Registration Data Access Protocol (RDAP) Reverse search capabilities
draft-ietf-regext-rdap-reverse-search-18

Registration Protocols Extensions                            M. Loffredo
Internet-Draft                                             M. Martinelli
Intended status: Standards Track                     IIT-CNR/Registro.it
Expires: 27 August 2023                                 23 February 2023

  Registration Data Access Protocol (RDAP) Reverse search capabilities
                draft-ietf-regext-rdap-reverse-search-18

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 Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   Internet-Drafts are draft documents valid for a maximum of six months
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 27 August 2023.

Copyright Notice

   Copyright (c) 2023 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.

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   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  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Conventions Used in This Document . . . . . . . . . . . .   4
   2.  Reverse Search Path Segment Specification . . . . . . . . . .   4
   3.  Reverse Search Response Specification . . . . . . . . . . . .   5
   4.  Reverse Search Definition . . . . . . . . . . . . . . . . . .   5
   5.  Reverse Search Properties Discovery . . . . . . . . . . . . .   6
   6.  Reverse Search Properties Mapping . . . . . . . . . . . . . .   6
   7.  Reverse Searches Based on Entity Details  . . . . . . . . . .   7
   8.  RDAP Conformance  . . . . . . . . . . . . . . . . . . . . . .  10
   9.  Implementation Considerations . . . . . . . . . . . . . . . .  10
   10. Implementation Status . . . . . . . . . . . . . . . . . . . .  10
     10.1.  IIT-CNR/Registro.it RDAP Server  . . . . . . . . . . . .  11
     10.2.  IIT-CNR/Registro.it RDAP Client  . . . . . . . . . . . .  11
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12
     11.1.  RDAP Extensions Registry . . . . . . . . . . . . . . . .  12
     11.2.  RDAP Reverse Search Registries . . . . . . . . . . . . .  12
       11.2.1.  Creation of the RDAP Reverse Search Registries . . .  12
       11.2.2.  Submit Request to IANA . . . . . . . . . . . . . . .  12
       11.2.3.  RDAP Reverse Search Registry . . . . . . . . . . . .  12
         11.2.3.1.  Template . . . . . . . . . . . . . . . . . . . .  12
         11.2.3.2.  Initial Content  . . . . . . . . . . . . . . . .  13
       11.2.4.  RDAP Reverse Search Mapping Registry . . . . . . . .  14
         11.2.4.1.  Template . . . . . . . . . . . . . . . . . . . .  14
         11.2.4.2.  Initial Content  . . . . . . . . . . . . . . . .  15
   12. Privacy Considerations  . . . . . . . . . . . . . . . . . . .  15
   13. Security Considerations . . . . . . . . . . . . . . . . . . .  16
   14. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  16
   15. References  . . . . . . . . . . . . . . . . . . . . . . . . .  16
     15.1.  Normative References . . . . . . . . . . . . . . . . . .  17
     15.2.  Informative References . . . . . . . . . . . . . . . . .  18
   Appendix A.  Paradigms to Enforce Access Control on Reverse Search
           in RDAP . . . . . . . . . . . . . . . . . . . . . . . . .  19
   Appendix B.  Change Log . . . . . . . . . . . . . . . . . . . . .  19
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  21

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1.  Introduction

   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, detecting cybercrimes), its
   availability as a standardized Whois 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-RDS1]
   [ICANN-RDS2] [ICANN-RA], which 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 [RFC3912] in the context of such directory
   services.  Since RDAP consequently permits a reverse search
   implementation complying with privacy protection principles, this
   objection is not well-founded.

   The other 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 distinction on which
   this objection is based 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;
   *  the need for such data to perform bulk 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.

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   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 in relationship with another matching a given search
   pattern.

   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.

1.1.  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 in the following:

   *  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;

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   *  search-condition: a sequence of "property=search pattern"
      predicates separated by the ampersand character ('&', US-ASCII
      value 0x0026).  Each "property" maps to a member of the RDAP
      object class corresponding to "related-resource-type".  Objects
      are only included in the search results if they satisfy all
      included predicates.  This includes predicates that are for the
      same property: it is necessary in such a case for the related
      object to match against each of those predicates.  Based on their
      policy, servers MAY restrict the usage of predicates to make a
      valid search condition, by returning a 400 (Bad Request) response
      when a problematic request is received.

   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.

   Partial string matching in search patterns is allowed as defined in
   section 4.1 of [RFC9082].

3.  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.

4.  Reverse Search Definition

   Based on the content of Section 2, defining a reverse search means to
   define the triple <searchable resorce 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
   [I-D.ietf-jsonpath-base].  Reverse searches are registered in the
   Reverse Search registry (see Section 11.2.3), while reverse search
   mappings are registered in the Reverse Search Mapping registry
   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 6).

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   All of the reverse searches defined by this document (see Section 7)
   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 6) will typically lead to a member with a different name
   being used for the search.

   Servers MUST NOT provide or implement unregistered reverse searches
   or unregistered reverse search mappings.

5.  Reverse Search Properties Discovery

   Servers complying with this specification MUST extend the help
   response [RFC9083] with the "reverse_search_properties" member which
   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.

6.  Reverse Search Properties Mapping

   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 remapping the reverse search property to some new
   member (in the case of restructuring).

   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.

   The "reverse_search_properties_mapping" member contains an array of
   objects with the following mandatory child members:

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   "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
      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.

   An example of a reverse search response including the
   "reverse_search_properties_mapping" member is shown in Figure 3.

7.  Reverse Searches Based on Entity Details

   Since in RDAP, an entity can be associated with any other object
   class, 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, and entity searchable resource
   types and the entity related resource type:

   Reverse search property:  role
   RDAP property path:  $..entities[*].roles
   Reference:  Section 10.2.4 of [RFC9083]

   Reverse search property:  handle
   RDAP property path:  $..entities[*].handle
   Reference:  Section 5.1 of [RFC9083]

   Reverse search property:  fn
   RDAP property path:  $..entities[*].vcardArray[1][?(@[0]=='fn')][3]
   Reference:  Section 6.2.1 of [RFC6350]

   Reverse search property:  email
   RDAP property path:  $..entities[*].vcardArray[1][?(@[0]=='email')][3

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      ]
   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

   An example of the help response including the reverse search
   properties supported is shown below.

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      {
        "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 a response including the mapping that is occurring for
   the first reverse search in Figure 1 is shown below.

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      {
        "rdapConformance": [
          "rdap_level_0",
          "reverse_search"
        ],
        ...
        "reverse_search_properties": [
          {
            "property": "handle",
            "propertyPath": "$..entities[*].handle"
          },
          {
            "property": "role",
            "propertyPath": "$..entities[*].roles"
          }
        ],
        ...
      }

                                  Figure 3

8.  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.

9.  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].

10.  Implementation Status

   NOTE: Please remove this section and the reference to RFC 7942 prior
   to publication as an RFC.

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   This section records the status of known implementations of the
   protocol defined by this specification at the time of posting of this
   Internet-Draft, and is based on a proposal described in [RFC7942].
   The description of implementations in this section is intended to
   assist the IETF in its decision processes in progressing drafts to
   RFCs.  Please note that the listing of any individual implementation
   here does not imply endorsement by the IETF.  Furthermore, no effort
   has been spent to verify the information presented here that was
   supplied by IETF contributors.  This is not intended as, and must not
   be construed to be, a catalog of available implementations or their
   features.  Readers are advised to note that other implementations may
   exist.

   According to RFC 7942, "this will allow reviewers and working groups
   to assign due consideration to documents that have the benefit of
   running code, which may serve as evidence of valuable experimentation
   and feedback that have made the implemented protocols more mature.
   It is up to the individual working groups to use this information as
   they see fit".

10.1.  IIT-CNR/Registro.it RDAP Server

   *  Responsible Organization: Institute of Informatics and Telematics
      of National Research Council (IIT-CNR)/Registro.it
   *  Location: https://rdap.pubtest.nic.it/
   *  Description: This implementation includes support for RDAP queries
      using data from the public test environment of .it ccTLD.  Reverse
      search is allowed to authenticated users.  Registrar users are
      allowed to perform reverse searches on their own domains and
      contacts.  This is achieved by adding an implicit predicate to the
      search condition.
   *  Level of Maturity: This is an "alpha" test implementation.
   *  Coverage: This implementation includes all of the features
      described in this specification.
   *  Contact Information: Mario Loffredo, mario.loffredo@iit.cnr.it

10.2.  IIT-CNR/Registro.it RDAP Client

   *  Responsible Organization: Institute of Informatics and Telematics
      of National Research Council (IIT-CNR)/Registro.it
   *  Location: https://web-rdap.pubtest.nic.it/
   *  Description: This is a Javascript web-based RDAP client.  RDAP
      responses are retrieved from RDAP servers by the browser, parsed
      into an HTML representation, and displayed in a format improving
      the user experience.  Reverse search is allowed to authenticated
      users.
   *  Level of Maturity: This is an "alpha" test implementation.

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   *  Coverage: This implementation includes all of the features
      described in this specification.
   *  Contact Information: Francesco Donini, francesco.donini@iit.cnr.it

11.  IANA Considerations

11.1.  RDAP Extensions Registry

   IANA is requested to register the following value in the "RDAP
   Extensions" registry:

   *  Extension identifier: reverse_search
   *  Registry operator: Any
   *  Published specification: This document.
   *  Contact: IETF <iesg@ietf.org>
   *  Intended usage: This extension identifier is used for reverse
      search URI path segments.

11.2.  RDAP Reverse Search Registries

11.2.1.  Creation of the RDAP Reverse Search Registries

   IANA is requested to create the "RDAP Reverse Search" and "RDAP
   Reverse Search Mapping" registries.

   These registries follow the Specification Required process as defined
   in Section 4.5 of [RFC8126].

   The designated expert should prevent collisions and confirm that
   suitable documentation, as described in Section 4.6 of [RFC8126], is
   available to ensure interoperability.  References are not limited
   only to RFCs and simple definitions could be described in the
   registries themselves.

   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.

11.2.2.  Submit Request to IANA

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

11.2.3.  RDAP Reverse Search Registry

11.2.3.1.  Template

   "Searchable Resource Type":  The searchable resource type of the

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      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.

   "Property":  The name of the reverse search property.

   "Description":  A brief human-readable text describing the reverse
      search property.

   "Registrant Name":  The name of the person registering the reverse
      search property.

   "Registrant 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 is requested to register the following entries in the "RDAP
   Reverse Search" registry:

   Searchable Resource Type:  domains, nameservers, entities
   Related Resource Type:  entity
   Property:  fn
   Description:  The server supports the domain/nameserver/entity search
      based on the full name (a.k.a formatted name) of an associated
      entity.
   Registrant Name:  IESG
   Registrant Contact Information:  iesg@ietf.org
   Reference:  This document, Section 7

   Searchable Resource Type:  domains, nameservers, entities
   Related Resource Type:  entity
   Property:  handle
   Description:  The server supports the domain/nameserver/entity search
      based on the handle of an associated entity.
   Registrant Name:  IESG
   Registrant Contact Information:  iesg@ietf.org
   Reference:  This document, Section 7

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   Searchable Resource Type:  domains, nameservers, entities
   Related Resource Type:  entity
   Property:  email
   Description:  The server supports the domain/nameserver/entity search
      based on the email address of an associated entity.
   Registrant Name:  IESG
   Registrant Contact Information:  iesg@ietf.org
   Reference:  This document, Section 7

   Searchable Resource Type:  domains, nameservers, entities
   Related Resource Type:  entity
   Property:  role
   Description:  The server supports the domain/nameserver/entity search
      based on the role of an associated entity.
   Registrant Name:  IESG
   Registrant Contact Information:  iesg@ietf.org
   Reference:  This document, Section 7

11.2.4.  RDAP Reverse Search Mapping Registry

11.2.4.1.  Template

   "Searchable Resource Type":  The same as defined in the "Reverse
      Search Registry".

   "Related Resource Type":  The same as defined in the "Reverse Search
      Registry".

   "Property":  The same as defined in the "Reverse Search Registry".

   "Property Path":  The JSONPath of the RDAP property this reverse
      search property maps to.

   "Registrant Name":  The name of the person registering this reverse
      search property mapping.

   "Registrant Contact Information":  The same as defined in the
      "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.

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11.2.4.2.  Initial Content

   IANA is requested to register the following entries in the "RDAP
   Reverse Search Mapping" registry:

   Searchable Resource Type:  domains, nameservers, entities
   Related Resource Type:  entity
   Property:  fn
   Property Path:  $..entities[*].vcardArray[1][?(@[0]=='fn')][3]
   Registrant Name:  IESG
   Registrant Contact Information:  iesg@ietf.org
   Reference:  This document, Section 7

   Searchable Resource Type:  domains, nameservers, entities
   Related Resource Type:  entity
   Property:  handle
   Property Path:  $..entities[*].handle
   Registrant Name:  IESG
   Registrant Contact Information:  iesg@ietf.org
   Reference:  This document, Section 7

   Searchable Resource Type:  domains, nameservers, entities
   Related Resource Type:  entity
   Property:  email
   Property Path:  $..entities[*].vcardArray[1][?(@[0]=='email')][3]
   Registrant Name:  IESG
   Registrant Contact Information:  iesg@ietf.org
   Reference:  This document, Section 7

   Searchable Resource Type:  domains, nameservers, entities
   Related Resource Type:  entity
   Property:  role
   Property Path:  $..entities[*].roles
   Registrant Name:  IESG
   Registrant Contact Information:  iesg@ietf.org
   Reference:  This document, Section 7

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 tradeoffs
   that result from implementation of this functionality.

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   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 general, given the sensitivity of this functionality, it SHOULD be
   accessible to authorized users only, and for specific use cases only.

   Since reverse search requests and responses could contain Personally
   Identifiable Information (PII), reverse search functionality SHOULD
   be available over HTTPS only.

   Providing reverse search in RDAP carries the following threats as
   described in [RFC6973]:

   *  Correlation
   *  Disclosure
   *  Misuse of information

   Therefore, RDAP providers are REQUIRED to mitigate the risk of those
   threats by implementing appropriate measures supported by security
   services (see Section 13).

13.  Security Considerations

   Security services 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.

   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.  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.

15.  References

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15.1.  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>.

   [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>.

   [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>.

   [RFC7480]  Newton, A., Ellacott, B., and N. Kong, "HTTP Usage in the
              Registration Data Access Protocol (RDAP)", STD 95,
              RFC 7480, DOI 10.17487/RFC7480, March 2015,
              <https://www.rfc-editor.org/info/rfc7480>.

   [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>.

   [RFC7942]  Sheffer, Y. and A. Farrel, "Improving Awareness of Running
              Code: The Implementation Status Section", BCP 205,
              RFC 7942, DOI 10.17487/RFC7942, July 2016,
              <https://www.rfc-editor.org/info/rfc7942>.

   [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>.

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   [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>.

15.2.  Informative References

   [I-D.ietf-jsonpath-base]
              Gössner, S., Normington, G., and C. Bormann, "JSONPath:
              Query expressions for JSON", Work in Progress, Internet-
              Draft, draft-ietf-jsonpath-base-10, 6 February 2023,
              <https://datatracker.ietf.org/doc/html/draft-ietf-
              jsonpath-base-10>.

   [ICANN-RA] Internet Corporation For Assigned Names and Numbers,
              "Registry Agreement", July 2017,
              <https://newgtlds.icann.org/sites/default/files/
              agreements/agreement-approved-31jul17-en.pdf>.

   [ICANN-RDS1]
              Internet Corporation For Assigned Names and Numbers,
              "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>.

   [ICANN-RDS2]
              Internet Corporation For Assigned Names and Numbers,
              "Final Issue Report on a Next-Generation gTLD RDS to
              Replace WHOIS", October 2015,
              <http://whois.icann.org/sites/default/files/files/final-
              issue-report-next-generation-rds-07oct15-en.pdf>.

   [OIDCC]    OpenID Foundation, "OpenID Connect Core incorporating
              errata set 1", November 2014,
              <http://openid.net/specs/openid-connect-core-1_0.html>.

   [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>.

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   [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 reported
   here in the following leverage the capabilities either supported
   natively or provided as extensions by the OpenID Connect [OIDCC]:

   *  Role-Based Access Control: 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: 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: 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 by setting within an out-of-band process additional
      OpenID Connect claims describing the request context and making
      the RDAP server check the compliance between the given context and
      the control rules applied to the data to be returned;
   *  Time-Based Access Control: data access is allowed for a limited
      time only.  It can be implemented by assigning the users with
      temporary credentials linked to access grants whose scope is
      limited.

Appendix B.  Change Log

   00:  Initial working group version ported from draft-loffredo-regext-
      rdap-reverse-search-04
   01:  Updated "Privacy Considerations" section.
   02:  Revised the text.
   03:  Refactored the query model.

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   04:  Keepalive refresh.
   05:  Reorganized "Abstract".  Corrected "Conventions Used in This
      Document" section.  Added "RDAP Conformance" section.  Changed
      "IANA Considerations" section.  Added references to RFC7095 and
      RFC8174.  Other minor edits.
   06:  Updated "Privacy Considerations", "Security Considerations" and
      "Acknowledgements" sections.  Added some normative and informative
      references.  Added Appendix A.
   07:  Updated normative references.
   08:  Changed "Implementation Status" section.  Updated informative
      references.
   09:  Extended the query model to represent a reverse search based on
      any relationship between the RDAP object classes.  Changed the
      path segment "role" into a query parameter.
   10:  Updated "Reverse Searches Based on Entity Details" section to
      consider the use of JSContact format instead of jCard.  Added
      references to JSContact documents.
   11:  Updated the document based on Tom Harrison and James Gould
      feedback:
      *  Updated section "RDAP Path Segment Specification":
         -  Clarified how servers must evaluate a reverse search
            including predicates that are for the same property.
         -  Specified the error response servers must return when
            receiving a wrong reverse search request according to their
            policy.
         -  Clarified that searchs for the related-resource-type values
            other than "entity" may be defined in future documents.
      *  Reviewed text in section "Reverse Searches Based on Entity
         Details" about reverse searches based on custom response
         extensions.
      *  Removed references to JSContact documents in section "Reverse
         Searches Based on Entity Details".  Moved the mapping between
         jCard properties used in the RDAP response and JSContact
         counterparts to draft-ietf-regext-rdap-jscontact.
      *  Added section "RDAP Response Specification".
      *  Changed the text to present reverse search as a single
         extension with multiple features.
      *  Changed the definition of searchable-resource-type and related-
         resource-type to consider also the resource type extensions.
      *  Replaced "reverse" with "reverse_search_0" in the generic
         reverse search path.  Updated Figure 1 accordingly.
      *  Removed the phrase "but with a special focus on its privacy
         implications" from both the "Abstract" and the "Introduction".
         Moved the mapping between jCard properties used in the RDAP
         response and JSContact counterparts to draft-ietf-regext-rdap-
         jscontact.
      *  Reviewed the text of "Privacy Considerations" section.
      *  Text cleaning.

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   12:  Replaced "reverse_search_0" with "reverse_search" as both URI
      path segment, extension identifier and rdapConformance tag to
      match the working group consensus.
   13:  Done some minor text changes.
   14:  Revised text of first sentence and added references to RFC8977
      and RFC8982 in the "Implementation Considerations" section.
   15:  Moved RFC6973 from Normative References to Informative
      References.  Remnoved informative reference to draft-ietf-regext-
      rdap-openid.  Rephrased text in Appendix A accordingly.
   16:  Moved OIDC from Normative References to Informative References.
      Added the "Reverse Search Properties Discovery" section.  Added
      "RDAP JSON Values Registry" as a subsection of the "IANA
      Considerations" section.  Rephrased the "Reverse Searches Based on
      Entity Details" section to refer to the "Reverse Search Properties
      Discovery" section.  Updated the "Acknowledgements" section.
      Minor text edits.
   17:  Revised the "Reverse Search Properties Discovery" section.
      Replaced "RDAP JSON Values Registry" section with the "RDAP
      Reverse Search Properties Registry" section.
   18:  Changed "Expert Review" with "Specification Required" in the
      "Creation of the RDAP Reverse Search Properties Registry" section.
      Renamed the "RDAP Reverse Search Properties Registry" into "RDAP
      Reverse Search Registry".  Aligned the RDAP Reverse Search
      Registry template with the initial content.  Introduced the
      "reverse_search_properties_mapping" response extension.  Added the
      "RDAP Reverse Search Mapping Registry".  Reorganized the document
      to separate the implementation of a generic reverse search from
      that based on domain-entity relationship.

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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