Registration Protocols Extensions                            M. Loffredo
Internet-Draft                                             M. Martinelli
Intended status: Standards Track                     IIT-CNR/
Expires: 10 October 3 November 2022                                    8 April                                      2 May 2022

  Registration Data Access Protocol (RDAP) Reverse search capabilities


   The Registration Data Access Protocol (RDAP) does not include query
   capabilities to find for finding the list of domains related to a set of
   entities matching a given search pattern.  In the RDAP context, an
   entity can be associated with any defined object class.  Moreover,
   other relationships between object classes exist and might be used
   for providing a reverse search capability.  Therefore, a reverse
   search can be applied to other use cases than the classic domain-entity domain-
   entity scenario.  This document describes an RDAP query extensions extension that
   allow 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 domain-
   entity relationship is treated as a particular case but with a special focus
   on its privacy implications. case.

Status of This Memo

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   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on 10 October 3 November 2022.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Conventions Used in This Document . . . . . . . . . . . .   4
   2.  RDAP Path Segment Specification . . . . . . . . . . . . . . .   4
   3.  RDAP Response Specification . . . . . . . . . . . . . . . . .   5
   4.  Reverse Searches Based on Entity Details  . . . . . . . .   4
   3. . .   5
   5.  RDAP Conformance  . . . . . . . . . . . . . . . . . . . . . .   6
   6.  Implementation Considerations . . . . . . . . . . . . . . . .   6
   7.  Implementation Status . . . . . . . . . . . . . . . . . . . .   6
     5.1.   7
     7.1.  IIT-CNR/ RDAP Server . . . . . . . . . . . . .   7
     7.2.  IIT-CNR/ RDAP Client . . . . . . . . . . . . .   7
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   7.   8
   9.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .   8
   10. Security Considerations . . . . . . . . . . . . . . . . . . .   8
   9.   9
   11. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   8
   10.   9
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     12.1.  Normative References . . . . . . . . . . . . . . . . . .   9
     12.2.  Informative References . . . . . . . . . . . . . . . . .  10
   Appendix A.  Paradigms to Enforce Access Control on Reverse Search
           in RDAP . . . . . . . . . . . . . . . . . . . . . . . . .  11
   Appendix B.  Change Log . . . . . . . . . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12  13

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

   The first objection has been caused by concerns the potential risks of privacy
   violation.  However, TLDs 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 according to adequate in accordance with appropriate policies to enforce
   for requestor accreditation, authentication, authorization, and terms authentication and conditions of data use.  It is well known authorization.
   RDAP's reliance on HTTP means that such security
   policies are not implemented in it can make use of common HTTP-
   based approaches to authentication and authorization, making it more
   useful than Whois [RFC3912], while they are [RFC3912] in the context of such directory
   services.  Since RDAP [RFC7481].  Therefore, RDAP consequently permits a reverse search
   implementation complying with privacy protection principles. 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 supports specifications already define search queries,
   with similar processing requirements, so the impact of both standard and
   reverse searches distinction on which
   this objection is equivalent and can be mitigated by servers
   adopting ad hoc strategies.  Furthermore, the reverse search based is
   almost always performed by specifying an entity role (e.g.
   registrant, technical contact) and this can contribute to restricting
   the result set. not clear.

   Reverse searches, such as finding the list of domain names associated
   with contacts or nameservers 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 massive 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.
   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

   The protocol described in this specification aims to extend the RDAP
   query capabilities to enable the 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
   query model but with a special focus on its privacy implications.
   The extension is implemented by adding new path segments (i.e. search
   paths) and using a RESTful web service [REST].  The service is
   implemented using the Hypertext Transfer Protocol (HTTP) [RFC7230]
   and the conventions described in [RFC7480]. model.

1.1.  Conventions Used in This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "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.  RDAP Path Segment Specification

   The new search paths are OPTIONAL extensions of those defined in

   A generic reverse search path is described by the syntax:



   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. [RFC9082] (i.e. "domains",
      "nameservers" and "entities"; "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. [RFC9082] (i.e. "domain",
      "nameserver", "entity", "ip" and "autnum"; "autnum") or a resource type
   *  search-condition: a sequence of "property=search pattern"
      predicates separated by the ampersand character ('&', US-ASCII
      value 0x0026).  Each "property" represents a JSON object property
      of the RDAP object class corresponding to "related-resource-type".
      All the predicates
      Objects are joined by only included in the AND logical operator.  Based
      on 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. 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 searches defined in this document are for
   a related-resource-type of "entity".  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.  RDAP 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 Searches Based on Entity Details

   Since in RDAP, an entity can be associated with any other object
   class, the most common kind of reverse searches are search is one based on the
   entity an
   entity's details.  Such reverse searches arise from the above 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

   This section defines the following reverse search properties to be
   used servers
   SHOULD support regardless of the searchable resource type being

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

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

   Reverse search property:  fn
   Using jCard:
   RDAP property:  $..entities[*].vcardArray[1][?(@[0]=='fn')][3]
   Reference:  Section 6.2.1 of [RFC6350]
   Using JSContact:
   RDAP property:  $..entities[*].jscard.fullName
   Reference:  Section 2.2.2 of [I-D.ietf-calext-jscontact]

   Reverse search property:  email
   Using jCard:
   RDAP property:  $..entities[*].vcardArray[1][?(@[0]=='email')][3]
   Reference:  Section 6.4.2 of [RFC6350]
   Using JSContact:
   RDAP property:  $..entities[*].jscard.emails.[*].email
   Reference:  Section 2.3.1 of [I-D.ietf-calext-jscontact]

   Regarding the above definitions, it must be noted that:

   *  the

   The mapping between the reverse search property and the corresponding
   RDAP response property is done through the use of a JSONPath
   expression [I-D.ietf-jsonpath-base];
   *  the [I-D.ietf-jsonpath-base].

   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 role.

   The last two properties are related to jCard elements [RFC7095]
      but, being [RFC7095], but
   the field references are to vCard [RFC6350], since jCard is the JSON
   format for vCard, vCard.

   Examples of reverse search paths based on the corresponding
      reference is to domain-entity
   relationship are presented in Figure 1.




                                Figure 1

   Documents that deprecate or restructure RDAP responses such that one
   or more of the vCard specification [RFC6350].  Such properties are also shown according to listed above becomes invalid MUST either
   note that the JSContact format
      [I-D.ietf-calext-jscontact] relevant reverse search is no longer available (in the
   case of deprecation) or describe how to address continue supporting the
   relevant search by way of some new RDAP property (in the case when it is used
      instead of jCard as described

   A server that includes additional fields in [I-D.ietf-regext-rdap-jscontact].

   Servers its objects in accordance
   with the extensibility provisions of section 6 of [RFC7480] MAY implement other properties than
   support the use of those fields in search conditions, in the same way
   as for the search conditions defined in this section.

   Examples of  Support for
   such fields in the reverse search paths based on context MUST be documented in the domain-entity
   relationship are presented below:




                                  Figure 1

   extension specification.

5.  RDAP Conformance

   Servers complying with this specification MUST include the value
   "reverse_search_0" in the rdapConformance property of the help
   response [RFC9083].  The information needed to register this value in
   the "RDAP Extensions" registry is described in Section 8.


4.  Implementation Considerations

   The implementation of the proposed extension is technically feasible.

   To limit the impact of processing the search predicates, servers are
   RECOMMENDED to mandate the make use of at least one property among those
   mapped to indexed fields of the registry database.  Other properties,
   such as "role", MAY be allowed to further restrict the set of
   possible results. indexes and similar functionality in their
   underlying data store.  In addition, the risks with respect to degrade the
   performance degradation or to generate huge result sets set generation can be mitigated by
   adopting the same
   policies valid practices used for handling searches (e.g. standard searches, e.g. restricting the
   search functionality, limiting the rate of search requests according
   to the
   user profile, user's authorization, truncating and paging the results, and
   returning partial

5. responses.

7.  Implementation Status

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

   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

   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".


7.1.  IIT-CNR/ RDAP Server

   *  Responsible Organization: Institute of Informatics and Telematics
      of National Research Council (IIT-CNR)/
   *  Location:
   *  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 condition predicate to the
      search pattern. 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,


7.2.  IIT-CNR/ RDAP Client

   *  Responsible Organization: Institute of Informatics and Telematics
      of National Research Council (IIT-CNR)/
   *  Location:
   *  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
   *  Level of Maturity: This is an "alpha" test implementation.
   *  Coverage: This implementation includes all of the features
      described in this specification.
   *  Contact Information: Francesco Donini,


8.  IANA Considerations

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

   *  Extension identifier: reverse_search_0
   *  Registry operator: Any
   *  Published specification: This document.
   *  Contact: IETF <>
   *  Intended usage: This extension describes reverse search query
      patterns for RDAP.


9.  Privacy Considerations

   The use of the capability described search functionality defined in this document whenever a
   contact detail is taken MUST be compliant with may affect the rules about
   privacy protection each RDAP provider is subject to.  Sensitive
   registration data MUST be protected and accessible of entities in the registry (and elsewhere) in various ways:
   see [RFC6973] for permissible
   purposes only.  This feature a general treatment of privacy in protocol
   specifications.  Registry operators should be aware of the tradeoffs
   that result from implementation of 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 general, given the sensitivity of this functionality,it SHOULD be only
   accessible to authorized users only, and only for a specified specific use case. cases only.

   Since the request for this feature reverse search requests and responses could contain Personal Personally
   Identifiable Information, it Information (PII), reverse search functionality SHOULD only
   be accessible to authorized
   users and available over HTTPS. 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 8).

8. 10).

10.  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.


11.  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 and Alvarez, Ulrich Wisser.
   Wisser and James Gould.

   Tom Harrison and Jasdip Singh provided relevant feedback and constant
   support to the implementation of this proposal.  Their contributions
   have been greatly appreciated.


12.  References


12.1.  Normative References

   [OIDCC]    OpenID Foundation, "OpenID Connect Core incorporating
              errata set 1", November 2014,

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC3912]  Daigle, L., "WHOIS Protocol Specification", RFC 3912,
              DOI 10.17487/RFC3912, September 2004,

   [RFC5730]  Hollenbeck, S., "Extensible Provisioning Protocol (EPP)",
              STD 69, RFC 5730, DOI 10.17487/RFC5730, August 2009,

   [RFC6350]  Perreault, S., "vCard Format Specification", RFC 6350,
              DOI 10.17487/RFC6350, August 2011,

   [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,

   [RFC7095]  Kewisch, P., "jCard: The JSON Format for vCard", RFC 7095,
              DOI 10.17487/RFC7095, January 2014,

   [RFC7230]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Message Syntax and Routing",
              RFC 7230, DOI 10.17487/RFC7230, June 2014,

   [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,

   [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,

   [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,

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <>.

   [RFC9082]  Hollenbeck, S. and A. Newton, "Registration Data Access
              Protocol (RDAP) Query Format", STD 95, RFC 9082,
              DOI 10.17487/RFC9082, June 2021,

   [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,


12.2.  Informative References

              Stepanek, R. and M. Loffredo, "JSContact: A JSON
              representation of contact data", Work in Progress,
              Internet-Draft, draft-ietf-calext-jscontact-00, 17 January
              2020, <

              Gössner, S., Normington, G., and C. Bormann, "JSONPath:
              Query expressions for JSON", Work in Progress, Internet-
              Draft, draft-ietf-jsonpath-base-03, 16 January 2022,

              Loffredo, M. and G. Brown, "Using JSContact in
              Registration Data Access Protocol (RDAP) JSON Responses",
              Work in Progress, Internet-Draft, draft-ietf-regext-rdap-
              jscontact-09, 7 March 2022,

              Hollenbeck, S., "Federated Authentication for the
              Registration Data Access Protocol (RDAP) using OpenID
              Connect", Work in Progress, Internet-Draft, draft-ietf-
              regext-rdap-openid-08, 8 November 2021,

   [ICANN-RA] Internet Corporation For Assigned Names and Numbers,
              "Registry Agreement", July 2017,

              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,

              Internet Corporation For Assigned Names and Numbers,
              "Final Issue Report on a Next-Generation gTLD RDS to
              Replace WHOIS", October 2015,

   [REST]     Fielding, R., "Architectural Styles and the Design of
              Network-based Software Architectures", 2000,

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

   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 each category with static grants. 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 which means purpose, being the intended usage 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.
      The purpose can be stated within an out-of-band process by setting
      the OpenID Connect RDAP specific RDAP-specific "purpose" claim as defined in
   *  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

Appendix B.  Change Log

   00:  Initial working group version ported from draft-loffredo-regext-
   01:  Updated "Privacy Considerations" section.
   02:  Revised the text.
   03:  Refactored the query model.
   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
   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
      *  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
         -  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
      *  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-
      *  Reviewed the text of "Privacy Considerations" section.
      *  Text cleaning.

Authors' Addresses

   Mario Loffredo
   Via Moruzzi,1
   56124 Pisa

   Maurizio Martinelli
   Via Moruzzi,1
   56124 Pisa