Registration Protocols Extensions                            M. Loffredo
Internet-Draft                                             M. Martinelli
Intended status: Standards Track                     IIT-CNR/
Expires: 14 August 2022 10 February October 2022                                    8 April 2022

  Registration Data Access Protocol (RDAP) Reverse search capabilities


   The Registration Data Access Protocol (RDAP) does not include query
   capabilities to find 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
   scenario.  This document describes RDAP query extensions 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
   relationship is treated as a particular case but with a special focus
   on its privacy implications.

Status of This Memo

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Table of Contents

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

1.  Introduction

   Reverse Whois is a service provided by many web applications that
   allow 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 the potential risks of privacy
   violation.  However, TLDs 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 policies to enforce
   the requestor accreditation, authentication, authorization, and terms
   and conditions of data use.  It is well known that such security
   policies are not implemented in Whois [RFC3912], while they are in
   RDAP [RFC7481].  Therefore, RDAP permits a reverse search
   implementation complying with privacy protection principles.

   The other objection to the implementation of a reverse search
   capability has been connected with its impact on server processing.
   Since RDAP supports search queries, the impact of both standard and
   reverse searches is equivalent and can be mitigated by servers
   adopting ad hoc strategies.  Furthermore, the reverse search is
   almost always performed by specifying an entity role (e.g.
   registrant, technical contact) and this can contribute to restricting
   the result set.

   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 massive 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
   any 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].

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
   [RFC9082].  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 resource types for
      search defined in Section 3.2 of [RFC9082], i.e. "domains",
      "nameservers" and "entities";
   *  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";
   *  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 are joined by the AND logical operator.  Based
      on their policy, servers MAY restrict the usage of predicates to
      make a valid search condition.

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

2.1.  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 based on the
   entity 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 regardless of the searchable resource type being selected:

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

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

   Reverse search property:  fn
   Using jCard:
   RDAP property:  $..entities[*].vcardArray[1][?(@[0]=='fn')][3]
   RFC reference:
   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]
   RFC reference:
   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 definitions above, 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]. [I-D.ietf-jsonpath-base];
   *  The  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. role;
   *  Some of  the last two properties are related to jCard elements [RFC7095]
      but, being jCard the JSON format for vCard [RFC6350], vCard, the corresponding RFC
      reference is to the vCard specification [RFC6350].  Such
      properties are also shown according to the JSContact format
      [I-D.ietf-calext-jscontact] to address the case when it is used
      instead of jCard as described in [I-D.ietf-regext-rdap-jscontact].

   Servers MAY implement other properties than those defined in this

   Examples of reverse search paths based on the domain-entity
   relationship are presented below:




                                  Figure 1

3.  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 6.

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 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.  In addition, the risks to degrade the performance
   or to generate huge result sets can be mitigated by adopting the same
   policies valid for handling searches (e.g. restricting the search
   functionality, limiting the rate of search requests according to the
   user profile, truncating and paging the results, returning partial

5.  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".

5.1.  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 to the
      search pattern.
   *  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,

5.2.  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,

6.  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.

7.  Privacy Considerations

   The use of the capability described in this document whenever a
   contact detail is taken MUST be compliant with the rules about
   privacy protection each RDAP provider is subject to.  Sensitive
   registration data MUST be protected and accessible for permissible
   purposes only.  This feature SHOULD be only accessible to authorized
   users and only for a specified use case.

   Since the request for this feature could contain Personal
   Identifiable Information, it SHOULD only be accessible to authorized
   users and available over HTTPS.

   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.  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.

9.  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
   Ulrich Wisser.

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

10.  References

10.1.  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,

10.2.  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.  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 the intended usage 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 data to be returned.  The
      purpose can be stated within an out-of-band process by setting the
      OpenID Connect 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 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.

Authors' Addresses
   Mario Loffredo
   Via Moruzzi,1
   56124 Pisa

   Maurizio Martinelli
   Via Moruzzi,1
   56124 Pisa