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rfc:rfc9536



Internet Engineering Task Force (IETF) M. Loffredo Request for Comments: 9536 M. Martinelli Category: Standards Track IIT-CNR/Registro.it ISSN: 2070-1721 April 2024

      Registration Data Access Protocol (RDAP) Reverse Search

Abstract

 The Registration Data Access Protocol (RDAP) does not include query
 capabilities for finding the list of domains related to a set of
 entities matching a given search pattern.  Considering that an RDAP
 entity can be associated with any defined object class and other
 relationships between RDAP object classes exist, a reverse search can
 be applied to other use cases besides the classic domain-entity
 scenario.  This document describes an RDAP extension that allows
 servers to provide a reverse search feature based on the relationship
 defined in RDAP between an object class for search and any related
 object class.  The reverse search based on the domain-entity
 relationship is treated as a particular case.

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 7841.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 https://www.rfc-editor.org/info/rfc9536.

Copyright Notice

 Copyright (c) 2024 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (https://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Revised BSD License text as described in Section 4.e of the
 Trust Legal Provisions and are provided without warranty as described
 in the Revised BSD License.

Table of Contents

 1.  Introduction
   1.1.  Background
   1.2.  Conventions Used in This Document
 2.  Reverse Search Path Segment Specification
 3.  Reverse Search Definition
 4.  Reverse Search Properties Discovery
 5.  Reverse Search Properties Mapping
 6.  Reverse Search Response Specification
 7.  Reverse Search Query Processing
 8.  Reverse Searches Based on Entity Details
 9.  RDAP Conformance
 10. Implementation Considerations
 11. IANA Considerations
   11.1.  RDAP Extensions Registry
   11.2.  RDAP Reverse Search Registries
     11.2.1.  Creation of the RDAP Reverse Search Registries
     11.2.2.  Submit Requests to IANA
     11.2.3.  RDAP Reverse Search Registry
       11.2.3.1.  Template
       11.2.3.2.  Initial Content
     11.2.4.  RDAP Reverse Search Mapping Registry
       11.2.4.1.  Template
       11.2.4.2.  Initial Content
 12. Privacy Considerations
 13. Security Considerations
 14. References
   14.1.  Normative References
   14.2.  Informative References
 Appendix A.  Paradigms to Enforce Access Control on Reverse Search
         in RDAP
 Acknowledgements
 Authors' Addresses

1. Introduction

 The protocol described in this specification aims to extend the RDAP
 query capabilities and response to enable reverse search based on the
 relationships defined in RDAP between an object class for search and
 a related object class.  The reverse search based on the domain-
 entity relationship is treated as a particular case of such a generic
 model.
 RDAP providers willing to implement this specification should
 carefully consider its implications on the efficiency (see
 Section 10), the security (see Section 13), and the compliance with
 privacy regulations (see Section 12) of their RDAP service.

1.1. Background

 Reverse WHOIS is a service provided by many web applications that
 allows users to find domain names owned by an individual or a company
 starting from the owner's details, such as name and email.  Even if
 it has been considered useful for some legal purposes (e.g.,
 uncovering trademark infringements and detecting cybercrimes), its
 availability as a standardized WHOIS [RFC3912] capability has been
 objected to for two main reasons, which now don't seem to conflict
 with an RDAP implementation.
 The first objection concerns the potential risks of privacy
 violation.  However, the domain name community is considering a new
 generation of Registration Directory Services [ICANN-RDS] [ICANN-RA]
 that provide access to sensitive data under some permissible purposes
 and in accordance with appropriate policies for requestor
 accreditation, authentication, and authorization.  RDAP's reliance on
 HTTP means that it can make use of common HTTP-based approaches to
 authentication and authorization, making it more useful than WHOIS in
 the context of such directory services.  Since RDAP consequently
 permits a reverse search implementation complying with privacy
 protection principles, this first objection is not well-founded.
 The second objection to the implementation of a reverse search
 capability has been connected with its impact on server processing.
 However, the core RDAP specifications already define search queries,
 with similar processing requirements, so the basis of this objection
 is not clear.
 Reverse searches, such as finding the list of domain names associated
 with contacts or nameservers, may be useful to registrars as well.
 Usually, registries adopt out-of-band solutions to provide results to
 registrars asking for reverse searches on their domains.  Possible
 reasons for such requests are:
  • the loss of synchronization between the registrar database and the

registry database and

  • the need for such data to perform bulk Extensible Provisioning

Protocol (EPP) [RFC5730] updates (e.g., changing the contacts of a

    set of domains, etc.).
 Currently, RDAP does not provide any means for a client to search for
 the collection of domains associated with an entity [RFC9082].  A
 query (lookup or search) on domains can return the array of entities
 related to a domain with different roles (registrant, registrar,
 administrative, technical, reseller, etc.), but the reverse operation
 is not allowed.  Only reverse searches to find the collection of
 domains related to a nameserver (ldhName or ip) can be requested.
 Since an entity can be in relationship with any RDAP object
 [RFC9083], the availability of a reverse search as largely intended
 can be common to all the object classes allowed for search.  Through
 a further step of generalization, the meaning of reverse search in
 the RDAP context can be extended to include any query for retrieving
 all the objects that relates to another query matching a given search
 pattern.

1.2. Conventions Used in This Document

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
 "OPTIONAL" in this document are to be interpreted as described in
 BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
 capitals, as shown here.

2. Reverse Search Path Segment Specification

 A generic reverse search path is described by the syntax:
 {searchable-resource-type}/reverse_search/{related-resource-
 type}?<search-condition>
 The path segments are defined as follows:
 "searchable-resource-type":  It MUST be one of the resource types for
    search defined in Section 3.2 of [RFC9082] (i.e., "domains",
    "nameservers", and "entities") or a resource type extension.
 "related-resource-type":  It MUST be one of the resource types for
    lookup defined in Section 3.1 of [RFC9082] (i.e., "domain",
    "nameserver", "entity", "ip", and "autnum") or a resource type
    extension.
 "search-condition":  A sequence of "property=search pattern"
    predicates separated by the ampersand character ('&', US-ASCII
    value 0x0026).
 While related-resource-type is defined as having one of a number of
 different values, the only reverse searches defined in this document
 are for a related-resource-type of "entity".  Reverse searches for
 the other resource types specified in [RFC9082] and resource type
 extensions may be defined by future documents.

3. Reverse Search Definition

 Based on the content of Section 2, defining a reverse search means to
 define the triple <searchable resource type, related resource type,
 property> and the mapping with the corresponding RDAP object member.
 The mapping is done through the use of a JSONPath expression
 [RFC9535].  Reverse searches are registered in the "RDAP Reverse
 Search" registry (see Section 11.2.3), whereas reverse search
 mappings are registered in the "RDAP Reverse Search Mapping" registry
 (see Section 11.2.4).  The reason for having two registries is that
 it may be possible for a single type of reverse search to rely on
 different members, depending on the server's configuration (see
 Section 5).
 All of the reverse searches defined by this document (see Section 8)
 have property names that are the same as the name of the RDAP object
 member that is the subject of the search.  For example, the reverse
 search with the property name "fn" relies on the value of the "fn"
 member inside the jCard of an entity object.  However, it is not
 necessary that these two names be the same.  In particular, remapping
 of searches as part of the deprecation of an existing member (see
 Section 5) will typically lead to a member with a different name
 being used for the search.
 Servers MUST NOT provide or implement reverse searches or reverse
 search mappings that are not registered with IANA.

4. Reverse Search Properties Discovery

 Servers complying with this specification MUST extend the help
 response [RFC9083] with the "reverse_search_properties" member that
 contains an array of objects with the following mandatory child
 members:
 "searchableResourceType":  the searchable resource type of the
    reverse search query, as defined in Section 2
 "relatedResourceType":  the related resource type of the reverse
    search query, as defined in Section 2
 "property":  the reverse search property used in the predicate of the
    reverse search query, as defined in Section 2
 An example of the help response including the
 "reverse_search_properties" member is shown in Figure 2

5. Reverse Search Properties Mapping

 To permit clients to determine the member used by the server for a
 reverse search, servers MUST detail the mapping that is occurring by
 adding the "reverse_search_properties_mapping" member to the topmost
 object of a reverse search response.  This data structure is included
 in the search response, rather than in the help response, because it
 may differ depending on the query that is sent to the server.
 Documents that deprecate or restructure RDAP responses such that a
 registered reverse search is no longer able to be used MUST either
 note that the relevant reverse search is no longer available (in the
 case of deprecation) or describe how to continue supporting the
 relevant search by adding another mapping for the reverse search
 property (in the case of restructuring).
 The "reverse_search_properties_mapping" member contains an array of
 objects with the following mandatory child members:
 "property":  the reverse search property used in the predicate of the
    current query, as defined in Section 2
 "propertyPath":  the JSONPath expression of the object member (or
    members) corresponding to the reverse search property
 The searchable and the related resource types are derived from the
 query, so there is no need to include them in addition to the
 property in this member.
 This member MUST be included for all properties used in the search,
 regardless of whether that property has multiple registered mappings
 as at the time of the search, because new mappings may be registered
 at any time.
 When applied to an object, the JSONPath expression MUST produce a
 list of values, each of which is a JSON number or string.
 An example of a reverse search response including the
 "reverse_search_properties_mapping" member is shown in Figure 3.

6. Reverse Search Response Specification

 Reverse search responses use the formats defined in Section 8 of
 [RFC9083], which correspond to the searchable resource types defined
 in Section 2.

7. Reverse Search Query Processing

 To process a reverse search, the server returns the objects from its
 data store that are of type searchable-resource-type and that match
 each of the predicates from the search conditions.  To determine
 whether an object matches a predicate, the server:
  • applies the mapping it uses for the reverse search property to the

object in order to generate a list of values, each of which MUST

    be a JSON number or string and
  • checks whether the search pattern matches one or more of those

values.

 A search pattern matches a value where it equals the string
 representation of the value or where it is a match for the value in
 accordance with the partial string matching behavior defined in
 Section 4.1 of [RFC9082].
 Objects are only included in the search results if they satisfy all
 included predicates.  This includes predicates that are for the same
 property; in such a case, it is necessary for the related object to
 match against each of those predicates.
 Servers MUST return an HTTP 501 (Not Implemented) [RFC9110] response
 to inform clients of unsupported reverse searches.
 Based on their policy, servers MAY restrict how predicates are used
 to make a valid search condition by returning a 400 (Bad Request)
 response when a problematic request is received.
 A given reverse search or reverse search mapping MAY define
 additional or alternative search behavior past that set out in this
 section.

8. Reverse Searches Based on Entity Details

 Since an entity can be associated with any other object class in
 RDAP, the most common kind of reverse search is one based on an
 entity's details.  Such reverse searches arise from the query model
 by setting the related resource type to "entity".
 By selecting a specific searchable resource type, the resulting
 reverse search aims at retrieving all the objects (e.g., all the
 domains) that are related to any entity object matching the search
 conditions.
 This section defines the reverse search properties servers SHOULD
 support for the domain, nameserver, entity-searchable resource types,
 and entity-related resource type:
 Reverse search property:  role
 RDAP member path:  $.entities[*].roles
 Reference:  Section 10.2.4 of [RFC9083]
 Reverse search property:  handle
 RDAP member path:  $.entities[*].handle
 Reference:  Section 5.1 of [RFC9083]
 Reverse search property:  fn
 RDAP member path:  $.entities[*].vcardArray[1][?(@[0]=='fn')][3]
 Reference:  Section 6.2.1 of [RFC6350]
 Reverse search property:  email
 RDAP member path:  $.entities[*].vcardArray[1][?(@[0]=='email')][3]
 Reference:  Section 6.4.2 of [RFC6350]
 The presence of a predicate on the reverse search property "role"
 means that the RDAP response property "roles" MUST contain at least
 the specified role.
 The last two properties are related to jCard elements [RFC7095], but
 the field references are to vCard [RFC6350], since jCard is the JSON
 format for vCard.
 Examples of reverse search paths based on the domain-entity
 relationship are presented in Figure 1.
  /domains/reverse_search/entity?handle=CID-40*&role=technical
  /domains/reverse_search/entity?fn=Bobby*&role=registrant
  /domains/reverse_search/entity?handle=RegistrarX&role=registrar
              Figure 1: Examples of Reverse Search Queries
 An example of the help response including the supported reverse
 search properties is shown in Figure 2.
    {
      "rdapConformance": [
        "rdap_level_0",
        "reverse_search"
      ],
      ...
      "reverse_search_properties": [
        {
          "searchableResourceType": "domains",
          "relatedResourceType": "entity",
          "property": "fn"
        },
        {
          "searchableResourceType": "domains",
          "relatedResourceType": "entity",
          "property": "handle"
        },
        {
          "searchableResourceType": "domains",
          "relatedResourceType": "entity",
          "property": "email"
        },
        {
          "searchableResourceType": "domains",
          "relatedResourceType": "entity",
          "property": "role"
        }
      ],
      ...
    }
        Figure 2: An Example of the Help Response including the
                   "reverse_search_properties" Member
 An example of a response including the mapping that is occurring for
 the first reverse search in Figure 1 is shown below.
    {
      "rdapConformance": [
        "rdap_level_0",
        "reverse_search"
      ],
      ...
      "reverse_search_properties_mapping": [
        {
          "property": "handle",
          "propertyPath": "$.entities[*].handle"
        },
        {
          "property": "role",
          "propertyPath": "$.entities[*].roles"
        }
      ],
      ...
    }
         Figure 3: An Example of an RDAP Response including the
               "reverse_search_properties_mapping" Member

9. RDAP Conformance

 Servers complying with this specification MUST include the value
 "reverse_search" in the rdapConformance property of the help response
 [RFC9083] and any other response including the
 "reverse_search_properties_mapping" member.  The information needed
 to register this value in the "RDAP Extensions" registry is described
 in Section 11.1.

10. Implementation Considerations

 To limit the impact of processing the search predicates, servers are
 RECOMMENDED to make use of techniques to speed up the data retrieval
 in their underlying data store, such as indexes or similar.  In
 addition, risks with respect to performance degradation or result set
 generation can be mitigated by adopting practices used for standard
 searches, e.g., restricting the search functionality, limiting the
 rate of search requests according to the user's authorization,
 truncating and paging the results [RFC8977], and returning partial
 responses [RFC8982].

11. IANA Considerations

11.1. RDAP Extensions Registry

 IANA has registered the following value in the "RDAP Extensions"
 registry:
 Extension Identifier:  reverse_search
 Registry Operator:  Any
 Specification:  RFC 9536
 Contact:  IETF <iesg@ietf.org>
 Intended Usage:  This extension identifier is used for both URI path
    segments and response extensions related to the reverse search in
    RDAP.

11.2. RDAP Reverse Search Registries

11.2.1. Creation of the RDAP Reverse Search Registries

 IANA has created the "RDAP Reverse Search" and "RDAP Reverse Search
 Mapping" registries within the "Registration Data Access Protocol
 (RDAP)" category in the protocol registries.
 These registries follow the Specification Required registration
 policy, as defined in Section 4.6 of [RFC8126].
 The designated expert should prevent collisions and confirm that
 suitable documentation, as described in Section 4.5 of [RFC8126], is
 available to ensure interoperability.
 Creators of either new RDAP reverse searches or new mappings for
 registered reverse searches SHOULD NOT replicate functionality
 already available by way of other documents referenced in these
 registries.  Creators MAY register additional reverse search mappings
 for existing properties, but they SHOULD NOT map a registered reverse
 search property to a response field with a meaning other than that of
 the response fields referenced by the mappings already registered for
 that property.  In other words, all the mappings for a reverse search
 property MUST point to response fields with the same meaning.

11.2.2. Submit Requests to IANA

 Registration requests can be sent to <iana@iana.org>.

11.2.3. RDAP Reverse Search Registry

11.2.3.1. Template

 Property:  The name of the reverse search property.
 Description:  A brief human-readable text describing the reverse
    search property.
 Searchable Resource Type:  The searchable resource type of the
    reverse search query (Section 2) including the reverse search
    property.  Multiple reverse search properties differing only by
    this field can be grouped together by listing all the searchable
    resource types separated by comma (see Section 11.2.3.2).
 Related Resource Type:  The related resource type of the reverse
    search query (Section 2) including the reverse search property.
 Registrant:  The name of the person registering the reverse search
    property.
 Contact Information:  An email address, postal address, or some other
    information to be used to contact the registrant.
 Reference:  Document (e.g., the RFC number) and section reference
    where the reverse search property is specified.
 The combination of Searchable Resource Type, Related Resource Type,
 and Property MUST be unique across the registry entries.

11.2.3.2. Initial Content

 IANA has registered the following entries in the "RDAP Reverse
 Search" registry.  For all entries, the common values are shown in
 Table 1, whereas the specific values are shown in Table 2.
     +==========================+================================+
     | Registry Property        | Value                          |
     +==========================+================================+
     | Searchable Resource Type | domains, nameservers, entities |
     +--------------------------+--------------------------------+
     | Related Resource Type    | entity                         |
     +--------------------------+--------------------------------+
     | Registrant               | IETF                           |
     +--------------------------+--------------------------------+
     | Contact Information      | iesg@ietf.org                  |
     +--------------------------+--------------------------------+
     | Reference                | RFC 9536                       |
     +--------------------------+--------------------------------+
           Table 1: Common Values for All Entries in the RDAP
                        Reverse Search Registry
      +==========+==============================================+
      | Property | Description                                  |
      +==========+==============================================+
      | fn       | The server supports the domain/nameserver/   |
      |          | entity search based on the full name (a.k.a. |
      |          | formatted name) of an associated entity      |
      +----------+----------------------------------------------+
      | handle   | The server supports the domain/nameserver/   |
      |          | entity search based on the handle of an      |
      |          | associated entity                            |
      +----------+----------------------------------------------+
      | email    | The server supports the domain/nameserver/   |
      |          | entity search based on the email address of  |
      |          | an associated entity                         |
      +----------+----------------------------------------------+
      | role     | The server supports the domain/nameserver/   |
      |          | entity search based on the role of an        |
      |          | associated entity                            |
      +----------+----------------------------------------------+
            Table 2: Specific Values for Entries in the RDAP
                        Reverse Search Registry

11.2.4. RDAP Reverse Search Mapping Registry

11.2.4.1. Template

 Property:  The same as defined in the "RDAP Reverse Search" registry.
 Property Path:  The JSONPath of the RDAP property this reverse search
    property maps to.
 Searchable Resource Type:  The same as defined in the "RDAP Reverse
    Search" registry.
 Related Resource Type:  The same as defined in the "RDAP Reverse
    Search" registry.
 Registrant:  The name of the person registering this reverse search
    property mapping.
 Contact Information:  The same as defined in the "RDAP Reverse
    Search" registry.
 Reference:  Document (e.g., the RFC number) and section reference
    where this reverse search property mapping is specified.
 The combination of Searchable Resource Type, Related Resource Type,
 Property, and Property Path MUST be unique across the registry
 entries.

11.2.4.2. Initial Content

 IANA has registered the following entries in the "RDAP Reverse Search
 Mapping" registry.  For all entries, the common values are the same
 as defined in the "RDAP Reverse Search" registry (see Table 1),
 whereas the specific values are shown below (see Table 3).
    +==========+==================================================+
    | Property | Property Path                                    |
    +==========+==================================================+
    | fn       | $.entities[*].vcardArray[1][?(@[0]=='fn')][3]    |
    +----------+--------------------------------------------------+
    | handle   | $.entities[*].handle                             |
    +----------+--------------------------------------------------+
    | email    | $.entities[*].vcardArray[1][?(@[0]=='email')][3] |
    +----------+--------------------------------------------------+
    | role     | $.entities[*].roles                              |
    +----------+--------------------------------------------------+
        Table 3: Specific Values for Entries in the RDAP Reverse
                        Search Mapping Registry

12. Privacy Considerations

 The search functionality defined in this document may affect the
 privacy of entities in the registry (and elsewhere) in various ways;
 see [RFC6973] for a general treatment of privacy in protocol
 specifications.  Registry operators should be aware of the trade-offs
 that result from implementing this functionality.
 Many jurisdictions have laws or regulations that restrict the use of
 "personal data", per the definition in [RFC6973].  Given that,
 registry operators should ascertain whether the regulatory
 environment in which they operate permits implementation of the
 functionality defined in this document.
 In those cases where this functionality makes use of sensitive
 information, the information MUST only be accessible to authorized
 users under a lawful basis.
 Since reverse search requests and responses could contain Personally
 Identifiable Information (PII), reverse search functionality MUST be
 available over HTTPS only.
 Providing reverse search in RDAP carries the following threats as
 described in [RFC6973]:
  • Correlation
  • Disclosure
  • Misuse of data
 Therefore, RDAP providers need to mitigate the risk of those threats
 by implementing appropriate measures supported by security services
 (see Section 13).

13. Security Considerations

 Security services that are required to provide controlled access to
 the operations specified in this document are described in [RFC7481].
 A non-exhaustive list of access control paradigms an RDAP provider
 can implement is presented in Appendix A.
 As an additional measure to enforce security by preventing reverse
 searches to be accessed from unauthorized users, the RDAP providers
 may consider physically separating the reverse search endpoints from
 the other ones by configuring a proxy routing the reverse searches to
 a dedicated backend server and leveraging further security services
 offered by other protocol layers, such as digital certificates and IP
 allow-listing.
 Finally, the specification of the relationship within the reverse
 search path allows the RDAP servers to implement different
 authorization policies on a per-relationship basis.

14. References

14.1. Normative References

 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119,
            DOI 10.17487/RFC2119, March 1997,
            <https://www.rfc-editor.org/info/rfc2119>.
 [RFC6350]  Perreault, S., "vCard Format Specification", RFC 6350,
            DOI 10.17487/RFC6350, August 2011,
            <https://www.rfc-editor.org/info/rfc6350>.
 [RFC7095]  Kewisch, P., "jCard: The JSON Format for vCard", RFC 7095,
            DOI 10.17487/RFC7095, January 2014,
            <https://www.rfc-editor.org/info/rfc7095>.
 [RFC7481]  Hollenbeck, S. and N. Kong, "Security Services for the
            Registration Data Access Protocol (RDAP)", STD 95,
            RFC 7481, DOI 10.17487/RFC7481, March 2015,
            <https://www.rfc-editor.org/info/rfc7481>.
 [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
            Writing an IANA Considerations Section in RFCs", BCP 26,
            RFC 8126, DOI 10.17487/RFC8126, June 2017,
            <https://www.rfc-editor.org/info/rfc8126>.
 [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
            2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
            May 2017, <https://www.rfc-editor.org/info/rfc8174>.
 [RFC9082]  Hollenbeck, S. and A. Newton, "Registration Data Access
            Protocol (RDAP) Query Format", STD 95, RFC 9082,
            DOI 10.17487/RFC9082, June 2021,
            <https://www.rfc-editor.org/info/rfc9082>.
 [RFC9083]  Hollenbeck, S. and A. Newton, "JSON Responses for the
            Registration Data Access Protocol (RDAP)", STD 95,
            RFC 9083, DOI 10.17487/RFC9083, June 2021,
            <https://www.rfc-editor.org/info/rfc9083>.
 [RFC9110]  Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
            Ed., "HTTP Semantics", STD 97, RFC 9110,
            DOI 10.17487/RFC9110, June 2022,
            <https://www.rfc-editor.org/info/rfc9110>.
 [RFC9535]  Gössner, S., Ed., Normington, G., Ed., and C. Bormann,
            Ed., "JSONPath: Query Expressions for JSON", RFC 9535,
            DOI 10.17487/RFC9535, February 2024,
            <https://www.rfc-editor.org/info/rfc9535>.

14.2. Informative References

 [ICANN-RA] ICANN, "Base Registry Agreement", January 2024,
            <https://www.icann.org/en/registry-agreements/base-
            agreement>.
 [ICANN-RDS]
            ICANN, "Final Report from the Expert Working Group on gTLD
            Directory Services: A Next-Generation Registration
            Directory Service (RDS)", June 2014,
            <https://www.icann.org/en/system/files/files/final-report-
            06jun14-en.pdf>.
 [OIDCC]    Sakimura, N., Bradley, J., Jones, M., de Medeiros, B., and
            C. Mortimore, "OpenID Connect Core 1.0 incorporating
            errata set 2", December 2023,
            <http://openid.net/specs/openid-connect-core-1_0.html>.
 [RFC3912]  Daigle, L., "WHOIS Protocol Specification", RFC 3912,
            DOI 10.17487/RFC3912, September 2004,
            <https://www.rfc-editor.org/info/rfc3912>.
 [RFC5730]  Hollenbeck, S., "Extensible Provisioning Protocol (EPP)",
            STD 69, RFC 5730, DOI 10.17487/RFC5730, August 2009,
            <https://www.rfc-editor.org/info/rfc5730>.
 [RFC6973]  Cooper, A., Tschofenig, H., Aboba, B., Peterson, J.,
            Morris, J., Hansen, M., and R. Smith, "Privacy
            Considerations for Internet Protocols", RFC 6973,
            DOI 10.17487/RFC6973, July 2013,
            <https://www.rfc-editor.org/info/rfc6973>.
 [RFC8977]  Loffredo, M., Martinelli, M., and S. Hollenbeck,
            "Registration Data Access Protocol (RDAP) Query Parameters
            for Result Sorting and Paging", RFC 8977,
            DOI 10.17487/RFC8977, January 2021,
            <https://www.rfc-editor.org/info/rfc8977>.
 [RFC8982]  Loffredo, M. and M. Martinelli, "Registration Data Access
            Protocol (RDAP) Partial Response", RFC 8982,
            DOI 10.17487/RFC8982, February 2021,
            <https://www.rfc-editor.org/info/rfc8982>.

Appendix A. Paradigms to Enforce Access Control on Reverse Search in

           RDAP
 Access control can be implemented according to different paradigms
 introducing increasingly stringent rules.  The paradigms listed below
 leverage the capabilities that are either built in or provided as
 extensions by the OpenID Connect [OIDCC]:
 Role-Based Access Control (RBAC):  Access rights are granted
    depending on roles.  Generally, this is done by grouping users
    into fixed categories and assigning static grants to each
    category.  A more dynamic approach can be implemented by using the
    OpenID Connect "scope" claim.
 Purpose-Based Access Control (PBAC):  Access rules are based on the
    notion of purpose, being the intended use of some data by a user.
    It can be implemented by tagging a request with the usage purpose
    and making the RDAP server check the compliance between the given
    purpose and the control rules applied to the data to be returned.
 Attribute-Based Access Control (ABAC):  Rules to manage access rights
    are evaluated and applied according to specific attributes
    describing the context within which data are requested.  It can be
    implemented within an out-of-band process by setting additional
    OpenID Connect claims that describe the request context and make
    the RDAP server check for compliance between the given context and
    the control rules that are applied to the data to be returned.
 Time-Based Access Control (TBAC):  Data access is allowed for a
    limited time only.  It can be implemented by assigning users
    temporary credentials linked to access grants with limited scopes.
 With regard to the privacy threats reported in Section 12,
 correlation and disclosure can be mitigated by minimizing both the
 request features and the response data based on user roles (i.e.,
 RBAC).  Misuse can be mitigated by checking for the purpose of the
 request (i.e., PBAC).  It can be accomplished according to the
 following approaches:
 Full Trust:  The registry trusts the fairness of an accredited user.
    The requestor is always legitimized to submit their requests under
    a lawful basis.  Additionally, they can be required to specify the
    purpose as either a claim of their account or a query parameter.
    In the former case, the purpose is assumed to be the same for
    every request.  In the latter case, the purpose must be one of
    those associated to the user.
 Zero Trust:  The registry requires documents that assess whether the
    requestor is legitimized to submit a given request.  It can be
    implemented by assigning the requestor a temporary OpenID account
    linked to the given request (i.e., TBAC) and describing the
    request through a set of claims (i.e., ABAC).  The association
    between the temporary account and the claims about the request is
    made by an out-of-band application.  In so doing, the RDAP server
    is able to check that the incoming request is consistent with the
    request claims linked to the temporary account.
 The two approaches can be used together:
  • The former is suitable for users carrying out a task in the public

interest or exercising their official authority (e.g., an officer

    of a cybercrime agency).  Similarly, registrars can submit reverse
    searches on their domains and contacts based on their contractual
    relationship with the domain holders.  In this case, the query
    results can be restricted to those pertaining to a registrar by
    adding an implicit predicate to the search condition.
  • The latter can be taken to allow domain name dispute resolution

service providers to request information in defense of the

    legitimate interests of complainants.

Acknowledgements

 The authors would like to acknowledge the following individuals for
 their contributions to this document: Francesco Donini, Scott
 Hollenbeck, Francisco Arias, Gustavo Lozano, Eduardo Alvarez, Ulrich
 Wisser, James Gould, and Pawel Kowalik.
 Tom Harrison and Jasdip Singh provided relevant feedback and constant
 support to the implementation of this proposal.  Their contributions
 have been greatly appreciated.

Authors' Addresses

 Mario Loffredo
 IIT-CNR/Registro.it
 Via Moruzzi,1
 56124 Pisa
 Italy
 Email: mario.loffredo@iit.cnr.it
 URI:   http://www.iit.cnr.it
 Maurizio Martinelli
 IIT-CNR/Registro.it
 Via Moruzzi,1
 56124 Pisa
 Italy
 Email: maurizio.martinelli@iit.cnr.it
 URI:   http://www.iit.cnr.it
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