Registration Protocols Extensions                            M. Loffredo
Internet-Draft                                             M. Martinelli
Intended status: Standards Track                     IIT-CNR/
Expires: October 11, 2021                                  April 9, 2021

  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 to any defined object class.  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 between any searchable object and the related entities.

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
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on October 11, 2021.

Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   ( in effect on the date of
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

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

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 cybercrime cases), its
   availability as a standardized Whois capability has been objected 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.

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   Another 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:

   o  the loss of synchronization between the registrar database and the
      registry database;

   o  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 way for a client to search for
   the collection of domains associated with an entity [RFC7482].  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
   [RFC7483], the availability of a reverse search can be common to all
   resource type path segments defined for search.

   The protocol described in this specification aims to extend the RDAP
   query capabilities to enable the reverse search based on the
   relationship between any object and the associated entities.  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.

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2.  RDAP Path Segment Specification

   The new search paths are OPTIONAL extensions of those defined in
   [RFC7482].  A generic reverse search path is described by the syntax:

   {resource-type}/reverse/{role}?{property}=<search pattern>

   The path segments are defined as in the following:

   o  resource-type: it MUST be one of resource type path segments
      defined in Section 3.2 of [RFC7482]: "domains", "nameservers" or

   o  role: it MUST be one of the roles described in Section 10.2.4 of
      [RFC7483].  For role independent reverse searches, the value
      "entity" MUST be used;

   o  property: it identifies the entity property to be used in matching
      the search pattern.  A pre-defined list of properties includes:
      fn, handle, email, city, country, cc.  The mapping between such
      properties and the RDAP properties is shown in Table 1.  Some of
      the properties are related to jCard elements [RFC7095] but, being
      jCard the JSON format for vCard [RFC6350], the corresponding
      definitions are included in vCard specification.  Servers MAY
      implement additional properties to those defined in this document.

   Partial string matching is allowed as defined in section 4.1 of

   | Reverse search    | RDAP property      | RFC    | RFC    | RFC    |
   | property          |                    | 7483   | 6350   | 8605   |
   | handle            | handle             | 5.1.   |        |        |
   | fn                | jCard fn           |        | 6.2.1  |        |
   | email             | jCard email        |        | 6.4.2  |        |
   | city              | locality in jCard  |        | 6.3.1  |        |
   |                   | adr                |        |        |        |
   | country           | country name in    |        | 6.3.1  |        |
   |                   | jCard adr          |        |        |        |
   | cc                | country code in    |        |        | 3.1    |
   |                   | jCard adr          |        |        |        |

    Table 1: Mapping between the reverse search properties and the RDAP

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               Figure 1: Examples of reverse search queries

   The "country" property can be used as an alternative to "cc" when
   RDAP servers don't include the jCard "cc" parameter [RFC8605] in
   their response.

3.  RDAP Conformance

   Servers complying with this specification MUST include the value
   "reverse_search" in the rdapConformance property of the help response
   [RFC7483].  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.
   Both handle and fn are used as standard path segments to search for
   entities [RFC7482].  With regards to the other reverse search
   properties, namely email, city and country code, the impact of their
   usage on server processing is evaluated to be the same as other
   existing query capabilities (e.g. wildcard prefixed search pattern)
   so the risks to degrade the performance or to generate huge result
   sets can be mitigated by adopting the same policies (e.g. restricting
   the search functionality, limiting the rate of search requests
   according to the user profile, truncating and paging the results,
   returning partial responses).

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

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   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/

      Responsible Organization: Institute of Informatics and Telematics
      of National Research Council (IIT-CNR)/
      Description: This implementation includes support for RDAP queries
      using data from the public test environment of .it ccTLD.
      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,

6.  IANA Considerations

   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 <>
      Intended usage: This extension describes reverse search query
      patterns for RDAP.

7.  Privacy Considerations

   The use of the capability described in this document 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 functionality SHOULD
   be only accessible to authorized users and only for a specified use

   Already the request for this functionality could contain Personal
   Identifiable Information and SHOULD therefore only be available over

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

   o  Correlation
   o  Disclosure
   o  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 entity role within the reverse search path
   allows the RDAP servers to implement different authorization policies
   on a per-role basis.

9.  Acknowledgements

   The authors would like to acknowledge the following individuals for
   their contributions to this document: Tom Harrison, Scott Hollenbeck,
   Francisco Arias, Gustavo Lozano, Eduardo Alvarez and Ulrich Wisser.

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,

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   [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,

   [RFC7482]  Newton, A. and S. Hollenbeck, "Registration Data Access
              Protocol (RDAP) Query Format", RFC 7482,
              DOI 10.17487/RFC7482, March 2015,

   [RFC7483]  Newton, A. and S. Hollenbeck, "JSON Responses for the
              Registration Data Access Protocol (RDAP)", RFC 7483,
              DOI 10.17487/RFC7483, 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, <>.

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   [RFC8605]  Hollenbeck, S. and R. Carney, "vCard Format Extensions:
              ICANN Extensions for the Registration Data Access Protocol
              (RDAP)", RFC 8605, DOI 10.17487/RFC8605, May 2019,

10.2.  Informative References

              Hollenbeck, S., "Federated Authentication for the
              Registration Data Access Protocol (RDAP) using OpenID
              Connect", <

              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]:

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   o  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;

   o  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

   o  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;

   o  Time-Based Access Control: data access is allowed for 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-
   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.

Authors' Addresses

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   Mario Loffredo
   Via Moruzzi,1
   Pisa  56124


   Maurizio Martinelli
   Via Moruzzi,1
   Pisa  56124


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