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Handle System Overview

The information below is for an old version of the document that is already published as an RFC.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 3650.
Authors Larry Lannom , Lt. Col. Brian P. Boesch , Sam Sun
Last updated 2020-01-21 (Latest revision 2003-07-23)
RFC stream Independent Submission
Stream ISE state (None)
Consensus boilerplate Unknown
Document shepherd (None)
IESG IESG state RFC 3650 (Informational)
Telechat date (None)
Responsible AD Ted Hardie
IESG note It is suggested that these go forward with the following
IESG Note attached (originally drafted by Patrik): IESG NOTE: The IETF and IRTF have discussed the Handle system in the realm
of URI-related work. The IESG wishes to point out that there
is no IETF consensus on the current Handle system nor on
where it fits in the IETF architecture. The IESG is of the view that
the Handle system would be able to, with very small changes,
fit into the IETF architecture as a URN namespace. These documents,
however, contain information on the Handle system without these changes.
Send notices to (None)
Internet Draft                                              Sam X. Sun 
 Document: draft-sun-handle-system-12.txt                          CNRI 
 Expires: January 2003                                     Larry Lannom 
                                                           Brian Boesch 
                                                              July 2003 
                           Handle System Overview 
 Status of this Memo  
    This document is an Internet-Draft and is in full conformance with 
    all provisions of Section 10 of RFC2026.  
    Internet-Drafts are working documents of the Internet Engineering 
    Task Force (IETF), its areas, and its working groups.  Note that 
    other groups may also distribute working documents as Internet-
    Internet-Drafts are draft documents valid for a maximum of six 
    months and may be updated, replaced, or obsoleted by other 
    documents at any time. It is inappropriate to use Internet-Drafts 
    as reference material or to cite them other than as "work in 
    The list of current Internet-Drafts can be accessed at    
    The list of Internet-Draft Shadow Directories can be accessed at    
    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 URN. 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.  
 Table of Contents 
    1. Introduction..................................................2 
    2. Motivations...................................................5 
    3. Handle Namespace..............................................6 
    4. Handle System Architecture....................................8 
    5. Handle System Security.......................................11 
    6. The Handle System and other Internet Services................12 
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    6.1 Domain Name Service (DNS)...................................12 
    6.2 Directory Services (X.500/LDAP).............................13 
    6.3 Uniform Resource Identifier (URI)/Uniform Resource Name(URN) 13 
    7. Security Considerations......................................14 
    7.1 General Security Practice...................................15 
    7.2 Privacy Protection..........................................15 
    7.3 Caching and Proxy Servers...................................16 
    7.4 Mirroring...................................................16 
    7.5 Denial of Service (DoS).....................................17 
    8. History of the Handle System.................................17 
    9. Acknowledgements.............................................17 
    References and Bibliography.....................................18 
    Author's Addresses..............................................19 
 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) remain intact after joining the Handle 
    System. Any handle request to the local namespace may be processed 
    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 that are in use 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 
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    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 one or 
    more 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 
    DNS name and 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 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: 
       . Uniqueness: Every handle is globally unique within the Handle 

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       . Persistence: Handles may be used as persistent identifiers for 
         Internet resources. A handle does not have to be derived in 
         any way 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. 
       . 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 
       . Multiple Attributes: A single handle can refer to multiple 
         attributes of a resource, including associated services, 
         available through any method, again 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.  
       . 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.  
       . 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.  
       . Distributed Service Model: The Handle System defines a 
         hierarchical service model such that any local handle 
         namespace may be serviced either by a corresponding local 
         handle service or 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 
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         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.) 
       . 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.  
       . 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. 
       . 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 
    can be found under the Handle System website at 
 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 take either an abstract services 
    approach (e.g., URI/URN) or an approach to name resolution absent a 
    self-contained framework for reliable yet distributed 

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    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 update 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 the 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 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.  
 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 
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    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 presents 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 is 
    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 
    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 
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    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 
    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. 
    Neither are there any limits on the number of servers that make up 
    each site. Replication among any service sites 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, 
    to accommodate any large-scale of operation, and to mitigate 
    problems of single point failure.  
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    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. 
        -------------------------              ------------------  
       |  ---------   ---------  |            |  -----    -----  | 
       | |         | |         | |            | |  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) 
        Fig. 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 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 
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    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 
      |                        |    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    |                   |                      | 
           |               |                    ---------------------- 
               Fig. 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.    
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 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. 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 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 
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    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.     
 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. RFC1034 [2] and RFC1035 [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 
    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 

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    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 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 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 
    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 from 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 
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    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. 
    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 
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    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 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 handle values encrypted, so 
    that these values can only be readable within a controlled  
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    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 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 
    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 
 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 

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    tools may be applied to ensure data consistency among mirroring 
 7.5 Denial of Service (DoS) 
    As with any public service, the Handle System is subject to denial 
    of service attack. 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 to mitigate some of the effects of DoS attacks on hosts that 
    perform authentication, integrity, and encryption services. Server 
    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. 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. Current status and available 
    software, both client and server, can be found at 
 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. 
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    The authors also thank Russ Housley (, Ted 
    Hardie (, and Mark Baugher ( 
    for their extensive review and comments, as well as recommendations 
    received from other members of the IETF/IRTF community. 
 References and Bibliography 
    [1] R. Kahn, & R. Wilensky, "A Framework for Distributed Digital 
    Object Services", D-Lib Magazine, 1995 
    RFC1034, November 1987 
    SPECIFICATION", RFC1035, November 1987 
    [4] Berners-Lee, T., Masinter, L., McCahill, M., et al., "Uniform 
    Resource Locators (URL)", RFC1738, December 1994 
    [5] Yergeau, Francois, "UTF-8, A Transform Format for Unicode and 
    ISO10646", RFC2044, 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, 
    [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 
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    [15] Deutsch P., Schoultz R., Faltstrom P., and C. Weider, 
    "Architecture of the Whois++ service", RFC 1835, August 1995 
    [16] Weider, C., J. Fullton, and S. Spero, "Architecture of the 
    Whois++ Index Service", RFC 1913, February 1996 
    [17] The Unicode Consortium, "The Unicode Standard, Version v3.0", 
    Addison-Wesley Pub Co; ISBN: 0201616335 
    [18] The Networked Computer Science Technical Reports Library 
    [19] P. Karn, W. Simpson, "Photuris: Session-Key Management 
    Protocol", March, 1999 
    [20] D. Harkins, D Carrel, "The Internet Key Exchange (IKE)", 
    November, 1998 
    [21] S. Sun, S. Reilly, L. Lannom, "Handle System Namespace and 
    Service Definition", IETF draft,
    drafts/draft-sun-handle-system-def-08.txt, work in progress         
    [22] S. Sun, S. Reilly, L. Lannom, J. Petrone, "Handle System 
    Protocol Specification", IETF draft,
    drafts/draft-sun-handle-system-protocol-05.txt, work in progress 
    [23] T. Berners-Lee, R. Fielding, L. Masinter, "Uniform Resource 
    Identifiers (URI): Generic Syntax", RFC 2396, August 1998 
 Author's Addresses  
    Sam X. Sun 
    Corporation for National Research Initiatives (CNRI) 
    1895 Preston White Dr.  Suite 100 
    Reston, VA 20191  
    Phone: 703-262-5316 
    Larry Lannom 
    Corporation for National Research Initiatives (CNRI) 
    1895 Preston White Dr.     Suite 100 
    Reston, VA 20191 
    Phone: 703-620-8990 
    Brian Boesch 
    Corporation for National Research Initiatives (CNRI) 
    1895 Preston White Dr.  Suite 100 
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    Reston, VA 20191  
    Phone: 703-262-5316 

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