorities.  A Local Handle Service may be responsible for any
 number of local handle namespaces, each identified by a unique naming
 authority.  The Local Handle Service and its responsible set of local
 handle namespaces must be registered with the Global Handle Registry.
 One important aspect of the Handle System is its distributed
 architecture.  The Handle System as a whole consists of a number of
 individual handle services.  Each of these services may consist of
 one or more service sites.  Each service site is a complete
 replication of every other site in the service in terms of handle
 resolution.  Each service site may consist of one or more handle
 servers.  All handles, and hence all handle requests, directed at a
 given service site will be evenly distributed across these handle

Sun, et al. Informational [Page 8] RFC 3650 Handle System Overview November 2003

 servers.  The Handle System as a whole may consist of any number of
 handle services.  There are no design limits on the number of handle
 services or on the number of sites which make up each service, nor
 are there any limits on the number of servers that make up each site.
 Replication among any service site does not require that each site
 contain the same number of servers.  In other words, while each site
 will have the same replicated set of handles, each site may allocate
 that set of handles across a different number of servers.  This
 distributed approach is intended to aid scalability, accommodate any
 large-scale of operation, and mitigate problems of single point
 failure.
 Figure 3.1 illustrates a potential handle service that consists of
 two service sites: one located on the U.S. east coast and the other
 on the U.S. west coast.  The east coast service site consists of four
 server computers.  The west coast service site, with more powerful
 computers deployed, decides two servers will suffice.  The number of
 service sites for any handle service, as well as the number of
 servers that are used by any service site, may be added or removed
 dynamically depending on the service requirement.
  1. ———————— ——————

| ——— ——— | | —– —– |

    | |         | |         | |            | |  S  |  |  S  | |
    | | server1 | | server2 | |            | |  E  |  |  E  | |
    | |         | |         | |            | |  R  |  |  R  | |
    |  ---------   ---------  |            | |  V  |  |  V  | |
    |  ---------   ---------  |            | |  E  |  |  E  | |
    | |         | |         | |            | |  R  |  |  R  | |
    | | Server3 | | Server4 | |            | |     |  |     | |
    | |         | |         | |            | |  1  |  |  2  | |
    |  ---------   ---------  |            |  -----    -----  |
     -------------------------               ------------------
       Handle Service Site 1                Handle Service Site 2
          (US East Coast)                     (US West Coast)
     Figure 3.1: Handle service configured with two service sites
 Each handle service manages a distinct sub-namespace under the Handle
 System.  Namespaces under different handle services may not overlap.
 The sub-namespace typically consists of handles under a number of
 naming authorities.  The handle service is called the "home" service
 of these naming authorities and is the only one that provides
 resolution and administration service for handles under these naming
 authorities.  Before resolving a handle, a client has to determine
 the "home" service of the handle in question.  The "home" service of
 each handle is the "home" service of its naming authority and is

Sun, et al. Informational [Page 9] RFC 3650 Handle System Overview November 2003

 registered at the Global Handle Registry.  Clients can find the
 "home" service for each handle by querying the naming authority
 handle at the Global Handle Registry.
 The Global Handle Registry maintains naming authority handles.  Each
 naming authority handle maintains the service information that
 describes the "home" service of the naming authority.  The service
 information lists the service sites of the given handle service, as
 well as the interface to each handle server within each site.  To
 find the "home" service for any handle, a client can query the Global
 Handle Registry for the service information associated with the
 corresponding naming authority handle.  The service information
 provides the necessary information for clients to communicate with
 the "home" service.
 Figure 3.2 shows an example of a typical handle resolution process.
 In this case, the "home" service is a Local Handle Service.  The
 client is trying to resolve the handle "10.1045/july95-arms" and has
 to find its "home" service from the Global Handle Registry.  The
 "home" service can be found by sending a query to the Global Handle
 Registry for the naming authority handle for "10.1045".  The Global
 Handle Registry returns the service information of the Local Handle
 Service that is responsible for handles under the naming authority
 "10.1045".  The service information allows the client to communicate
 with the Local Handle Service to resolve the handle "10.1045/july95-
 arms".

Sun, et al. Informational [Page 10] RFC 3650 Handle System Overview November 2003

  1. ———————–

| | 4. Result of client request

    | Client with global     |  <-------------------------------.
    |  service information   |                                  |
    |                        |  ----------------------------.   |
     ------------------------     3. Request to responsible |   |
               |   ^                 Local Handle Service   |   |
   1. Client   |   |                                        |   |
   query for   |   |                                        |   |
   naming      |   | 2. Service information                 |   |
   authority   |   |    for "10.1045"                       V   |
   "10.1045"   |   |                          ----------------------
               |   |                         |                      |
               V   |                         | Local Handle Service |
          ---------------                    | responsible for the  |
         |               |                   | naming authority     |
         | Global Handle |                   | "10.1045"            |
         |   Registry    |                   |                      |
         |               |                    ----------------------
          ---------------
             Figure 3.2: Handle resolution starting with global
 To improve resolution performance, any client may choose to cache the
 service information returned from the Global Handle Registry and use
 it for subsequent queries.  A separate handle caching server, either
 stand-alone or as a piece of a general caching mechanism, may also be
 used to provide shared caching within a local community.  Given a
 cached resolution result, subsequent queries of the same handle may
 be answered locally without contacting any handle service.  Given
 cached service information, clients can send their requests directly
 to the correct Local Handle Service without contacting the Global
 Handle Registry.

5. Handle System Security

 The Handle System provides handle resolution and administration
 service over networks such as the public Internet.  Each handle can
 be assigned a set of values.  Clients use the handle resolution
 service to resolve any handle into its set of values.  Each value has
 a data type and a unique value index.  Clients can query for specific
 handle values based on data type or value index.
 The handle administration service answers requests from clients to
 manage handles.  These include adding handles, deleting handles or
 updating their values.  It also manages naming authorities via naming
 authority handles.  Each handle can have its own administrator(s),
 and each administrator can be granted a certain set of permissions.

Sun, et al. Informational [Page 11] RFC 3650 Handle System Overview November 2003

 The handle system authentication protocol authenticates the handle
 administrator before fulfilling any administrative request.
 The Handle System provides security services such as client and
 server authentication, data confidentiality and integrity, and non-
 repudiation.  By default, handle resolution does not require any
 client authentication.  However, resolution requests for confidential
 data assigned to any handle (by its administrator), as well as any
 administration requests (e.g., adding or deleting handle values)
 require authentication of the client for proper authorization.  The
 server will decide, during the authorization process, whether or not
 the client has permission to access those confidential handle values,
 or has permission to add or update handles and handle values.  When
 authentication is required, the handle server will issue a challenge
 to the requesting client before carrying out the client's request.
 To satisfy the authentication requirement, the client must send back
 the correct response identifying itself as a qualified administrator.
 The handle server will respond to the initial request only after
 successful authentication of the client.  Handle clients may choose
 to use either secret key or public key cryptography for
 authentication.  Handle System authentication can also be carried out
 via third party authentication services.  To ensure data integrity,
 clients may request digitally signed responses from any handle
 server.  They may also set up secured communication sessions with
 handle servers so that any exchanged information can be encrypted
 (for data confidentiality) using a session key.  Handle servers can
 also provide confidentiality by encrypting the handle data before
 sending it to the client.
 The Handle System provides service options for secured information
 exchange between the client and server.  This does not, of course,
 guarantee the truthfulness of handle values.  Incorrect values
 assigned to any handle by its administrator may very well mislead
 clients.  On the other hand, a handle value may contain references to
 other handle values to provide additional credentials.  For example,
 a handle value R (e.g., a claim) may contain a reference to some
 other handle value that contains the digital signature (from a
 creditable source) upon the value R.  Clients who trust the signature
 could then trust the handle value R.

6. The Handle System and other Internet Services

 There are a number of existing and proposed Internet identifier
 services or specifications that, by design or intent, cover some of
 the functionalities proposed for the Handle System.  This section
 briefly reviews them in relationship to the Handle System.

Sun, et al. Informational [Page 12] RFC 3650 Handle System Overview November 2003

6.1. Domain Name Service (DNS)

 The Domain Name Service, or DNS, was originally designed and is
 heavily used for mapping domain names into IP Addresses for network
 routing purposes.  RFC 1034 [2] and RFC 1035 [3] provide detailed
 descriptions of its design and implementation.  The growth of the
 Internet has increased demands for various extensions to DNS, even
 its possible use as a general purpose resource naming system.
 However, any such use has the potential to slow down the network
 address translation and/or affect its effectiveness in network
 routing.  DNS implementations typically do not scale well when a
 large amount of data is associated with any particular DNS name.  It
 is therefore generally considered inappropriate to use DNS as a
 general-purpose naming service.
 An additional factor that argues against using DNS as a general-
 purpose naming service is the DNS administrative model.  DNS names
 are typically managed by the network administrator(s) at the DNS zone
 level.  There is no provision for a per-name administrative
 structure.  No facilities are provided for anyone other than network
 administrators to create or manage DNS names.  This is appropriate
 for domain name administration but less so for general-purpose name
 administration.
 The Handle System differs from DNS in its distributed administration
 and service model, as well as its security features.  The handle
 system protocol includes security options to assure confidentiality
 and integrity during data transmission.  Each handle can have its own
 administrator, independent from the server administrator.  The handle
 system protocol allows any handle administrator to manage his or her
 handles securely over the public network.  Additionally, the Handle
 System service model allows any of its service sites to dynamically
 configure its service distribution among a cluster of servers to
 accommodate increased service requests.  This also allows less
 powerful computers to be used together to support any arbitrarily
 large number of handles.

6.2. Directory Services (X.500/LDAP)

 X.500 [6] is the OSI Directory Standard defined by the ISO and the
 ITU.  It is designed "to provide a white pages service that would
 return either the telephone numbers or X.400 O/R addresses of
 people", and is "concerned mainly with providing the name server
 service for Open Systems Interconnection (OSI) applications" [7].
 X.500 defines a hierarchical data and information model with a set of
 protocols to allow global name lookup and search.  The protocol,
 however, has proved difficult to implement and there has been
 difficulty in getting "client access integrated into existing

Sun, et al. Informational [Page 13] RFC 3650 Handle System Overview November 2003

 products" [14].  LDAP (Lightweight Directory Access Protocol) [8] has
 overcome many of these difficulties by making the protocol simpler
 and easier to implement.  Some concern remains, however, that as LDAP
 is emerging from a local directory access protocol (LDAP v2) into a
 distributed service protocol (LDAP v3), it faces many issues not
 addressed in its original design, resulting in new complications.
 The fundamental difference between a name resolution service such as
 the Handle System, and a directory service such as LDAP, is search
 capability.  The added functionality of being able to search a
 directory service necessarily carries with it added complexity, thus
 affects its efficiency.  A pure name service, such as the Handle
 System, can be designed solely around efficient resolution of known
 items without addressing functions and data structures required for
 discovery of unknown items based on incomplete criteria.
 Directory services, such as LDAP or WHOIS++ [15,16], may be used in
 tandem with the Handle System to provide reverse lookup service.
 Existing corporate directory services, for example, could provide
 interfaces to both services.  The Handle System interface would
 provide a highly efficient name resolution service.  The directory
 service interface would provide extended search capability.  Handles
 could also be used in LDAP service referral.  For example, an LDAP
 service may be referenced as a handle.  Doing so will make the
 reference persistent overtime, independent of location change.

6.3. Uniform Resource Identifier (URI)/Uniform Resource Name(URN)

 Uniform Resource Identifier (URI) [23] defines a uniform, yet
 extensible naming mechanism for identifying Internet resources in web
 applications.  Uniform Resource Name (URN) [11], a subset of URI,
 defines a namespace registration mechanism for persistent namespaces
 under URI.  URI/URN represents most of the Internet name services
 used in web applications.  This section discusses the relationship of
 the Handle System to URI/URN and how applications may utilize the
 Handle System within the URI/URN context.
 The Handle System provides a general-purpose name service for the
 Internet.  Like DNS or X.500 directory service, the Handle System
 defines its namespace outside of any URI/URN namespace.  Handles can
 be transcribed and resolved directly, without any URI/URN scheme as a
 prefix.  For example, a library application may resolve the handle
 "10.1045/july95-arms" directly into its set of handle values.  No
 URI/URN scheme will be needed in this case.
 The Handle System may be used for applications that require a
 persistent name service.  The Handle System provides the necessary
 mechanisms to allow persistent names to be registered as handles.

Sun, et al. Informational [Page 14] RFC 3650 Handle System Overview November 2003

 Specific naming authorities may be defined to host those handles
 designed to be persistent.  However, the persistence of handles
 depends more on administrative policies than the technology itself.
 Such policies are beyond the Handle System service, as described in
 this set of documents.
 On the other hand, the Handle System can also be used for
 applications where persistent names are not required.  Such handles
 may have a short life-time and they may also be used to identify
 different objects at different times.
 Different web applications may be developed using the Handle System
 as the underlying name service.  Each of these applications may
 define its own URI/URN namespace for its application needs.  For
 example, application FOO may have a URI namespace "foo:" registered
 to identify any FOO services on the web.  In the mean time,
 application BAR may have a URN namespace "URN:BAR" registered to
 identify any BAR object that needs a persistent name.  Both FOO and
 BAR applications may use handles (under their respective naming
 authority) in naming and resolving to services and/or objects.  This
 is similar in DNS, where there are different URI schemes (e.g.,
 "telnet", "ftp", "mailto", etc.) defined for different applications,
 all using the DNS service.
 The IETF and IRTF have discussed the Handle System in the realm of
 URI-related work.  There are different opinions on whether the Handle
 System will fit into a specific URI or URN namespace.  There are also
 concerns on where the Handle System fits in relation to other
 existing name services on the Internet.  Such discussions are out of
 the scope of this document.

7. Security Considerations

 This section is meant to inform people of security limitations of the
 Handle System, as well as precautions that should be taken by
 application developers, service providers, and Handle System clients.
 Specific security considerations regarding the Handle System protocol
 [21], as well as its data and service model [22], are addressed in
 separate documents.

7.1. General Security Practice

 The security of the Handle System depends on both client and server
 host security at every step in the transaction.  It assumes the
 client host has not been tampered with and that client software will
 reliably convey the received data to the client.  The client of any
 handle service must also assume that any handle servers involved have
 not been compromised.  To trust the Global Handle Registry is to

Sun, et al. Informational [Page 15] RFC 3650 Handle System Overview November 2003

 believe that the Global Handle Registry will correctly direct the
 client request to the responsible Local Handle Service.  To trust a
 Local Handle Service is to believe that the Local Handle Service will
 correctly return the data that was assigned to the handle by its
 administrator.  A Local Handle Service typically supports a set of
 naming authorities.  Thus, trusting a Local Handle Service would
 imply trusting those naming authorities.
 The integrity of the Handle System depends heavily on the integrity
 of the global service information.  Invalid global service
 information may mislead clients into inappropriate Local Handle
 Services.  It may also allow attackers to forge server signatures.
 The Global Handle Registry must take extreme caution in protecting
 the global service information and the public key pair used to sign
 the global service information.  Client applications should only
 accept the global service information from the Global Handle
 Registry.  They should check its integrity upon each update.
 For efficiency reasons, handle servers will not generate or return a
 digital signature for every service response, unless specifically
 requested by clients.  To assure data integrity, clients must
 explicitly ask the server to return the digital signature.  To
 protect sensitive data from exposure, clients may establish a
 communication session with the server and ask the server to encrypt
 any data using the session key.

7.2. Privacy Protection

 By default, most handle data stored in the Handle System is publicly
 accessible, unless otherwise specified by the handle administrator.
 Handle administrators must pay attention when adding handle values
 that contain private information.  They may choose to mark these
 handle values readable only by the handle administrator(s), or to
 store these as encrypted handle values, so that these values can only
 be read within a controlled audience.
 Log files generated by the handle server are another vulnerable point
 where client privacy may be under attack.  Operators of handle
 servers must protect such information carefully.

7.3. Caching and Proxy Servers

 Besides performance gains and other value-added services, both proxy
 and caching servers present themselves as men-in-the-middle, and as
 such are vulnerable to man-in-the-middle attacks.  It is important to
 know that proxy and caching servers are not part of any handle
 service.  They are clients of the Handle System.  Service responses
 from proxy and caching servers cannot be authenticated via the Handle

Sun, et al. Informational [Page 16] RFC 3650 Handle System Overview November 2003

 System protocol.  The trust between the client and its immediate
 proxy/caching server has to be setup independently, regardless of the
 number of proxy/caching servers that are in the middle of the
 communication path.
 By using proxy and caching servers, clients assume that the servers
 will submit their requests and relay any responses from the Handle
 System without mishandling any of the contents.  They also assume
 that the servers will protect any sensitive information on their
 behalf.
 Proxy and caching server operators should protect the systems on
 which such servers are running as they would protect any system that
 contains or transports sensitive information.  In particular, log
 information gathered at proxies often contain highly sensitive
 personal information, and/or information about organizations.  Such
 information should be carefully guarded, and appropriate guidelines
 for their use developed and followed.
 Caching servers provide additional potential vulnerabilities because
 the contents of the cache represent an attractive target for
 malicious exploitation.  Potential attacks on the cache can reveal
 private data for a handle user, or information still kept after a
 user believes that they have been removed from the network.
 Therefore, cache contents should be protected as sensitive
 information.

7.4. Mirroring

 Handle System clients should be aware of possible delays in content
 replication among mirroring sites.  They should consider sending
 their request to the primary service site for any time-sensitive
 data.  Selection of mirroring sites by service administrators must be
 done carefully.  Each mirroring site must follow the same security
 procedures in order to ensure data integrity.  Software tools may be
 applied to ensure data consistency among mirroring sites.

7.5. Denial of Service (DoS)

 As with any public service, the Handle System is subject to denial of
 service attacks.  No general solutions are available to protect
 against such attacks in today's technology.  Server implementations
 may be developed to be aware of such attacks and notify
 administrators when they happen.  Stateless cookies [19, 20] are one
 means of mitigating some of the effects of DoS attacks on hosts that
 perform authentication, integrity, and encryption services.  Server

Sun, et al. Informational [Page 17] RFC 3650 Handle System Overview November 2003

 implementations, moreover, need to be upgradeable to take advantage
 of new security technologies, including anti-DoS technologies as
 these become available.

8. History of the Handle System

 The Handle System was originally conceived and developed at CNRI as
 part of an overall digital object architecture.  The first public
 implementation was created at CNRI in the fall of 1994 in an effort
 led by David Ely.  The overall digital object architecture, including
 the Handle System, was later described in a paper by Robert Kahn and
 Robert Wilensky [1] in 1995.  Development continued at CNRI as part
 of the Computer Science Technical Reports (CSTR) project, funded by
 the Defense Advanced Projects Agency (DARPA) under Grant Number MDA-
 972-92-J-1029 and MDA-972-99-1-0018.  One aspect of this early
 digital library project, which was also a major factor in the
 evolution of the Networked Computer Science Technical Reference
 Library (NCSTRL) [18] and related activities, was to develop a
 framework for the underlying infrastructure of digital libraries.
 Early adopters of the Handle System included the Library of Congress,
 the Defense Technical Information Center (DTIC), and the
 International DOI Foundation (IDF).  Feedback from these
 organizations as well as NCSTRL, other digital library projects, and
 related IETF efforts as mentioned above, have all contributed to the
 evolution of the Handle System.  The current status and available
 software, for both client and server, can be found at
 http://www.handle.net.

9. Acknowledgements

 This work is derived from the earlier versions of the Handle System
 implementation.  Design ideas are based on those discussed within the
 Handle System development team, including David Ely, Charles Orth,
 Allison Yu, Sean Reilly, Jane Euler, Catherine Rey, Stephanie Nguyen,
 Jason Petrone, and Helen She.  Their contributions to this work are
 gratefully acknowledged.
 The authors also thank Russ Housley (housley@vigilsec.com), Ted
 Hardie (hardie@qualcomm.com), and Mark Baugher (mbaugher@cisco.com)
 for their extensive review and comments, as well as recommendations
 received from other members of the IETF/IRTF community.

Sun, et al. Informational [Page 18] RFC 3650 Handle System Overview November 2003

10. References and Bibliography

 [1]  Kahn, R. and R. Wilensky, "A Framework for Distributed Digital
      Object Services", D-Lib Magazine, 1995.
 [2]  Mockapetris, P., "Domain Names - Concepts and  Facilities", STD
      13, RFC 1034, November 1987.
 [3]  Mockapetris, P., "Domain Names - Implementation and
      Specification", STD 13, RFC 1035, November 1987.
 [4]  Berners-Lee, T., Masinter, L. and M. McCahill, "Uniform Resource
      Locators (URL)", RFC 1738, December 1994.
 [5]  Yergeau, F., "UTF-8, a transformation format of Unicode and ISO
      10646", RFC 2044, October 1996.
 [6]  ITU-T Rec. X.500, "The Directory: Overview of Concepts, Models,
      and Services", 1993.
 [7]  D. W. Chadwick, "Understanding X.500 - The Directory", Chapman &
      Hall ISBN: 0-412-43020-7.
 [8]  Wahl, M., Howes, T. and S. Kille, "Lightweight Directory Access
      Protocol (v3)", RFC 2251, December 1997.
 [9]  Sollins, K. and L. Masinter, "Functional Requirements for
      Uniform Resource Names", RFC 1737, December 1994.
 [10] Sollins, K. "Architectural Principles of Uniform Resource Name
      Resolution", RFC 2276, January 1998.
 [11] IETF Uniform Resource Names (URN) Working Group, April 1998.
 [12] D-Lib Magazine, http://www.dlib.org
 [13] Sam X. Sun, "Internationalization of the Handle System - A
      Persistent Global Name Service", Proceeding of 12th
      International Unicode Conference, April 1998.
 [14] D. Goodman, C. Robbins, "Understanding LDAP & X.500", August
      1997.
 [15] Deutsch P., Schoultz R., Faltstrom P. and C. Weider,
      "Architecture of the WHOIS++ service", RFC 1835, August 1995.
 [16] Weider, C., Fullton, J. and S. Spero, "Architecture of the
      Whois++ Index Service", RFC 1913, February 1996.

Sun, et al. Informational [Page 19] RFC 3650 Handle System Overview November 2003

 [17] The Unicode Consortium, "The Unicode Standard, Version v3.0",
      Addison-Wesley Pub Co; ISBN: 0201616335.
 [18] The Networked Computer Science Technical Reports Library
      (NCSTRL), http://www.ncstrl.org/
 [19] Karn, P. and W. Simpson, "Photuris: Session-Key Management
      Protocol", RFC 2522, March 1999.
 [20] Harkins, D. and D. Carrel, "The Internet Key Exchange (IKE)",
      RFC 2409, November 1998.
 [21] Sun, S., Reilly, S. and L. Lannom, "Handle System Namespace and
      Service Definition", RFC 3651, November 2003.
 [22] Sun, S., Reilly, S., Lannom, L. and J. Petrone, "Handle System
      Protocol (ver 2.1) Specification", RFC 3652, November 2003.
 [23] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform Resource
      Identifiers (URI): Generic Syntax", RFC 2396, August 1998.

11. Authors' Addresses

 Sam X. Sun
 Corporation for National Research Initiatives (CNRI)
 1895 Preston White Dr., Suite 100
 Reston, VA 20191
 Phone: 703-262-5316
 EMail: ssun@cnri.reston.va.us
 Larry Lannom
 Corporation for National Research Initiatives (CNRI)
 1895 Preston White Dr., Suite 100
 Reston, VA 20191
 Phone: 703-620-8990
 EMail: llannom@cnri.reston.va.us
 Brian Boesch
 Corporation for National Research Initiatives (CNRI)
 1895 Preston White Dr., Suite 100
 Reston, VA 20191
 Phone: 703-262-5316
 EMail: bboesch@cnri.reston.va.us

Sun, et al. Informational [Page 20] RFC 3650 Handle System Overview November 2003

12. Full Copyright Statement

 Copyright (C) The Internet Society (2003).  All Rights Reserved.
 This document and translations of it may be copied and furnished to
 others, and derivative works that comment on or otherwise explain it
 or assist in its implementation may be prepared, copied, published
 and distributed, in whole or in part, without restriction of any
 kind, provided that the above copyright notice and this paragraph are
 included on all such copies and derivative works.  However, this
 document itself may not be modified in any way, such as by removing
 the copyright notice or references to the Internet Society or other
 Internet organizations, except as needed for the purpose of
 developing Internet standards in which case the procedures for
 copyrights defined in the Internet Standards process must be
 followed, or as required to translate it into languages other than
 English.
 The limited permissions granted above are perpetual and will not be
 revoked by the Internet Society or its successors or assignees.
 This document and the information contained herein is provided on an
 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Sun, et al. Informational [Page 21]

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